Nudibranchs of the Central Western

Australian Coast

Justine M. Arnold

This thesis is presented as part of the requirements for the Degree of Bachelor of Science

in Marine Science with Honours at Murdoch University.

October 2014

i

DECLARATION

I declare that the work presented here is my own research conducted from March to

October 2014, and has not been submitted for the award of any other degree at another

tertiary institution.

Justine Arnold

October 2014

ii

ABSTRACT

Nudibranchs are a diverse group of gastropod molluscs that are distributed around the

world found inhabiting coral reef ecosystems. Baseline data on nudibranchs is lacking in

the mid west region of Western Australia. Four sub-regions across the Midwest;

Geraldton and the three groups at the Abrolhos Islands, the Easter Group, the Wallabi

Group and the Pelsaert Group were the focus of nudibranch diversity surveys. Collection

of quantitative information to establish a biogeographical baseline for the nudibranchs of

this region was one of the main aims of this study.

In total 89 dives were made over the duration of this study, with an average dive time of

30 minutes. A total of 296 individual nudibranchs were observed. The most abundant

family found was Chromodorididae and Chromodoris westraliensis was the dominant

species. Equal numbers of nudibranchs were found at shallow and deep sites, with depth

found to not have a significant difference on nudibranch abundance or species

abundance. Sub-region was suggested to be the predominant influence in nudibranch

abundance and species richness. The probable cause for this is the influence from the

Leeuwin Current and its effects on the habitat composition. The Leeuwin Current is

believed to strongly influence recruitment of planktonic larvae along the Western

Australian coast. Suggesting that larval recruitment of all marine species including

nudibranchs, nudibranch prey items and benthic flora nudibranchs inhabit is influenced by

the Leeuwin Current.

Investigations into key nudibranch prey items and their seasonal occurrence may help in

predicting abundance of sub-annual nudibranch species in an area. Benthic habitat

differences and nudibranch prey items could be distributed at different rate over each sub-

region due to local hydrology effects from the Leeuwin Current. Geraldton was found to

be clearly different to the three Abrolhos Island groups, with sub-region being a

determining factor for abundance and species abundance. Greater sampling effort into

iii

destructive day-time and night-time sampling is also predicted to increase the number of

species and abundance of nudibranchs found in the Midwest region.

iv

ACKNOWLEDGEMENTS

There are several people that deserve honorable mention for their assistance throughout

the duration of this study.

I was lucky enough to be the recipient of the Calver Family Scholarship for 2014. Thank

you for allowing me to be the recipient of such a highly regarded award. With the

assistance of the scholarship I was able to expand my research to areas that at first

seemed impossible.

I would like to thank my parents, Charlie and Lorraine Arnold, without their love, support

and encouragement I would not have been able to make it through the past 5 years at

university, especially this last year where they have bent over backwards and became

fully involved in my honours research. It was such an honor to spend so much time with

such giving people. Thank you.

I would like to extend my gratitude to my volunteer dive buddies for donating their

precious time to my research, Peter Howie, Rowan Kleindienst, Claire Cocking, Brenda

Arnold and Ellen Boylen, Thank you.

Thank you to Laura Bradshaw for always knowing the right thing to say and for last

minute technical assistance.

And to my supervisor Mike Van Keulen, Thank you; for taking me on-board, your endless

wealth of knowledge and advice and for allowing me the opportunity to apply the

numerous skills I have learnt in my undergraduate degree in this project.

v

TABLE OF CONTENTS

DECLARATION ...................................................................................................... i

ABSTRACT ............................................................................................................ ii

ACKNOWLEDGEMENTS ..................................................................................... iv

TABLE OF CONTENTS ......................................................................................... v

1.0 INTRODUCTION .......................................................................................... 1

1.1 Nudibranchs .................................................................................................. 2

1.1.1 Family Characteristics ............................................................................ 2

1.1.2 Distribution ............................................................................................. 2

1.1.3 Habitat and Feeding ............................................................................... 3

1.1.4 Life History ............................................................................................. 4

1.1.5 The Leeuwin Current .............................................................................. 5

1.2 Climate Change ............................................................................................ 7

1.2.1 Known Climate Change Impacts ............................................................ 8

1.2.2 Postulated Climate Change Impacts ...................................................... 9

1.3 Worldwide Nudibranch Diversity ................................................................... 9

1.4 Western Australian Nudibranch Diversity .................................................... 11

1.5 Aims of This Study ...................................................................................... 12

2.0 METHODS.................................................................................................. 14

2.1 Area Description ......................................................................................... 14

2.2 Environmental Description .......................................................................... 16

2.2.1 Wind ..................................................................................................... 16

2.2.2 Swell ..................................................................................................... 16

2.2.3 Current ................................................................................................. 17

2.2.4 Water Temperatures ............................................................................ 17

2.2.5 Salinity .................................................................................................. 18

2.3 Habitat Description ..................................................................................... 18

2.4 Site Selection .............................................................................................. 18

2.5 Survey Methods .......................................................................................... 19

2.6 Species Identification .................................................................................. 20

2.7 Statistical Analysis ...................................................................................... 21

2.7.1 Species and Abundance ...................................................................... 21

vi

2.7.2 Species Diversity and Evenness .......................................................... 22

2.7.3 Connectivity .......................................................................................... 23

3.0 RESULTS ................................................................................................... 24

3.1 Species and Abundance ............................................................................. 24

3.2 Family Level Analyses ................................................................................ 27

3.3 Total Abundance Analyses ......................................................................... 29

3.4 Total Species Analyses ............................................................................... 30

3.5 Interactions ................................................................................................. 32

3.6 Species Diversity and Evenness Indices .................................................... 33

3.7 Connectivity ................................................................................................ 35

3.8 Substrate Preference and Activity ............................................................... 38

4.0 DISCUSSION ............................................................................................. 40

4.1 Estimating and Comparing Diversity ........................................................... 40

4.2 Family Level Analysis ................................................................................. 42

4.3 Total Species and Abundance .................................................................... 44

4.4 Species Diversity and Evenness ................................................................. 47

4.5 Distribution .................................................................................................. 49

4.6 Substrate Preference and Activity ............................................................... 50

4.7 General Discussion ..................................................................................... 50

5.0 CONCLUSION ........................................................................................... 52

5.1. Future Implications .................................................................................... 53

6.0 REFERENCE LIST ..................................................................................... 54

7.0 APPENDIX ................................................................................................. 65

Appendice 1: ..................................................................................................... 65

Appendice 2: ..................................................................................................... 67

1

1.0 INTRODUCTION

Members of the sub-class Opisthobranchia are defined as mollusc gastropods that have,

over the course of evolution reduced their external shells, or have no shell (Martin et al.

2006). There are seven orders in the Opisthobranchia, one of these being Nudibranchia.

Individuals from Nudibranchia are defined as shell-less marine gastropods, commonly

referred to as sea-slugs (Hoover et al., 2012; Cheney et al., 2014). They have been

recorded in a wide range of habitats, from intertidal reef platforms in the tropics to

temperate areas in the deep sea (Chavanich et al., 2013). Due to nudibranchs being

cryptic, highly camouflaged, and therefore relatively hard to find, it has been difficult to

assess their diversity, species richness and abundance (Domenech et al. 2002;

Chavanich et al. 2013).

The local hydrology of a region and its impacts on nudibranch larval distribution are not

well known. Like all benthic marine invertebrates, nudibranchs have a planktonic larval

stage in their life cycle (Pechenik 1999; Todd et al. 1998). Attempts have been made to

identify trace elements in larvae carbonate structures, once they have settled, in an effort

to assess where larvae originated (Levin, 2006). This technique requires larvae to retain

the larval structure when settling out of the plankton, with gastropods required to retain

statoliths and prodissoconch (larval shell) (Levin, 2006). The majority of nudibranchs, lose

their shell on settling out of the plankton so it is near impossible to use this method (Levin,

2006).

Nudibranchs can be separated into three groups based on life cycles; sub-annual, annual

and biannual. Sub-annual nudibranchs are ephemeral species that undergo several

generations in one year (Todd, 1981). Annual species are nudibranchs that undergo a

single generation in one year; and biannual species have a post-larvae life of up to two

years in which they spawn once and then die (Todd, 1981). The distribution of short-lived

nudibranch species, with sub-annual life cycles, has been found to be strongly dependent

2

on seasonal peaks of temperature and dietary resources available in an area.

Nudibranchs that are long-lived, with annual or biannual life cycles, have food available

year round, leading to the assumption that they are not limited by food resources (Aerts,

1994). This suggests that the distribution of long-lived nudibranchs is dependent on

abiotic and other biotic factors. Larval supply is thought to be the key to determining adult

population dynamics of marine organisms (Levin, 2006). Marine protected areas (MPAs)

have provided a means of assessing ecosystem function, larval dispersal, connectivity

and resilience in a number of marine ecosystems (Babcock et al., 1999; Levin, 2006).

Understanding the dispersal mechanisms of organisms assists scientists in placement of

MPAs (Levin, 2006).

1.1 Nudibranchs

1.1.1 Family Characteristics

There are over 120 different families of nudibranchs, with new species being either

sighted or described monthly (“World Register of Marine Species,” 2014). Each family is

defined by unique characteristics relating to defence mechanisms, methods of dispersal,

life history stages, food specialisation, habitat preference, regionality and colouration. For

example, nudibranchs from the Suborder Aeolidacea have developed a defence

mechanism that is derived from the food they eat. After feeding on cnidarians aeolid

nudibranchs accumulate the ingested nematocysts into their own tissues for defence as

they lack the protective shells of other gastropods (Fogg-Matarese, 2009; Hoover et al.,

2012).

