ASPECTS OF CORALLIVORY BY

CHAETODON UNIMACULATUS

IN KANE'OHE BAY, OIAHU

A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAII IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF SCIENCE

IN ZOOLOGY

By

Evelyn F. Cox

----------

Thesis Committee:

John S. Stimson, Chairman Stephen V. Ralston

S. Arthur Reed

We certify that we have read this thesis and that, in

our opinion, it is satisfactory in scope and quality as a

thesis for the degree of Master of Science in Zoology.

THESIS COMMITTEE

- . .. Chairman

\

ACKNOWLEDGEMENTS

To John Stimson, mahalo nui loa, for all his help

during this project. Many.thanks to Stev.e Ralston, Art

Reed, other member s of the f acul ty and staff of the

Department of Zoology, and my fellow graduate students.

Hawai'i Institute of Marine Biology furnished aquaria,

other supplies and the means of transportation to my

study sites in Kane'ohe Bay. And to Lester Zukeran, a

special thank you for supplying m~ with experimental

animals.

iii

ABSTRACT

Interactions between a corallivore, Chaetodon

unimaculatus, and the two dominant coral species in

Kane'ohe Bay, Montipora verrucosa and Porites ~pressa,

were investigated. Feeding selectivity was tested in

laboratory and field observations, with the fish clearly

selecting H. verrucosa: 39:1 bites in laboratory trials and

284:1 bites in field observations. Using an estimated

bite size of 2.54 mg AFDW and two estimated feeding rates,

4.88 bites min- l during the ndryn season (May to

September) and 7.20 bites min- l during the nwet" season

(October to April), an average sized fish consumes

approximately 4000 g of coral tissue each year, and the

population of ~. unimaculatus on Patch Reef #42 is

-removing approximately 10% of the standing crop of

~. verrucosa each yea~. A series of experiments was

designed to measure the effect of predation by these fish

on growth and ·competition between the two corals. Caged

colonies of ~. verrucosa at Patch Reef #42 had a vertical

growth rate of 9.71 x 10-3cmday-l, and M. verrucosa

killed ~. compressa tissue it came in contact with. In

tincagedc6T6iiles, . .M~ verruca-sa· gtew-ata rate of

3.92 x 10-3cm day-I, about 40% of the caged growth rate,

and several colonies showed a reversal of aggressive

dominance as predicted from previous studies, with

~. &Qmpressa killing branches of M. verrucosa. On Patch

Reefs #42 and #4~ there is a significant increase in the

iv

percent M. yerrucosa with increased distance from the edge

of the reef, where the fish are normally found, and grazing

pressure is greatest. Because of its selective feeding

behavior in Kane'ohe Bay, ~. unimaculatus appears to have

a significant effect on the growth and distribution of its

preferred poral species, B. verrucosa.

v

TABLE OF CONTENTS

ACKNOWLEDGEMENTS • . . . · . · . · . . · . . . ABSTRACT . . . . . . . · . . • eo.

LIST OF TABLES • • • • • • • • • • • • • • • • •

LIST OF FIGURES • • • • • • • • • • 8 • • • • • &

CHAPTER I. INTRODUCTION

Introduction • • The Study Site • The Corallivore

• • o • 8 • • • •

• • · . . . . . . . . • • · . . . . . . . .

CHAPTER II. FEEDING SELECTIVITY AND THE RATE OF CORAL CONSUMPTION

Introduction • · • .. • • • • • 0

Methods • • • • • .. .. • • • • .. • Results . • • • • • • • • .. • • • Discussion • • • • • • • • • • .. •

CHAPTER III. EFFECT OF PREDATION ON GROWTH AND COMPETITION BETWEEN MONTIPORA VERRUCOSA AND PORITES COMPRESSA

• • • •

• .. • •

iii

iv

vi

viii

1 5 8

11 13 19 24

Introduction • • • • • • • .. • • • •• 28 Methods .. • • • • • • • • • • • • •• 30 Results • • • • • • • .. • • .. • • •• 32 Discussion • • • • • • • • • • • • •• 38

CHAPTER IV. DISTRIBUTION OF FISH AND CORAL

CHAPTER V. --------------- ----- ------- ---- ---- ---

Introduction • Methods • • • Results ••• Discussion • •

· . . . . . . . . . . . · . . . . . . . . . . . · . . . . . . . . . . . · . . . . · . . . . CONCLUSION • • • • • • • • • • • · . .

REFERENCES CITED . . . • • • • · . · . · . . . .

vi

41 42 44 51

53

56

LIST OF TABLES

Table Page

1. Reported diets of ~. unimaculatus •••• • • 10

2. Results of laboratory feeding preference trials on ~. uniroaculatus • • • • • • • • • • • •• 20

3. Observations of field feeding preferences, Patch Reef #42. •••••••••••••• 21

4. Average bite size (mg AFDW) for laboratory held ~. unimaculatus •••••••••••• •• 22

5. Comparison of feeding rates of ~. unimaculatus at different times of year and day at Patch Reef #42. ••••••••••••••••• 23

6.

7.

8.

9.

10.

11.

12.

13.

Standing crop of ~. verrucosa on Patch Reef #42. • ••••••• • eo.

Comparison of morphological and skeletal properties of B. verrucosa and 2. compressa. •••••••••••••

• •

• •

Comparison of coral growth ratef in Kane'ohe Bay (change in radius in cm yr- ) ••••••

Series 1: comparison of vertical grow~h of B. yerrucosa and ~. coropressa on caged and uncaged screens on Patch Reef #42 (cm/160 days). ••••••••••••••

Series 2: comparison of vertical growth of H. yerrucosa and 2. coropressa on caged and uncaged blocks on Patch Reef #42 (cm/130 days), analysis by randomized blocks ANOVA with replication. •••••••••••••••

Series 3:" comparison of vertical growth of H. yerrucosa and ~. coropressa on caged and uncaged blocks at MokuoLo'e (cm/IOO days),

- - analysis--oy---ianaomized bTocKs--ANOVA with -- --replication. •••••••••••••••

Mean no. quanta (integrated over 10 seconds, 4 readings/block) for caged and uncaged treatments at MokuoLo'e (std.dev.) •••••

Comparison of growth rates (cm x 10-3 day-I) for both corals at the two study sites. ••

vi

23

25

29

33

34

37

38

40

14.

15.

16.

Comparison of coral cover and C. unimaculatus population size on selected patch reefs in Kane'ohe Bay. • ••••••••••••••

Percent cover of ~. yerrucosa with increasing distance from the edge of Patch Reefs #42 and 143. • ••••••••••••••••

Comparison of the time spent by C. unimaculatus in concentric zones on Patch Reef #42 (19 observation periods) =

vii

" ..

45

50

51

Figure

1.

2.

3.

4.

LIST OF FIGURES

Patch reef locations in Kane'ohe Bay. . . . Map of Patch Reef 142. • • • • • • • • • •

Total coral cover and number of ~. unimaculatus on selected patch reefs in Kane'ohe Bay. • ••••

Percent M. verrucosa and number of ~. unimaculatus on selected patch reefs in K~ne'ohe Bay. • ••••

viii

. . . . .

Page

6

16

46

48

CHAPTER I

INTRODUCTION

Two species of fish, of the genus Scarus, which are common here, exclusively feed on coral •••• Mr. Liesk assured us, that he had repeatedly seen whole shoals grazing wi th their strong bony jaws on the tops of the coral branches: I opened the intestines of several, and found them distended with yellow­ish calcareous sandy mud. (Darwin [1839] 1972:pp.402)

Small fish swarm about the branching clumps, and when disturbed, seek shelter at once among the branches, where they are safe from pursuit. The author has often witnessed this, and never saw reason to suppose they clustered about the coral for any other purpose. It is an undoubted fact, as stated by Mr. Darwin, that fragments of coral and sand may be found in the stomaches of these animals, but this is not sufficient evidence of their browsing on the coral. Fish so carefully avoid polyps of all kinds because of their power of stinging ••• that we should wait for further and direct evidence on this point. (Dana, 1872: pp.195)

The debate concerning the impact of coral reef

fishes on the growth, survival and competition of corals

'has continued since Darwin's time. Early anecdotal

reports of the impacts of fishes exist. Bertram (1936)

wrote that fishes in the Red Sea could affect the survival

of corals by scraping small amounts of surface area and

exposing the coral to algae and ?t~er boring organisms.

Motoda (1940) experimentally transplanted colonies of a

massive coral~ Goniastrea aspera, from the reef top at

Palau to the reef margin. Within one week, all colonies

suffered damage to the upper portions, presumably due to

fishes. A colony transplanted to mid-channel and

suspended from a float suffered no damage, presumably due

1

to the lack of grazing fishes venturing into deeper water

and off the bottom. He also reported that Porites

somaliensis on the reef margin often had white areas which

he attributed to fish damage.