1.1.2 Distribution

Nudibranchs are important components of rocky intertidal and sub-tidal communities

(Todd, 1981). Biotic and abiotic factors both play a role in the dispersal and distribution of

nudibranch species. The majority of nudibranchs are benthic invertebrates relying on

3

abiotic conditions in their environment for geographic dispersal (Garcia and Bertsch,

2009). Biotic factors that influence nudibranchs include but are not limited to: presence of

settlement hosts, chemical cues from prey items and abundance of food; abiotic factors

that influence nudibranchs include temperature and current (McCuller, 2012).

Nudibranchs are found in marine habitats all around the world and are generally well

represented from equatorial to polar regions (Garcia and Bertsch, 2009). Biological

diversity tends to increase from polar to tropical regions, a typical characteristic of marine

organisms (Garcia and Bertsch, 2009)

1.1.3 Habitat and Feeding

Nudibranchs have been principally found in habitats consisting of loose rocks and coral

rubble, shoreward of fringing reefs (Kay and Young, 1969). Generally nudibranchs exist in

habitats where there are ample prey items (Lambert, 1991). Nudibranchs feed on a range

of marine organisms including ascidians, sponges, bryozoans, tunicates, corals, hydroids

or sea anemones (Todd, 1981; Martin et al., 2006). Studies of feeding behavior exhibited

by nudibranchs have revealed that segregation does occur when more than one species

is found in the same area. Lambert (1991a) showed that food availability was the main

cause for segregation between species; the spread of food in an area was the

determining factor as to where the different species of nudibranch could be found.

Stability of nudibranch populations has been linked to the stability of prey organisms. Prey

types such as soft corals and sponges have been determined to be available more

consistently over the year compared to bryozoans and hydroids that are seasonally

variable. Nudibranchs with sub-annual life cycles are more likely to feed on seasonally

variable prey items, with annual and biannual species of nudibranch more likely to feed on

temporally stable, encrusting prey organisms (Todd, 1981). Aeolid nudibranchs, including

Hermissenda crassicornis (Hoover et al., 2012), Cratena pilata (Fogg-Matarese, 2009)

and Cratena peregrine (Aguado and Marin, 2007) are known to be associated with

4

cnidarians (such as scyphozoan polyps) and have developed a chemical in their mucus

that inhibits the discharge of the stinging nematocysts, incorporating these cells into their

own tissues as a defense mechanism (Fahey and Garson, 2002; Martin et al., 2006;

Aguado and Marin, 2007; Hoover et al., 2012).Hoover et al. (2012) suggested that

nudibranch species that consume cnidarians, polyps and hydroid species have the

potential to control jellyfish blooms, though further studies are necessary.

1.1.4 Life History

The three main ecological life cycle groupings of nudibranchs; sub-annual, annual and

biannual, were identified by (Todd, 1981). Sub-annual species are generally small,

cryptically coloured and characterised by unstable populations that fluctuate in abundance

over short periods of time (Todd, 1981). Morphology and temporal stability of nudibranch

life cycles has been linked to the stability of prey organisms of each species. Annual

species complete only a single generation over the period of one year, often exhibiting

striking colourations compared to the substrate they are found on. A large majority of

nudibranchs fall into the annual life cycle category and tend to feed on stable encrusting

prey types such as corals, bryozoans and hydroids. Nudibranchs with an annual lifecycle

usually survive three to four months post-spawning before mortality occurs (Todd, 1981).

The prey of biennial nudibranch species largely consists of, but is not limited to, stable

colonial organisms such as octocorals and sponges (Todd, 1981; García-Matucheski and

Muniain, 2011). Access to stable food sources year round is thought to be linked to

extended life periods and larger sizes of individual species.

A wide range of larval forms exist within the Nudibranchia, ranging from direct

development to short or long term plankton; namely planktotrophic or lecithotrophic

development (Todd, 1981; Hadfield, 1987). Larvae with direct development have

eliminated the need for free-living larval forms compared to planktotrophic larvae that

have an extended pelagic feeding phase lasting for several weeks (Todd, 1981).

5

Lecithotrophic larvae are only in the pelagic phase for a few hours to days and do not

feed (Todd, 1981). Thompson (1958) discovered that larvae of the nudibranch, Adalaria

proxima metamorphose only in the presence of living bryozoans of the species Electra

pilosa, when the larvae can ‘smell’ the live bryozoans even though adults of this species

have been recorded feeding on at least three other species of bryozoans. Metamorphose

of larvae occurs during the substrate searching phase, with larvae being able to search

for up to two weeks for suitable substrate to settle upon (Thompson, 1958). General

flattening of the body, casting of shell, casting of operculum and the inversion and spread

of the mantle fold are main external changes that occur during metamorphosis. As with

many other marine planktonic larvae, nudibranchs respond to a number of chemical and

physical cues from their prey items to metamorphose, settle and complete their life cycle.

Studies have shown that nudibranch larvae post hatching have an upwards swimming

stage that is quite rapid, occurring regardless of the light source (Hadfield, 1987).

Investigations into the effect this has on distribution of larvae via currents in an area have

yet to be carried out. In the majority of nudibranch species, one mating provides enough

sperm for several spawnings (Hadfield, 1987). Individuals that are isolated after mating

may continue to lay eggs, though fertilisation may not occur for up to 3-4 egg masses

(Hadfield, 1987).

1.1.5 The Leeuwin Current

The Western Australian marine environment is diverse and unique, with the world’s only

southern flowing eastern boundary current, the Leeuwin Current. The Leeuwin Current is

responsible for the majority of larval dispersal and planktonic movement along the west

Australian coastline (Hutchins and Pearce, 1994; Waite et al., 2007). The Leeuwin

Current extends from the Northwest Shelf and continues along the continental shelf

around Cape Leeuwin, and eastward across the Great Australian Bight (Figure 1.1.5)

(Cresswell 1991; 1996). This current supplies the high latitudes of western and southern

Australia with warm water. In contrast, other eastern boundary currents in the southern

6

hemisphere (such as the Humboldt Current and the Benguela Current) carry cool, nutrient

rich waters northwards (Morgan and Wells, 1991; Pearce, 1991; Caputi et al., 1996). The

warm waters of the Leeuwin Current allow tropical species of marine life to venture and

settle further south and survive in temperate waters (Pearce et al. 2011). Eddies and

gyres, varying in size from 10 km to 100 km wide, bud off from the Leeuwin Current and

have been found to enhance planktonic biota abundance and diversity in regions where

eddies are formed (Feng et al., 2010; Holliday et al., 2012) .

The Abrolhos Islands, located on the edge of the continental shelf, lie directly in the path

of the Leeuwin Current. It is believed that large eddies have a major influence on the flora

and fauna inhabiting this region (Phillips and Huisman, 2009). Geraldton is inshore, not on

the edge of the continental shelf, and therefore the Leeuwin Current does not have a

direct impact in this area (Wells and Bryce, 1993). During the winter months the Leeuwin

Current tends to flow closer to the coastline and in the summer months the flow moves

offshore, onto the edge of the continental shelf (Feng et al., 2009). The Capes Current, an

equator-ward current is the dominant current inshore along the Western Australian

coastline during these summer months (Gersbach et al. 1999; Pearce and Pattiaratchi

1999; Pattiaratchi and Woo 2009). The Capes Current is a cool, higher salinity, seasonal,

wind driven flow of relatively nutrient rich water originating in the Cape Leeuwin region

extending to the Abrolhos Islands (Gersbach et al., 1999; Pattiaratchi and Woo, 2009). It

is believed that the Capes Current, like the Leeuwin Current has a significant influence on

seasonal migration and spawning patterns of numerous fish species (Gersbach et al.,

1999).

7

Figure 1.1.5: The surface currents off southwestern Australia. The Leeuwin Current flows year round, being the strongest in winter and is marked by the broad grey arrow. The Capes Current is marked by the long black arrow along the continental shelf and is driven by summer southerly winds. There are two eddies that have separated from the Leeuwin Current. The Abrolhos Islands are located within the path of the Leeuwin Current, compared to Geraldton which receives waters from the Capes Current. Adapted from Cresswell and Domingues (2009)

1.2 Climate Change

Ocean acidification and global warming are altering the marine environment, with sea

surface temperatures slowly increasing and estimated to reach between 1°C and 4°C

higher than the current maximum by the end of the century (IPCC, 2007). With climate

change effects forecast to drive organisms towards the polar regions, away from the

equator (Perry et al., 2005). Strong evidence of this has already been documented, with

8

the sea urchin Centrostephanus rodgersii expanding its natural range pole-ward from

New South Wales to Tasmania (Johnson et al., 2011). Marine ecosystems and the

physical environment of Western Australia are considered to be sensitive environments,

susceptible to climate variability (Feng et al., 2009). Regional projections show the

Leeuwin Current will experience low to medium effects from climate change, with experts

now suggesting focus be turned to conservation responses to increase resilience of

marine ecosystems (Feng et al., 2009).

1.2.1 Known Climate Change Impacts

The effects of climate change are visible today, with climate driven phenomena resulting

in large changes in marine ecosystems. Chavez (2012) discussed dramatic shifts in fish

abundance along the coast of Peru, which can be linked to an event involving the polar

ice caps. The ice caps expanded causing the InterTropical Convergence Zone (ITCZ)

(sometimes referred to as the meteorological equator) to shift southwards. This halted the

main driver of nutrients in the Pacific Ocean, (the Walker Circulation) causing the now

abundant fish populations to be barely evident. When the conditions in the Pacific Ocean

became warmer again, the wealth of fish populations returned. Research has shown the

East Australian Current has extended its range southwards along the eastern coast of

Australia with effects of the current now seen in Tasmania. Johnson et al. (2011)

discussed how a better understanding of climate change effects between individual taxa

and interactions between species is critical for managing future climate change

projections.

A warm water event occurred along the west Australian coast in the austral summer of

2010/2011 (Pearce and Feng, 2013; Caputi et al., 2014). This event was associated with

one of the strongest La Nina events on record, with temperatures of the Leeuwin Current

reaching 5°C higher than equivalent latitudes of other southern hemisphere eastern

boundary currents (Feng et al., 2013; Pearce and Feng, 2013). Benthic invertebrates that

9

were affected by this heat wave included abalone (Haliotis roei), with a complete mortality

of stocks north of the Murchison River (Kalbarri), and lobster (Panulirus cygnus)

mortalities at the Abrolhos Islands.

1.2.2 Postulated Climate Change Impacts

Species of marine invertebrates endemic to an area are under the greatest threat from

climate change (Hughes, 2003). O’Hara (2002) suggests that a portion of species that are

endemic to a region may become locally extinct with temperature increases. O’Hara’s

study focused on marine invertebrates and their distribution along the Victorian coastline

predicting extinctions of echinoderms, gastropods and decapods with 1-2 °C rises in

seawater temperatures.

Researchers are predicting jellyfish will take-over our marine environments in the future.

Effects from climate change enable jellyfish to grow faster, increasing population size

whilst jellyfish predators are being overfished, leaving the populations to flourish

(Richardson et al., 2009).

1.3 Worldwide Nudibranch Diversity

Limited studies have been conducted on nudibranchs, making them relatively mysterious

organisms. Although comprehensive studies have examined the chemical aspects of

nudibranchs and their ecology, there is limited literature on depth associations of different

nudibranch families, species abundance in specific regions, factors that affect distribution

and abundance, or habitat and food preferences. Worldwide studies on nudibranchs are

equally limited, although Bennett (2013) compiled a list of opisthobranch species

identified in different regions around the world (Table 1.3).

10

Table 1.3: Total number of opisthobranchs found at various locations around the world, in both northern and southern hemispheres (Bennett, 2013).

Locality Total Sampling Period

Average Latitude

No. Species

Eastern Arctic Unknown 71°N 5

Great Britain Unknown 53°N 133

Western Arctic Unknown 51°N 37

California 40 years 34°N 212

Caribbean 25 years 22°N 329

Hawaii Unknown 20°N 430

Guam Several years 13°N 474

Philippines Unknown 12°N 563

Panama Unknown 10°N 218

Tanzania Unknown 7°S 258

Papua New Guinea >6 years 10°S 646

Northern Great Barrier Reef (Aust.) 5 years 14°S 158

Madagascar Unknown 20°S 168

Southern Great Barrier Reef (Aust.) 32 years 23°S 261

Sunshine Coast (Aust.) 8 years 26°S 501

Victoria (Aust.) 52 years 39°S 336

Temp (South Africa) Unknown - 124

New Zealand 50 years 41°S 162

11

1.4 Western Australian Nudibranch Diversity

There is a gap in the knowledge of opisthobranchs, including nudibranchs, not only in

Western Australia but Australia wide (Table 1.4). Studies which have been completed on

nudibranchs in Australia include assessment of rarity in Queensland (Benkendorff and

Przeslawski, 2008), chemical associations by (Garson and Chem, 2004) and (Yong,

Salim, and Garson, 2008). Bennett (2013) focused on the diversity, distribution,

abundance and feeding ecology of opisthobranchs at Coral Bay, Ningaloo Reef, Western

Australia and compiled diversity estimates from localities in Western Australia and their

relative survey duration (Table 1.4). It was noted that the survey duration for studies

carried out before the year 2000 were not specifically opisthobranch targeted surveys.

These studies were carried out by the Western Australian Museum and focused on

collecting all molluscan species, not specifically nudibranchs. The Western Australian

Museum is currently in the process of collecting samples of opisthobranchs from the

Kimberley region, Rowley Shoals and the Abrolhos Islands to ascertain accurate species

identifications, taxonomic information and genomics of species. The results from this

study will not be available in time to be included in this paper (pers. comm. Nerida Wilson,

2014). An Honours project is currently in progress focusing on the south west of Western

Australia looking at the abundance and diversity of nudibranch species at the Busselton

Jetty; the results from this study are not available for inclusion in this paper. The Midwest

of Western Australia is lacking in published literature on nudibranchs; their behaviors,

abundance, species richness, depth associations and benthic habitats with which they are

associated.

12

Table 1.4: Comparison of diversity estimates of opisthobranchs for surveys this survey and surveys undertaken in similar localities. Adapted from Bennett (2013)

Location

Surveyed

Year Survey Duration No. Species

Dampier

Archipelago

1998

1999

156 hours 90

Montebello Islands 1993 135 hours 63

Murion Islands &

Exmouth Gulf

1996 72 hours 54

Coral Bay 2013 60 hours 56

Bernier and Dorre

Islands

1995 66 hours 55

Abrolhos Islands** 2014 26 hours 16

Geraldton** 2014 8 hours 7

**Results from this study

1.5 Aims of This Study

The Abrolhos Islands is a unique area located in the Midwest of Western Australia,

supporting a mixture of tropical and temperate organisms (Phillips and Huisman, 2009;

Scheffers et al., 2012). There has been limited research carried out in the Midwest region

on nudibranchs, which includes Geraldton and the Abrolhos Islands; this has provided the

motivation for this study. Four main areas were the focus of this study: inshore Geraldton

and offshore at the Abrolhos Islands across the three island groups: Wallabi, Easter and

Pelsaert.

The overarching aim of this research is to collect quantitative information from a range of

locations within the Midwest region of Western Australia and establish a biogeographical

baseline for the nudibranchs of this region. Specifically, the ecosystems they inhabit,

species diversity, overall abundance and ecological processes that influence their

13

distribution and the direction of future research. The Midwest region is a transition zone

with critical overlap between tropical and temperate climate conditions; climate change-

induced shifts are expected to occur in this region and the collection of baseline data can

be used to monitor these shifts overtime.

The major aim of this study is to document baseline data for future long term monitoring

programs, accounting for temporal and spatial variation in species abundance. The main

focus is on diversity, species richness and abundance of nudibranchs at the Abrolhos

Islands and Geraldton. Investigations into habitat substrate, depth preference and

connectivity will be explored. Site specific data will be recorded for each site including

depth, water temperature, habitat use and activity undertaken by the individual

nudibranch.

14

2.0 METHODS

2.1 Area Description

Surveys for nudibranchs were conducted at Geraldton (28°45.5399 S; 114°37.0820 E)

located in the Midwest of the Western Australian coastline; and the Houtman Abrolhos

Islands located on the edge of the continental shelf, 65-70 km to the north-west of

Geraldton (Figure 2.1.1) (Phillips and Huisman 2009; Scheffers et al. 2012). The Houtman

Abrolhos Islands (for the purpose of this paper referred to as the Abrolhos Islands) are

comprised of 122 islands in three distinct groups: Wallabi Group, Easter Group and

Pelsaert Group (Scheffers et al., 2012) (Figure 2.1.2). These islands form one of the most

complex high latitude coral reef systems in the world (Phillips and Huisman 2009).

Sample sites were randomly spread across the three groups, Easter Group (28°42 S;

113°47 E), Pelsaert Group (28°52 S; 113°57 E) and Wallabi Group (28°27 S; 113°43 E)

(Figure 2.1.2; a detailed layout of the sampling sites at each group is included in Appendix

2).The Leeuwin Current has noticeable impact on environmental parameters across the

Abrolhos Island groups and distinguishing the Islands from inshore habitats at Geraldton

(Phillips and Huisman 2009). Geraldton is inshore, not on the edge of the continental shelf

therefore the Leeuwin Current does not have an impact in this area.

15

Figure 2.1.1: The location of study sites, Geraldton and the Abrolhos Islands, in relation to Western Australia Adapted from (Caputi et al., 1996).

16

Figure 2.1.2: Geraldton and the three Abrolhos Islands study sites, showing their location relative to each other (Google Earth, 2014)

2.2 Environmental Description

2.2.1 Wind

The winds at both Geraldton and the Abrolhos Islands have a similar seasonal wind

pattern throughout the year. The Abrolhos Islands experience greater wind strengths with

a mean wind speed in winter of 23.4 km h-1 and summer 31 km h-1 compared to Geraldton

wind strengths of 15.8 km h-1 and 24.8 km h-1 respectively (Pearce, 1997; Phillips and

Huisman, 2009).

2.2.2 Swell

Geraldton has a persistent, low to moderate wave energy regime with dominant swell

from the south to south-west (Hegge et al., 1996). Persistent swell waves are present at

17

the Abrolhos Islands generated by prevailing south-westerly winds from the Southern

Ocean (Scheffers et al., 2012). Swell has a mean wave height of 1.2 m approaching from

the south and west for the majority of the time (Collins et al., 1996; Scheffers et al., 2012).

The south-westerly reef margins absorb the full force of wave impacts, with the south-

easterly reef edge attracting refracted swell and effects from wind waves (Collins et al.,

1996).

2.2.3 Current

The Leeuwin Current is the dominant current that runs along the Western Australian

coastline and is summarised by Hatcher (1991) as being a narrow (<200 km), shallow

(<200 m) stream of water of tropical origin which flows southwards at relatively high

velocities (0.1-0.4m s-1) along the western continental slope of Australia. Studies have

shown that there is little direct influence of the Leeuwin Current near the coast (Phillips

and Huisman 2009); however being situated of the edge of the continental shelf, the

Abrolhos Islands are directly in the path of the Leeuwin Current. Large eddies have been

known to form between the islands groups creating small northward flowing currents

(Phillips and Huisman 2009).