By the 1960's, it was acknowledged by leading coral

researchers (Wells, 1957; Yonge, 1968; Stoddart, 1968)

that fishes could damage corals, but the impacts of fishes

were downplayed, with the emphasis being placed instead on

the importance of bioerosion due to invertebrates and

other boring organisms. Randall (1974) summarized

observations of fishes feeding on corals, listing members

of the families of Scaridae, Tetraodontidae, Diodontidae,

Balistidae, and Chaetodontidae as coral predators.

However, he writes,

It would seem that these fishes are not fully exploiting the coral resource as food. Part of the answer for some seems to be preference for other kinds of nutriment. Also there may be other reasons for the lack of abundance of these fishes than availability of food •••• Whatever the answer or answers may be, corals have been spared from excessive depredation by fishes. (Randall, 1974:pp.165)

Glynn and co-workers on the Pacific coast of Panama

have quantified the effects of predation on growth of one

species of coral, estimating that 1/3 to 1/2 of the annual

growth of Pocillopora ~icornis is lost to predation by

invertebrate and vertebrate corallivores (Glynn &

Macintrye, 1977). A study of the gut contents of 14

specimens of Arothron meleagris showed that a majority of

items in the guts consisted of coral fragments.

2

A. meleagris kept in experimental aquaria broke off pieces

of coral from colonies, ingesting about 44% of the pieces

broken off, and assimilating about 10% of ,the material

ingested (Glynn et al., 1972).

Neudecker (1979) transplanted colonies of Pocillopora

.da..micornis from the reef flat to the fore reef at Guam and

recorded skeletal weight losses of up to 25% within one

week. He observed balistids and chaetodontids feeding on

the test colonies. Caged colonies in all depth zones grew

equally well, leading Neudecker to hypothesize that fish

predation is the prime factor preventing ~. damicornis

from colonizing the fore reef zone.

Wellington (1982) studied the effects of a herbivorous

damselfish, Eupomacentrus acapulcoensis, on the

distributions of Payona gigantea and Pocillopora

damicornis on reefs off the Pacific coast of Panama.

Unlike chaetodontids which randomly graze on polyps or

balist~ds which can break off branches, this damselfish

nips away large contiguous patches from ~. gigantea,

apparently not as a source of food but to create

suitable bare patches for algal growth. The distribution

of ~. gigantea appears to be controlled by the actions of

the damselfish,' which limits this coral to deeper areas

where there is a lack of suitable shelter for the

damselfish. g. ~icornis is more resistant to damage, as

the damselfish can only remove the tips of branches. In

the deeper areas, however, g. damicornis colonies are

3

subjected to much higher predation pressure from other

corallivores.

Because of the ability of the coral to retract its

polyps into protective calices, the effects of

corallivores are probably similiar to those of herbivorous

browsers or grazers. Most corals are able to recover from

superficial damage, (see e.g., Bak et al., 1977; Bak &

Es, 1980), and colonies are unlikely to be killed by this

type of feeding behavior. However,' there may be secondary

effects of foraging on the coral's ability to compete with

other corals for space on well covered substrates.

Competition for space between corals, by differential

growth rates, overtopping or direct aggression, has been

postulated to be a major community structuring force in

dense coral stands in stable environments (Lang, 1973;

Connell, 1978; Richardson et al., 1979; Sheppard, 1979,

1982). If a corallivore preferred an aggressively,

dominant species, it could prevent monopolization of space

by the dominant species. If the corallivore were

selectively foraging on competitively inferior species, it

could contribute to the rarity of these species.

The purpose of this research was to investigate the

effects of a corallivore on the growth and distribution of

its coral prey, first by identifying any feeding biases

and quantifying the rate of cor"al removal, and then by

assessing the impact of grazing on coral growth, distribution

and the outcome of interspecific competition.

4

THE STUDY SITE

Kane'ohe Bay, located on the windward side of the

island of Olahu at 21 degrees 28 minutes North latitude

and 157 degrees 48 minutes West longitude, is the largest

sheltered body of water in the main Hawaiian Islandse The

bay is approximately 12.8 km in length and 4.3 km wide.