2.2.4 Water Temperatures

The Western Australian Department of Fisheries have collected long-term time-series sea

temperature data for the Abrolhos Islands. Mean temperatures measured at Rat Island

(Easter Group) ranged from 19.5°C in August to 23.3°C in March. Mean sea temperatures

at Dongara, located on the coast 65 km south of Geraldton ranged from17.5°C in July to

23.9°C in February (Pearce 1997; Pearce et al. 1999; Phillips and Huisman 2009). The

effect of the Leeuwin Current is particularly evident at the Abrolhos Islands during the

winter months, maintaining ocean temperatures 2°C warmer than near the coast.

18

2.2.5 Salinity

Salinity at the Abrolhos Islands ranged from 35.37ppm in July to 35.74ppm in January.

Dongara salinities ranged from 35.40ppm in July to 36.34ppm in February; Dongara

salinities are similar to those found in Geraldton waters (Phillips and Huisman 2009). High

salinity levels inshore can be attributed to evaporation in summer months whilst offshore

the low salinity levels during winter months are caused by the Leeuwin Current (Phillips

and Huisman 2009).

2.3 Habitat Description

In March 2014 pilot surveys were conducted at the Abrolhos Islands and Geraldton to

determine the occurrence of nudibranch species on different habitat substrates.

Nudibranchs were found mainly in habitats that consisted of coral rubble overgrown with

seaweeds; research efforts were therefore focused on sites that consisted of this habitat

type. Sampling methods were designed to focus on benthic nudibranchs in both shallow

and deep water habitats to gain information on the diversity and distribution of

nudibranchs at Geraldton and the Abrolhos Islands.

2.4 Site Selection

Sites were randomly selected by looking at a nautical chart of the Abrolhos Islands. For

each of the four sub-regions sampled 30 shallow sites were selected at random and 30

deep sites were selected at random; these sites matched the habitat description criteria

as closely as possible. The sites were numbered from 1 to 30 and placed into a random

number generator. The first four numbers were then chosen as sampling sites. The

numbers were regenerated each time when choosing sampling sites for each sub-region.

19

2.5 Survey Methods

Sampling was undertaken seasonally, to obtain a quantitative measure of nudibranch

abundance at deep and shallow sites in the months of April, June and August. 15 m

transects were set up using rope, ballast, sinkers and floats. The floats and ballast were

positioned at 0 m, 7 m and 15 m along the transect line. The transect line was deployed at

each of the sample sites; researchers then proceeded to swim along each side of the

transect using SCUBA (Figure 2.5.1), covering an area of 60 m2 (2 m either side of the

transect line). When a nudibranch was found several photographs were taken in situ, both

macro and at a distance, to be able to accurately identify each individual. These images

were also used to identify the substrate the nudibranch was observed on; habitats were

recorded as one of the following eight categories, adapted from Bennett (2013): rocky reef

(R), crustose coralline algae (CA), macroalgae (MA), sessile organisms including

spongers (S), Corals (C), sand/coral rubble (S/R), limestone (L) and unidentified (U). The

activity of each individual nudibranch was determined using the images captured. Two

depth categories were examined in this study: shallow sites were in the range of 1–2 m in

depth and deep sites ranged from 5 m to 8 m. Four activity categories were identified:

mating, stationary, moving and laying eggs. Nudibranch individuals that were in contact

with another nudibranch were deemed to be mating. It was assumed that nudibranchs

that were stationary were feeding. Each of the sample sites was given a unique site name

corresponding to which location it can be found, for example site E14 represents a site

that is in the Easter Group that is shallow sample site number 4 or W52 represents a site

that is in the Wallabi Group that is a deep sample site number 2 (See Appendix 2).

20

Figure2.5.1: Divers in the field searching for nudibranchs along the transect line

2.6 Species Identification

Nudibranchs were identified from photographs taken in- situ using Wells and Bryce

(1993), Coleman (2001) and Debelius and Kuiter (2007) as well as using information on

online forums such as the Australian Museum’s Online Seaslug Forum (Rudman, 2010)

and Nudibranchs of the Sunshine Coast, Queensland and Tasmania, Australia (Cobb and

Mullins, 2014). Several Chromodoris species individuals of the blue, black, orange and

white colouration look quite similar and hard to accurately identify with certainty to species

level. Species exhibit characteristics that constantly overlap. After consultation with

taxonomic experts it was decided that if the individual had a punctuate pattern with either

white pigments on the mantle flap it belonged to Chromodoris annae but if it was found to

have blue on the mantle flap it belonged to Chromodoris westraliensis. If there was no

punctate pattern at all it most likely belonged to Chromodoris sp. 24.

Gary Cobb, a nudibranch expert and creator of the webpage Nudibranchs of the Sunshine

Coast, Queensland and Tasmania, Australia, was consulted for his opinion on several of

21

the Chromodoris species that were similar. Nerida Wilson, Senior Research Scientist of

the Molecular Systematic Unit at the Western Australian Museum was also consulted,

confirming all of the nudibranch identifications and recommended that gene sequencing

take place for accurate species level identifications for the individuals that cannot be

confidently identified. This information is, at this stage being processed and is currently

still unpublished. Due to a lack of resources, individuals that could not be identified to

species level were identified as near as possible to a particular species and labeled

accordingly; e.g. Chromodoris cf. annae.

2.7 Statistical Analysis

2.7.1 Species and Abundance

Basic statistical analysis of data was performed using Microsoft Excel 2007 and IBM

SPSS v. 21. Comparison of abundance and species abundance was performed using

IBM SPSS v 21. All assumptions required for undertaking the statistical tests were

assessed and met.

Species are considered rare if they persist in low abundances and are restricted to a few

specialised sites (Benkendorff and Przeslawski, 2008). The use of the quartile cut-off

provides a standardised method to asses rarity in rocky shore invertebrates (Benkendorff

and Przeslawski, 2008) Use of the rarity scale helps target species with lower than

average abundances for more in-depth studies (Benkendorff and Przeslawski, 2008). A

scale of rarity was derived from Benkendorff & Przeslawski (2008) based on one of the

three assessment measures, numerical rarity (Table 2.7.1). The proportion of nudibranchs

was used to rank occurrence into quartiles

22

Table 2.7.1: Rarity scale used to determine occurrence of nudibranchs at the Abrolhos Islands and Geraldton. Adapted from Benkendorff & Przeslawski (2008).

Abundant ≥ 30 individuals observed over the survey sites

Common 8-29 individuals observed over the survey period

Uncommon 2-7 individuals observed over the survey sites

Rare Single observation of an individual with unpredictable

occurrence across survey sites

2.7.2 Species Diversity and Evenness

The Shannon-Weaver index of diversity (H’) was used to explore differences in species

richness between sites and depth of sites.

Where pi is the proportion of individuals of each species to the total number of individuals

(Shannon and Weaver, 1963).

Species evenness was determined using Pielou’s Evenness Index:

23

H’ is the Shannon Weaver diversity index and H’max can be determined by ln(S), where S

is the total number of species. H’max is the theoretical maximum values for H’ if all species

were equally abundant (Pielou, 1966).

2.7.3 Connectivity

Species connectivity was determined using PRIMER v 6.1 (Primer-E Pty Ltd).

24

3.0 RESULTS

In total, 89 dives were made over the duration of this study, with an average dive time of

30 minutes and an accumulated overall bottom time of 23 hours and 14 minutes. Two of

the deepest dives of the study took place in the Wallabi Group, reaching 8.7 m and 8.5 m

at sites W51 and W54 respectively (See Appendix 2.4). The shallowest average dive was

to 1.5 m occurring at 11 of the sample sites at two of the shallow sites in each sampling

location; a summary of depth and other site details can be found in Appendix 1.

3.1 Species and Abundance

A total of 296 individual nudibranchs were visually observed and photographed across 89

separate dive surveys over the study period from April to August 2014. 148 individuals

were identified from both shallow and deep sample sites across the four different sub-

regions. A total of 17 different species of nudibranch were found at the shallow sites

across all four sub-regions and 12 different species across the deep sites. Of the total

species found six were present at both shallow and deep sampling sites. Geraldton had

11 individuals of six species found at the shallow sites and five individuals of two species

at the deep sites (Figures 3.1.1 and 3.1.2). The Easter Group had 71 individuals of 12

species found at the shallow sites and 65 individuals of six species at the deep sites. The

Wallabi Group had 36 individuals of five species over the shallow sites and 38 individuals

of six species over the deep sites. The Pelsaert Group had 30 individuals of ten species

across the four shallow sites and 40 individuals of seven species found across the four

deep sample sites.

25

Figure 3.1.1: Total number of individual nudibranchs found in each of the survey sub-regions at two depths over an area totaling over 5 km

2

Figure 3.1.2: Total number of species of nudibranchs found in each of the survey sub-regions at two depths over an area totaling over 5 km

2

0

10

20

30

40

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Geraldton Easter Wallabi Pelsaert

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Geraldton Easter Wallabi Pelsaert

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Of the three sampling trips the first trip was the most successful with researchers locating

a total of 111 nudibranchs, 52 individuals over the 17 shallows sites and 59 individuals

over the 14 deep sites. The second and third sampling trips resulted in 82 and 103

individual nudibranchs respectively being located and photographed. Each sampling trip

was carried out in a different season; the first trip in autumn, the second trip in winter and

the third trip in spring. A total of 19 different species were identified; Table 3.1.3 is a

complete list of nudibranch species that were identified during the study, their respective

families, authority and occurrence according to the rarity scale (see Table 2.7.1).

Table 3.1.3: Complete list of nudibranch species found over the duration of the study at Geraldton and the Abrolhos Islands, 2014

Family Species Name Authority Occurrence

Aegiridae Notodoris citrina Bergh, 1875 Common

Chromodorididae Chromodoris annae Bergh, 1877 Common

Chromodoris cf. annae

Common

Chromodoris cf. sp. 24

Common

Chromodoris cf. westraliensis

Common

Chromodoris westraliensis O'Donoghue, 1924 Abundant

Chromodoris sp. 24

Abundant

Glossodoris atromarginata Cuvier, 1804 Rare

Glossodoris hikuerensis Pruvot-Fol, 1954 Rare

Mexichromis cf. mariei Rare

Dendrodorididae Dendrodoris fumata Ruppell & Leuckart, 1831 Rare

Discodorididae Atagema intecta Kelaart, 1858b Uncommon

Jorunna funebris Kelaart, 1858 Uncommon

Gymnodorididae Gymnodoris citrina Bergh, 1875 Uncommon

Gymnodoris sp. Rare

Phyllidiidae Phyllidiella pustulosa Cuvier, 1804 Uncommon

Polyceridae Crimora lutea Baba, 1949 Rare

Tritoniidae Marionopsis dakini O'Donoghue, 1924 Uncommon

Tritoniopsis elegans Andouin, 1826 Uncommon

27

3.2 Family Level Analyses

The 19 species of nudibranch found during the study came from 13 different genera in

eight families (Table 3.1.3). The family Chromodorididae was the dominant family, with a

total of 268 individuals in three genera; Aegiridae had 8 individuals, Tritoniidae and

Discodorididae had 5 and 6 individuals respectively from two different genera.

One species of nudibranch could only be identified to genus level as it is currently not

described, and is not in any published identification book; additional information is

required for taxonomic placement (Figure 3.2.1). The most abundant species found

overall was Chromodoris westraliensis (n=155). The second most abundant species

across the study regions was Chromodoris sp. 24 (n=48). Several variations of

Chromodoris sp. 24 were found during the study, with varied colouration and patterns;

hence the decision to identify 11 individuals as Chromodoris cf. sp. 24. (Figure 3.2.2).

Chromodoris cf. annae (n=27), Chromodoris cf. westraliensis (n=17), Chromodoris cf. sp.

24 (n=10) concluded the top five nudibranch species found during the study. Chromodoris

annae and Notodoris citrina both had 8 individuals found.

28

Figure 3.2.1: Unidentified species found during this study, Gymnodoris sp.

Figure 3.2.2: Two alternative versions of Chromodoris cf. sp. 24 that were found over the duration of this study.

29

3.3 Total Abundance Analyses

A T-test was performed to investigate whether there was a difference in the mean number

of individuals in the shallow and deep sampling sites. No significant difference was found

between the mean number of individuals per transect at shallow (mean = 2.90, SE = 1.23)

and deep sites (mean = 3.58, SE = 1.34) (α = 0.05, t29 = 2.05, p-value = 0.48), the number

of nudibranchs at deep and shallow sites were the same. The largest number of

individuals per transect was found at the Easter Group (mean = 22.5, ± 0.77 SE) followed

by the Wallabi Group (mean = 12.33, ± 0.73) and the Pelsaert Group (mean = 11.8, ±

0.79 SE), with the lowest recorded number of individuals per transect at Geraldton (mean

= 3.2, ± 0.32 SE).

There was a significant difference in the mean number of individuals per transect at the

four sites (ANOVA: α=0.05, F(3,89)=5.21, p-value=0.002). To investigate if Geraldton was

the determining factor for the significant difference in the initial ANOVA analysis, the

analysis was run again; although this time Geraldton was excluded. The second ANOVA

resulted in a significant difference (α=0.05, F(2,71)=3.83, p-value=0.026). The mean (± SE)

number of nudibranchs per transect found across each sub-region varied markedly

(Figure 3.3.1), with a mean of 0.9 (± 0.25) for the shallow sites and a mean of 1.25 (±

0.25) for the deep sites at Geraldton. At the Abrolhos Islands, the Easter Group sites had

the highest mean number of nudibranchs per transect over the duration of the study at

both shallow and deep study sites, with a mean of 5.8 (± 0.33) and 5.4 (± 0.76)

respectively. The Wallabi Group had a mean of 3.0 (± 0.09) nudibranchs across the

shallow sites and a mean of 3.2 (± 1.04) nudibranchs across the deep sites per transect.

The Pelsaert Group had a mean of 2.6 (± 0.28) nudibranchs across the shallow sites and

a mean of 3.3 (± 0.96) individuals across the deep sites per transect. The deep sample

sites at the Easter Group, Wallabi Group and Pelsaert Group showed a large variation in

numbers per transect over the three sampling trips, resulting in a greater standard error

30

compared to the shallow sites. The shallow survey sites at the Wallabi Group resulted in

the least amount of variability.

Figure 3.3.1: The average nudibranchs found each study trip at each study site comparing the variation between shallow and deep study sites per transect

3.4 Total Species Analyses

To investigate whether there was a difference in the mean number of species in shallow

vs. deep sites a T-test was performed. No significant difference was observed between

the mean number of species at shallow (mean = 1.63, SE = 0.372) and deep sites (mean

= 1.54, SE = 0.078) per transect, (α = 0.05, t29 = 0.22, p-value = 0.826). A significant

difference in the mean number of species per transect between the four study sites was

observed using ANOVA (α = 0.05, F(3,89) = 6.43, p-value = 0.001). To determine if

Geraldton was the driving factor for the significant difference result the analysis was

performed again excluding Geraldton; a significant difference was observed between the

three Abrolhos Island sites (ANOVA: α=0.05, F(2,71)=5.18, p-value=0.008). The largest

0.0

1.0

2.0

3.0

4.0

5.0

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Geraldton Easter Group Wallabi Group Pelsaert Group

Me

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31

number of species per transect was found at the Easter Group (mean = 10, ± 0.31)

followed by the Wallabi Group (mean = 6.7, ± 0.26 SE) and the Pelsaert Group (mean =

5.5, ± 0.19), and lastly the lowest recorded species per transect was at Geraldton (mean

= 2.4, ± 0.24 SE).

The mean number of nudibranch species found across each sub-region varied with

Geraldton having a mean of 0.6 (± 0.21) for the shallow sites and a mean of 0.8 (± 0.25)

for the deep sites per transect (Figure 3.3.2). In the Abrolhos Islands region, the Easter

Group had the highest mean number of species of nudibranchs per transect over the

duration of the study at both shallow and deep study sites with a mean of 2.9 (± 0.14) and

2.1 (±0.18) species respectively. The Wallabi Group had a mean of 1.7 (± 0.24) species of

nudibranchs per transect for both shallow and deep sites. The Pelsaert Group had a

mean of 1.4 (± 0.11 SE) across the shallow sites and 1.3 (±0.07) species across the deep

sites per transect.

Figure 3.3.2: The average species of nudibranchs found each study trip at each study site comparing the variation between shallow and deep study sites per transect

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Geraldton Easter Group Wallabi Group Pelsaert Group

Me

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32

3.5 Interactions

To explore interactions between sub-region and depth for individual counts and species

counts, two factorial ANOVAs were carried out. Sub-region was a significant factor for

number of individuals per transect and depth was not significant (F(3,89) = 0.08, p-value =

0.778) (Figure 3.5.1). An interaction was observed between depth and sub-region but was

found to be not significant (F(3,89) = 0.11, p-value = 0.952). For the number of species

region was significant and depth was not significant (F(3,89) = 0.58, p-value = 0.448)

(Figure 3.5.2). The interaction between depth and region was not significant (F(3,89) = 0.62,

p-value = 0.601).

Figure 3.5.1: Results from factorial ANOVA with the mean number of individual nudibranchs found at the different sites, compared with depth.

33

Figure 3.5.2: Results from factorial ANOVA with the mean number of species of nudibranchs found at the different sites, compared with depth.

3.6 Species Diversity and Evenness Indices

Of the four sub-regions sampled, Geraldton had an overall total of six species across all

shallow sites and an overall total of two species across the deep sites. The Abrolhos

Islands had an overall total of 14 species across all shallow sites and an overall total of

nine species across all deep sites.

The Shannon-Weaver index of diversity (H’) and Pielou’s evenness index (J’) were

calculated for several different factors across the study. Firstly the diversity and evenness

of all species found was calculated, generating a diversity index of 1.71 and an evenness

index of 0.58 for the Midwest region of Western Australia.

34

Species diversity and evenness were greater inshore at Geraldton (H’ = 1.93, J’ = 0.93),

than at the Abrolhos Islands (H’ = 1.62, J’ = 0.10). Diversity and evenness for depth

variations was greater at shallow sites (H’ = 1.97, J’ = 0.47), than at the deep sites (H’ =

1.32, J’ = 0.90). A species diversity index was calculated for all of the survey sites across

the shallow and deep sampling sites (Figure 3.2.1). The Easter Group (H’ = 1.90, J’ =

0.76) and the Pelsaert Group (H’ = 1.90, J’ = 0.82) had the equal greatest diversity across

shallow sites compared to Geraldton (H’ = 1.59, J’ = 0.89) and the Wallabi Group (H’ =

0.92, J’ = 0.57) (Figure 3.6.1). The Pelsaert Group (H’ = 1.30, J’ = 0.67) had the greatest

diversity across deep sample sites followed by the Wallabi Group (H’ = 1.11, J’ = 0.62),

the Easter Group (H’ = 1.07, J’ = 0.60) and Geraldton (H’ = 0.67, J’ = 0.97).