Depth of the lagoon area is generally 12 m. Water

temperatures range from 19.5 0 to 27.80 Centigrade,

with a mean of 21.60 C in January and 27.40 C in August

(Smith et al., 1973).

The north and central sectors of the bay contain a

number of patch ieefs, varying in size, shape, and depth at

low tide (Figure 1). Coral cover on patch reefs is

highest in the more northern areas of the bay, and Porites

compressa is the dominant coral species (Maragos, 1972).

Montipora yerrucosa is also common in the bay. At the

primary study site, Patch Reef 142, the top of the reef is

almost completely covered by large patches of ~. ~mpressa

and M. yerrucosa: both species displaying a blunt

finger-like growth form. Polacheck (1978) states that on

tliisf pat-chi"eeftnere lauric. -apparent patterri to the

relative abundance of ~. ~mpressa and M. verrucosa on the

upper surface" but that the slopes are dominated by

.£. cornpressa.

Fishes, and chaetodontids in particular, are abundant

on Patch Reef 142. Because of the simpliCity of the

5

Figure 1. -- Patch Reef locations in Kane'ohe Bay.

6

N

i PATCH REEFS iN

KANE'OHE BAY

,/ -", I I ! I I I \ , \ , , \ , \ , \

I \

43 ()04Z ,--.... _,: \

.0 0 \ "', .. _,'" " ~ ·'0 ' , o .. I '",,,,

300031 : "

~. ZTt) "',

026 " ' ...

, , , '"\

\ , I o 24 et2' o I •

23" ,\ ~ .. -- ... } \1 10''-........ : ' ....... ""

, ' -'I '0 / , (\ ,-~ • 1. ..... J ... _'

°0

00

o o~ a ~ "[J. .. 0 K U OL 0'£

•

composition of the coral community on this patch reef, the

high coral cover, and the abundance of chaetodontid

corallivores, Patch Reef #42 is an excellent site to study

the interactions between a corallivore and the coral

community.

THE CORALLIVORE

Previous studies of the family Chaetodontidae suggest

that some members of this family are important

corallivores. Gut content studies of seven chaetodontids in

the Marshall Islands indicated that s~x species fed, at

least in part, on corals (Hiatt & Strasburg, 1960). Of 13

species of chaetodontids found on the reefs of Kona,

Hawai'i, four species had coral tissue in their guts

(Hobson, 1974). Reese (1977) observed feeding behavior

and analysed stomach contents of 16 species of Chaetodon

in Hawaii and classified three species as obligate coral

feeders and three species as facultative coral feeders.

Birkeland and Neudecker (1981) compared two species of

Chaetodon found in the Caribbean. One species was

found to specialize on anthozoans, and its abundance was

. ___ .. __ EiJ gIJi fi<::CI. !1t.:J.Y_.9Qrl:'~1_~t; ~g._ w:itll.9Jv. ~l:'f3. :ity Ci1JCl._t. Q1:.Ci:J..':UIl.Q\l11 t. __

of coral cover.

Chaetodon IDulticinctus, ~. ornatissiIDYQ, and

~. trifasciatus were classified as obligate coral feeders

by Reese (1977). Of these, both ~. ornatissiIDYQ and

~. trifaciatus are common in Kane'ohe Bay. Of the three

8

facultative coral feeders, ~. Ynimaculatus,

~. guadrimaculatus, and~. reticulatus, only the first

occurs in K-ane'ohe Bay. ~. Ynimaculatus is the most

common coral feeding chaetodontid on patch reefs in the

north end of Kane'ohe Bay, ~. trifasciatus the next most

common, and~. ornatissim~ relatively rarer.

Reports of the diet of ~. Ynimaculatus include corals

and other invertebrates (Table 1). At Kona, Hawai'i, the

diet of ~. Ynimaculatus included 45% scleractinian corals,

"possibly fragments of. tissue and skeleton from

Pocillopora spp." (Hobson, 1974). Reese (1973) inspected

13 guts from ~. Ynimaculatus speared at Enewetak and found

primarily hard and soft corals, but also algal, sponge,

and polychaete fragments. Boucher (1977), studying the

behavior of this chaetodontid at Enewetak, found that

small individuals «8 cm total length) fed primarily upon

Montipora spp. (75% of the total bites tallied) while

larger individuals (>13 cm total length) took more bites

from soft corals (61% of the bi tes from Lobophyton spp.).