Figure 3.6.1: Shannon Weaver diversity index for mean nudibranchs found across the two study regions

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

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Geraldton Easter Group Wallabi Group Pelsaert Group

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3.7 Connectivity

Bray-Curtis similarity cluster and Multi-Dimensional Scaling (MDS) plots were created to

explore the species abundance, diversity and depth preference between sample sites.

Geraldton is clearly different to the island groups, with distinct differences in species

abundance not only between sub-regions but between depths as well (Figure 3.7.1,

Figure 3.7.2). To better understand similarity in the Abrolhos Islands groups, Geraldton

was excluded from the MDS analysis in Figure 3.7.3. The similarity of individual sampling

sites was compared with two shallow sites from the Pelsaert Group having less than 20%

similarity compared to the other island group sampling sites.

Figure 3.7.1: Dendrogram of hierarchical clustering combining all sampled sites from March to August 2014, using group average linking of Bray-Curtis coefficient (Southern Group is referring to Pelsaert Group).

36

Figure 3.7.2: MDS analysis of nudibranch abundance at all sample sites showing depth as a factor.

Figure 3.7.3: MDS analysis of nudibranch abundance at the Island sample sites (excluding Geraldton) showing similarity with depth as a factor.

37

Whilst Figure 3.7.1 shows the grouped averages of abundance of all sites sampled,

Figure 3.7.4, shows the condensed group averages of abundance specific to depth

preference. There is a clear separation between Geraldton and the island sites in Figure

3.7.4 the Wallabi Group was found to have the most similarity between deep and shallow

sites compared to the Easter Group and the Pelsaert Group, which have the most

similarities between sites of the same depth. MDS similarity of island sampling sites,

excluding Geraldton to allow for clearer comparison, illustrated a similarity of 90%

between the Wallabi Group shallow and deep sampling sites, with the Easter and

Southern Group having 60% similarity (Figure 3.7.5). No sites were determined to be

more than 90% similar.

Figure 3.7.4: Dendrogram of hierarchical clustering of sub-regions sampled, defined by depth preference, using group average linking of Bray-Curtis coefficient (Southern Group is referring to Pelsaert Group).

38

Figure 3.2.5: MDS analysis and similarity clustering of all island sites (excluding Geraldton) (Southern Group is referring to Pelsaert Group).

3.8 Substrate Preference and Activity

Substrate type and activity of each nudibranch found was determined using field

observations and photographs taken at the time of observation. The majority of

nudibranchs were found on either rocky reef or macroalgae substrates, with moving being

the dominant activity at both shallow and deep sites (Figure 3.8.1). Shallow and deep

sites combined resulted in rocky reef and macroalgae being the overall dominant

substrate types (31.4%), followed by crustose coralline algae (14.5%), sand/coral rubble

(11.5%), sessile organisms (6.4%), unidentified (3.4%) and corals (1.3%). The activities of

each nudibranch were combined for the shallow and deep sites finding moving to be the

dominant activity (79.4%), followed by stationary (18.9%), mating (1.4%) and laying eggs

(0.3%). Out of the 6.5% of nudibranchs found on sessile organisms, 4% were classified

as stationary.

39

Figure 3.8.1: Percentage of individual nudibranchs combined of both shallow and deep sites and their respective activity compared to the substrate they were found inhabiting

40

4.0 DISCUSSION

4.1 Estimating and Comparing Diversity

Limited studies on nudibranch species diversity have been carried out in Western

Australia, with the Western Australian Museum responsible for the majority of specimen

identifications. The total of nineteen species (16 from the Abrolhos Islands and 7 from

Geraldton) were reported in this study, which is comparable to the study by Bennett

(2013). Bennett found 56 opisthobranchs in the Coral Bay region, 49 of these were

nudibranchs. Species came from ten different nudibranch families with seven of these

families also encountered in this study. Of the 49 species identified in Coral Bay, eight

species were also identified in this study, including the unidentified Gymnodoris citrina,

which was identified by Bennett as Gymnodoris sp. 1. The species Tritoniopsis alba was

identified in the study by Bennett (2013) at Coral Bay; expert consultation for this study

concluded that T. alba is only found in the northern hemisphere (pers. comm. Nerida

Wilson 2014). Therefore the species Tritoniopsis elegans is the correct species; with

distributions that reach the Indo-Pacific. This species was therefore counted as T. elegans

for comparisons with this study. There were 74 more species of opisthobranchs found at

the Dampier Archipelago than in this study of the Midwest region. All of the species found

in this study have a tropical, Indo-West Pacific distribution; none were temperate species.

It was anticipated that some temperate species would be found in this study as the

Abrolhos Islands is a transition zone for both tropical to temperate marine organisms

(Wells and Bryce, 1993). It might be expected that additional survey efforts in the Midwest

region will uncover a number of temperate species.

Comparisons of species abundance can be made with other studies in the Indo-Pacific,

outside Australia that had similar research methods. Chavanich et al. (2013) explored the

diversity and occurrence of nudibranchs in Thailand, finding Chromodorididae to be the

dominant family accounting for 35% of the total number of species found. This study also

41

found Chromodorididae to be the dominant family with 47% of the total number of species

(n=8). There were 96 nudibranch species identified in the study from Thailand, eight of

these species are the same as the species from this study. The remaining 11 species

from this study that were not found in Thailand were comprised mainly of chromodorids

that are endemic to Western Australia (Chromodoris westraliensis and Chromodoris cf.

westraliensis); and also species of chromodorids that require further genetic analysis,

destructive sampling for accurate identification and species that have only been identified

from the Ningaloo Reef (Chromodoris cf. annae, Chromodoris sp. 24 and Chromodoris cf.

sp. 24). Chavanich et al. (2013) concluded the study by stating “it is likely the present

number of Thai nudibranchs is an underestimation and that additional species will be

discovered in the future”. Future investigations will need to be made into the presence

and abundance of temperate nudibranch species at Geraldton and the Abrolhos Islands.

During the study, three sampling trips were carried out over a five month period, each in a

different season. The variation in numbers over each sampling trip is quite possibly

attributable to seasonality in nudibranchs, length of life cycle during each season and food

available in the habitat seasonally. Abundance fluctuations in nudibranch populations can

be explained by a reduction in food supply in a locality (Aboul-ela, 1959). Seasonality was

not a major aim of this study as time constraints did not allow a full year to collect a

complete data set; therefore the results presented from this study should be treated as a

‘snap-shot’ of species diversity and abundance in the Midwest region. The fieldwork

period was not long enough to determine any kind of seasonal trends; however small

scale seasonality may have played a role in the findings, with 20-30 less individuals found

during the winter survey trip compared to the autumn and spring months. Individual

nudibranchs were also observed to be notably smaller in size during the spring sampling

trip compared to the first two sampling trips (pers. obs.). If seasonality was to be

assessed, sampling would also need to take place in summer months and potentially for

two seasonal rotations to gain a better understanding of nudibranchs and their

42

relationship with the seasons. Some species of nudibranch live for several months while

others up to two years. Aerts (1994) found that temperature fluctuations over the seasons

have an influence on annual species of nudibranchs as they are not strongly associated

with their food sources. Sub-annual species are not directly influenced by temperature

fluctuations however. These species generally feed on seasonally variable resources

making the abundance of their dietary species the primary influence of population

abundance (Aerts, 1994; McCuller, 2012). Because the project used volunteer field

assistants, there is a possibility that some nudibranchs were missed while the volunteers

were developing nudibranch location skills. Using the same two divers for each of the

fieldwork trips would reduce this type of error.

4.2 Family Level Analysis

Species-level identification of nudibranchs from the genus Chromodoris was relatively

difficult. Due to this uncertainty, where possible, analysis of data was performed using

family or genus information. Colouration between species in the Chromodorididae is very

similar, making it hard to accurately differentiate between the different species. To

accurately identify nudibranch individuals to genus and species level without using

destructive sampling methods close attention must be paid to the visible distinguishing

features of each individual; these can be body shape, size, exposed or hidden gills,

whether pustules or cerata are present, and colour variation. Valdes et al. (2013) pointed

out the need for caution when making generalisations about the evolutionary role of

colouration in opisthobranchs; results from their study showed external colouration and

pattern of species not to be associated with genetic structure. The colouration of the

difficult individuals was all the same: blue, black, white and orange, with distinguishing

features being black line markings, presence of white along the edge on the mantle and

punctate pattern across the surface of the body. Consultation with taxonomic experts

concluded that if the individual had a punctate pattern with white pigment on the mantle

43

flap it belonged to Chromodoris annae but if it was found to have blue on the mantle flap it

belonged to Chromodoris westraliensis. If the animal had a dorsal black stripe between

the rhinophores but had clear markings from either C. annae or C. westraliensis it was

classified as similar to (cf.) these species. If there was no punctate pattern on the animal

at all it was then classified as Chromodoris sp. 24. (Rudman, 1984, 1998)

The most abundant family found was Chromodorididae. Chromodoris westraliensis was

the dominant species found during this study and is endemic to Western Australia (Wells

and Bryce, 1993), found in the Indo-West Pacific region, ranging from tropical to sub-

tropical zones along the Western Australian coast (Debelius and Kuiter, 2007). Rudman

(1991) found colour patterns in chromodorids can exist between unrelated species within

a colour group. These species can occur sympatrically in discrete geographic regions.

The colour groups for species are the most developed in isolated regions in warm

temperate or sub-tropical waters. Rudman found that species of sympatric colour groups

are often locally abundant with closely related species within a colour group, usually

allopatric with wide geographic ranges. Rudman also found that chromodorid nudibranchs

in semi-isolated geographic regions of high endemism, with high species diversity on the

fringes of main oceans, are considered the centers of chromodorid speciation; this

describes the exact location of the Abrolhos Islands. The Abrolhos Islands is an isolated,

remote area with several hundred kilometers to the nearest coral reef system. It is

believed that members of the Chromodoris genus are going through a phase of rapid

speciation at the moment along the Western Australian coastline (pers. comm. Nerida

Wilson, 2014). Assortive mating is one method that can lead to population subdivision,

adaptation and divergence (Faucci et al., 2007). Chromodoris produces planktotrophic

veliger larvae that undergo a short embryonic period before hatching after 5-7 days

(Trickey et al., 2013). Przeslawski et al. (2008) discusses groups of benthic invertebrates

that are potentially more vulnerable to extinction due to environmental change revealing

that gastropods with planktotrophic larvae development had the highest rates of

44

speciation. Further studies are being conducted by the Western Australian Museum,

awaiting genetic results to see if members of the Chromodoris genus are undergoing

acute speciation and creating hybrid species (pers. comm. Nerida Wilson, 2014).

High numbers of Chromodoris westraliensis individuals can indicate that this species is

thriving in its environment, being classed in less than 10% of species endemic to Western

Australia (Wells and Bryce, 1993). The second most abundant species found,

Chromodoris sp. 24 has not been fully described, although it has distinct markings and

has previously been found on the Ningaloo reef (Debelius and Kuiter, 2007). Johnson and

Gosliner (2012) researched the taxonomic evolutionary history of chromodorid

nudibranchs, revealing the need for more evolutionary studies of colour patterns and

trophic specialisation. They documented the many taxonomic, nomenclatural and species

delineation problems that still require refinement within the chromodorid nudibranchs.

4.3 Total Species and Abundance

Equal numbers of nudibranchs were found at shallow and deep sites. The depth

categories chosen (1-2 m and 5-8 m) support different organisms and consequently are

comprised of a number of different seaweeds and cnidarians that have been known to

influence nudibranch abundance (García-Matucheski and Muniain, 2011). Some species

of nudibranchs live at greater depths than others, with species found at depths ranging

from shallow reefs in Hawaii (Kay and Young, 1969) to abyssal shelves 4 km deep in the

Arctic (Jörger et al., 2014). A diversity survey in the United Kingdom focused on sites

ranging from 15 m to 40 m (Lock et al., 2010) resulting in the identification of 55 species.

There is limited published literature on depth variation in nudibranchs. Bennett (2013)

suggested that diversity increases with depth but may be related to increased water flow

in an area. The results of this study did not reflect a significant difference in the number of

species found at shallow or deep sites. Studies on depth categories of greater variation or

45

sites that are influenced by increased water flows may have returned a different result.

Habitat types and food sources for nudibranchs vary with depth, These factors are

presumed to be the main driver of abundance of species in an area. Investigations into

key nudibranch prey items; sponges, hydroids and bryozoans seasonal occurrence may

help in predicting abundance of sub-annual nudibranch species (Aerts, 1994; Lock et al.,

2010)

A significant difference in abundance of nudibranchs was observed between sampling

sub-regions. There was a clear difference between the number of individual nudibranchs

found at Geraldton, across both shallow and deep sites, and the three Abrolhos Island

groups. A significant difference of abundances was also observed between sampling sub-

regions at the Abrolhos Islands. There were clear differences in the number of species of

nudibranchs found at the Geraldton survey sites compared to the Abrolhos Island groups.

A significant difference was within the Abrolhos Island groups also observed when the

Geraldton sites were excluded from the analysis. These results indicate that Geraldton is

not the solitary driver for the initial significant result in both cases, although supporting

analysis of clustering techniques clearly identifies Geraldton as the main driver. Further

analysis showed a significant difference between island groups identifying the Easter

Group as having a marked difference in abundance and species numbers compared to

the two other island groups, indicating that Geraldton is significantly different to the three

island groups, with the Easter Group having a more subtle influence on abundance and

species numbers within the island sites. Further investigations into the abundance and

species of nudibranchs across the Abrolhos Island groups should be undertaken before

any conclusions can be made from these results.

The Easter Group had the greatest abundance and species of nudibranchs found in this

study. The Wallabi Group and the Pelsaert Group had similar abundance and numbers of

species with Geraldton having the least nudibranch abundance and number of species. A

steady decline in species abundance is present with increasing longitude, indicating

46

distance from the mainland may be linked to the influence of the Leeuwin Current. Garcia

and Bertsch (2009) found presence-absence of species in a biogeographical region to

have a latitudinal gradient in distribution when assessing genus level classification. The

overall abundance and distribution of nudibranchs across the study sub-regions were

significantly different, and perhaps related to the physical characteristics of the regions.

Domenech et al. (2002) observed that depth, water movement, habitat and presence of

prey in a location had an effect on the distribution of opisthobranchs. Higher energy

environments returned lower opisthobranchs in an area. The low number of nudibranch

species found at Geraldton may be attributed to the different marine environments in each

region. Geraldton does not receive the full influence of the Leeuwin Current like the

Abrolhos Islands, with the Capes Current influencing marine species when it is the

dominant current in summer months (Westera et al., 2009). The Abrolhos Islands and

Geraldton are home to a mixture of temperate and tropical species of marine flora and

fauna (Smale and Wernberg, 2012), although fewer tropical species occur in Geraldton

compared to the Abrolhos Islands. The coastline of Geraldton is a low to moderate energy

environment (characterised by stronger water movement from dominant swell). Strong

water movement causing sediment to re-suspend, creating turbid conditions in the area,

may have had an effect on nudibranch distribution and abundance. Habitat differences

and nudibranch prey items at each site contributed to nudibranch abundance in each sub-

region.

Anthropogenic effects on the Abrolhos Island reef habitats could potentially have an effect

in the abundances of nudibranchs found at each island group. The lobster industry at the

Abrolhos Islands has been established for generations and involves fishermen disturbing

the coral reef systems in localised areas with fishing equipment. The equipment is heavy

and has the potential to damage coral reefs, leaving areas of coral rubble, which

nudibranchs have been found to inhabit. Structural diversity of benthic ecosystems is

reduced by the used of mobile fishing equipment, that crushes, buries and exposes

47

marine animals (Watling and Norse, 1998). Further information on the effects fishing

activities have had on the Abrolhos Island benthic invertebrate marine environment needs

to be obtained. The degree of disturbance inflicted on the marine habitat over generations

should be investigated.

The influence of depth was analysed and showed no significance difference at the sites;

and there was no significant interaction found between depth and sub-region. Sub-region

was analysed alone and showed a significant difference, suggesting that the predominant

influence in nudibranch abundance and species richness is the region they are found in.

4.4 Species Diversity and Evenness

This study was carried out during the day-time, like the majority of species diversity

studies. Night-time surveys of nudibranchs have been relatively neglected posing the

question: do day-time surveys produce an accurate species diversity result? Nudibranchs

are cryptic, mysterious organisms with nocturnal tendencies (Gochfeld and Aeby, 1997).

Due to logistical constraints, night-time surveys were not conducted during this study,

implying predominantly nocturnal nudibranchs were not identified and were not included

in the abundance and diversity data presented in this study. Chang et al., (2013)

performed diel (i.e. day and night) surveys finding that different species were abundant

during the day-time compared to the night-time surveys. These results highlight the need

for an increase in diel or night-time surveys. Investigations into destructive day-time and

night-time surveys could also result in increased species diversity and abundance in an

area, as sections of reef nudibranchs are found inhabiting are rather complex. Without

destructively sampling these areas we will never gain a truly accurate species abundance

or diversity measure.

Although Geraldton had the lowest abundance of nudibranch out of the sub-regions, it

was quite diverse. Geraldton was found to have a greater species diversity than the

48

Abrolhos Islands; this is a rather surprising result. The Shannon-Weaver Diversity Index is

calculated using the proportion of species found relative to each other. There was a

greater unevenness in the proportions of species at the Abrolhos Islands, whereas

Geraldton had a more even proportion of each species. The intermediate disturbance

hypothesis states that local species diversity is maximised when ecological disturbance is

neither too rare nor too frequent (Rogers, 1993). The Geraldton marine environment is

more exposed to swell when compared with the marine environment at the Abrolhos

Islands and could be considered partially disturbed. Disturbance is defined as a

temporary change in average environmental conditions, causing a distinct change in the

ecosystem (Rykiel, 1985). Processes that effect benthic invertebrate populations found to

operate over small spatial scales (Olsen et al., 2014). Freshwater runoff in the coastal

waters of Geraldton from the nearby Greenough and Chapman Rivers are natural sources

of disturbance. Nutrients from agricultural catchment runoff can increase nutrients in the

surrounding marine environment when outflow is deposited (Devlin and Brodie, 2005).

River outflow events have created severe turbid conditions and sedimentation issues

along the coastline of Geraldton for several days (pers. obs.). Turbidity is considered a

disturbance factor, caused by natural or anthropogenic influences. Turbid conditions are

known to cause physiological stress on benthic invertebrates. The Leeuwin Current’s

effect on the biota in Geraldton may have more of an influence than research suggests.

All of the species of nudibranchs identified in Geraldton were tropical species. More

sample sites at Geraldton with more repetition would perhaps return a different result.

The Wallabi Group is more diverse in the deep sites compared to the shallow sites.

Commercial fishing activity or boating activity was found to decrease abundance of

nudibranchs in an area (Domenech et al. 2002). Relatively low densities of fishing

pressures exist at the Abrolhos Islands, with the benthic substrate unlikely to be

influenced by boating activity. The commercial fishery at the Abrolhos Islands is highly

unlikely to have an impact on the distribution and abundance of nudibranchs; hence the

49

more likely reasoning for this result is site selection. The shallow sites that were randomly

selected had less nudibranch species than the deeper sites.

4.5 Distribution

Geraldton was found to be distinctly different compared to the Abrolhos Island sites.

Differences in ecological and biological processes and habitat between Geraldton and the

Abrolhos Islands have been discussed in chapters above, with the dominant difference

likely due to the Leeuwin Current and its effects on the regions. Geraldton and the

Abrolhos Islands both had a tropical species composition, with no temperate species

found. The Wallabi Group is the northern most sub-region in the study. The high similarity

of clustering between the shallow and deep sites within this group could be due to benthic

habitat structure. The sampling design was random eliminating any bias when sites were

chosen. The Wallabi Group is situated further into the Leeuwin Current; found to be the

site of the most north-western sampling location in the study. The probable cause for the

difference in sub-regions is the influence the Leeuwin Current has on the habitat

composition.

The Leeuwin Current is believed to strongly influence recruitment of larvae with strong

recruitment linked to increases in invertebrate abundance in subsequent years (Caputi et

al., 1996). Watson and Harvey (2009) discussed fish larvae transport by the Leeuwin

Current from northern populations such as the Ningaloo Reef to southern ecosystems,

such as the Abrolhos Islands. Effects of larvae dispersal and recruitment by the Leeuwin

Current between the three Abrolhos Island groups were found to be substantially weaker;

although further studies are required to confirm this. The Leeuwin Current fluctuates

during the year, with its strongest influence being felt during the winter months. These

seasonal variations play an important role in the movement, survival and destination of

larvae along the Western Australian coastline (Caputi et al., 1996; Gaughan, 2007).

50

4.6 Substrate Preference and Activity

The literature has pointed to substrate preference of nudibranchs being highly dependent

on prey resources in the area. Chavanich et al. (2013) found the majority of nudibranchs

occured on coral rubble substrates (39%), followed by sand (28%) and sessile organisms

(25%). The preferred habitat for nudibranchs in this study was rocky reef and macroalgae

substrates closely followed by crustose coralline algae. This may be an indication of the

dominant flora present in the survey region. Rocky reef provides nudibranchs shelter and

is generally comprised of colonies of sponges, bryozoans and hydroids; ideal nudibranch

prey items. Bennett (2013) suggested that nudibranchs do not ‘live’ on the habitat their

prey items are found on, they feed and then move back to reside and shelter in rocky reef,

coral rubble or sand habitats. When located in-situ, 79% of nudibranchs observed in this

study were moving, predominantly across rocky reef, macroalgae and coralline algae

substrates. Stationary was the second most prevalent activity seen, with the majority of

stationary nudibranchs found on rocky reef, macroalgae and coralline algae as well as

sessile organisms. Results from this study show that the majority of nudibranchs found on

sessile organisms are stationary. Therefore it can be concluded that nudibranchs can be

seen ‘moving’ when in search for prey items and can be ‘stationary’ when feeding on said

prey item.

4.7 General Discussion

Climate change is already having impacts on marine environments around the world.

Species of mollusc have extended their range and now are spread further from the polar

regions than their natural distribution (Johnson et al., 2011; Perry et al., 2005). Prey items

of nudibranchs are also exposed to effects from climate change. Research involving

species of bryozoan communities in coral reef ecosystems has recorded local extinctions

51

in several species with an increase in sea temperature, suggesting that impacts on larval

survival and settlement are the most plausible explanation (Kelmo et al., 2004).

Nudibranchs are rather prey-specific organisms, only feeding on one or two species of

prey items (Faucci et al., 2007). In this case, if nudibranchs that feed on the bryozoan

species were present in the area they would also become extinct. Biodiversity variations,

population extinctions, habitat degradation and climate changes are all important issues

when monitoring biogeographical data (Bertsch, 2010). Nudibranchs are the top predator

in the communities they feed on and the presence of these gastropods can be an

indication of ecosystem health (Lock et al., 2010).

52

5.0 CONCLUSION

No quantitative information on nudibranchs is currently available for Geraldton or the

Abrolhos Islands; consequently this study focused on obtaining baseline data on species

abundance and diversity in the Midwest region of Western Australia. The species list

presented in Chapter 3 is the one of the first species list of nudibranchs to be created for

the Midwest region. Geraldton was found to be clearly different to the three Abrolhos

Island groups, with sub-region being a determining factor for abundance and species

abundance. The variable distribution of nudibranch species over the geographic range in

the Midwest is thought be due to the Leeuwin Current and the impacts associated with the

prey items and substrate types nudibranchs prefer. There are numerous biotic and abiotic

factors that influence the abundance of nudibranchs in a certain location; these include

swell, available food, turbidity, time of day, temperature or predator presence. The

Leeuwin Current is predicted to be the main influence on nudibranch distribution in the

Midwest, varying with seasonality. The prediction that nudibranch species abundance is

significantly different at varying depths was not supported by the findings of this study, but

investigations into the influence of the above biotic factors could highlight biogeographical

trends in nudibranch distribution. Further research into the degree of influence the

Leeuwin Current has on nudibranch populations in the Midwest region will allow future

predictions.

This study has added to our knowledge of nudibranchs in the Midwest region of Western

Australia. Subsequent studies in this region will produce a species list that will contribute

to the growing knowledge base of nudibranch diversity along the Western Australian

coastline and can help identify northern and southern limits of species distributions.

53

5.1. Future Implications

The Abrolhos Islands is a large and diverse marine environment that requires greater

sampling effort to gain a better idea of species and abundance of nudibranchs. Greater

sampling effort into destructive day-time and night-time sampling is also predicted to

increase the number of species and abundance of nudibranchs found in the Midwest

region.

To validate that high species diversity exists in Geraldton, additional, more intensive

biogeographical and quantitative studies are required in the sub-region. This should be

linked to research on the Leeuwin Current and the influence its processes have on

localised areas in an effort to determine if the current is the major influence on dispersal

method for nudibranchs that have planktotrophic larvae in the Midwest region.

54

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7.0 APPENDIX

Appendice 1:

A complete list of all 31 study sites, their GPS location, depth and site code name.

Table 1: Names and GPS coordinates of the sample sites at Geraldton and the Abrolhos Islands, including site code name, if the site is onshore or offshore and the average depth sampling was undertaken

Location Survey Site Site Code GPS Coordinates (S; E) Site Depth

(m)

Geraldton Port Gergory G11 28 11'2715" 114 14'2328" 2.0

Onshore North Marina 1 G12 28 45'1327" 114 36'5591" 2.5

North Marina 2 G13 28 45'1504" 114 36'5606" 1.5

Seperation Point G14 28 47'2361" 114 35'4389" 1.5

Drummonds G15 28 40'5683" 114 36'2220" 1.5

Lives 1 G51 28 46'371" 114 35'2186" 4.5

Lives 2 G52 28 46'080" 114 35'2211" 5.5

Wallabi Group W/Dick Island W11 28 29'6813" 113 45'2466" 1.5

Offshore S/W Gallows W12 28 28'8836" 113 45'9136" 1.5

W/Wann Island W13 28 28'0849" 113 45'2905" 2.5

Middle Ground W14 28 27'1022" 113 45'0080" 1.5

West Cardinal Marker W51 28 26'5860" 113 44'8144" 8.7

Public Mooring W52 28 27'7298" 113 46'1015" 6.8

Deep Lump Lagoon W53 28 29'0246" 113 45'3336" 6.8

Traitor Island W54 28 29'0299" 113 47'0203" 8.5

Easter Group Leo's E11 28 40'686" 113 52'435" 1.5

Offshore South Nature Strip E12 28 45'146" 113 45'629" 2.5

Middle Marker E13 28 43'1926" 113 47'5547" 1.5

Squid Hole E14 28 44'5509" 113 48'3843" 1.5

Kutas Corner E51 28 46'0388" 113 48'0899" 7.6

Three Sisters E52 28 44'4000" 113 44'0879" 4.1

Kacca Flat E53 28 45'2314" 113 45'2300" 7.1

Dougies Canyon E54 28 41'1950" 113 46'1570" 4.3

Pelsart Group Mid Rocks S11 28 53'9859" 113 55'3613" 2.4

Offshore South Basilie S12 28 53'3732" 113 57'4875" 2.0

Front Basilie S13 28 52'5158" 113 58'0028" 1.5

Public Mooring S14 28 51'419" 114 01'081" 1.5

66

Sponge Lump S51 28 53'1001" 113 58'3429" 7.7

East Gergory Island S52 28 53'7245" 114 00'7446" 7.5

Coral Patches S53 28 51'4992" 114 01'1586" 8.0

Coral Patches PM S54 28 51'2219" 114 00'6829" 5.7

67

Appendice 2:

Images of the dive site locations at each of the four regions

Figure 2.2: One of the four survey sites in the Geraldton region and the location of the five sampling sites (green balloons are shallow sample sites and green balloons with a dot are deep sample sites) (Google Earth, 2014).

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Figure 2.3: One of the four survey sites at Easter Group in the Abrolhos Islands region showing where the eight sampling sites are located (a pink balloon is a shallow sampling site and a pink balloon with a black dot is a deep sampling site) (Google Earth, 2014).

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Figure 2.4: One of the four survey sites at the Wallabi Group at the Abrolhos Islands region showing where the eight sampling sites are located (Google Earth, 2014).

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Figure 2.5: One of the four survey sites in the Pelsaert Group at the Abrolhos Islands region showing where the eight sampling sites are located (green balloons represent shallow study sites and green balloons with a black dot represent deep sampling sites) (Google Earth, 2014).