9

TABLE 1. -- Reported diets of ~. unimaculatus.

Area

Africa Africa

Australia

New Guinea Enewetak

Enewetak

Kona

Hanauma Bay

Diet

invertebrates soft corals, crustaceans soft and hard corals soft corals hard and soft corals hard and soft corals hard corals, invertebrates hard corals

Reference

Talbot, 1965 . van den Elst, 1981

Anderson et al., 1981

Tursch & Tursch, 1982 Reese, 1973

Boucher, 1977

Hobson, 1974

Motta, 1980

Motta (1980) attempted to correlate jaw structure in

five chaetodontids with their diets, and proposed that .

several features of ~. unimaculatus adapt it to feeding

upon hard corals: the robust mouth, stout"peripheral

teeth with high iron concentrations, and strongly braced

jaw. He observed feeding of ~. unimaculatus in Hanauma

Bay, O'ahu, and found it took significantly more bites

from Montipora spp. and Leptastrea spp., two uncommon

genera in tlie area, than from any other corals. Motta

suggested that the verrucosities on the surface of

H. verrucosa may supply leverage points allowing

m _~ ____ unJ_ml'£llJ!lEll_s_ ~()_~c:_r_al?~_~i_~~\lE! __ ~Ilcl _ ~~_e~_e_tCll ma 1:~_~~_aJ.

from the surface of the coral more effectively.

10

CHAPTER II. FEEDING SELECTIVITY AND THE RATE OF CORAL CONSUMPTION

INTRODUCTION

In order to assess the significance of corallivory on

the coral community, it is necessary to determine any

feeding selectivity for particular species of corals, the

rate of consumption of coral tissue and/or skeleton, the

standing crop of coral tissue available to feeding fishes,

and the replacement rate of coral tissue. Other effects,

such as a decrease in the competitive abilities of

preferred versus non-preferred corals, may also be

important.

There is a spectrum of ideas concerning the magnitude

of the impact of fishes on corals. There are those who

feel that predation by fishes on corals exerts a significant

impact on the annual growth and survival of corals and

thereby controls the distribution of coral species and the

composition of coral communities (Neudecker, 1979).

Alternately, there are those who believe that predation is

insignificant because of the colonial nature of the coral

animal and its protective. skeleton (Harmel in-Vivien &

Bouchon-Navarro, 1982). At this point, broad

generalizations about the impact of corallivory by fishes

on coral community composition cannot be made, in view of

the plethora of methods of feeding on coral and the

differential abilities of coral species to resist

predation.

11

Indirect measurements of coral consumption by

chaetodontids have been made by Harmelin-Vivien and

Bouchon-Navarro (1982). Based on gut weights and assuming

a twice daily filling of the gut, they concluded that

coral consumption by six species of Chaetodontidae amounted

to a maximum of 1 g m- 2 day-l (wet weight), from which

they concluded that chaetodontids browsing on coral polyps

do so without 'significantly damaging the corals. However,

they fail to provide data on feeding selectivity or coral

standing crop and replacement rates. Glynn and co-workers

(1979) used a similiar method to estimate removal of cor.al

by the sea urchin Eucidaris sp. They admitted that their

use of a 24 hour gut ftlling time was just an estimate,

but using this estimate, they calculated that ea9h individual

could remove 0.40 g day-l of coral. This rate of coral

removal was signficant enough to cause zero net production

by the. coral Pocillopora spp. in areas where coral cover

was less than 30% and consequently grazing pressure was

intense.

Feeding selectivity in- fishes has been studied in both

laboratory and field situations. Reese (1977)

investigated preferences in laboratory trials, by offering

two species of chaetodontids, ~. trifasciatus and

~. ornitissimus, simultaneous choice between three species

of corals, ~. verrucosa, ~. compressa, and 2. ~icornis.

Both chaetodontid species preferred 2. damicornis in these

trials. Birkeland and Neudecker (1981) compared bites

12

taken in the field by two chaetodontids, ~. capistratus

and ~. aculeatus, with abundances of different food

species in the feeding areas. ~. capistratus feeds on

scleractinians and showed some biases in food choice,

although they found that preferences in one location were

not consistant with preferences in other locations.

In order to assess any feeding bias by

~. Ynimaculatus, their feeding preferences in the

laboratory and field were measured. Consumption of coral

was estimated directly by evaluating bite size and feeding

rates, and an estimate of the proportion of the standing

crop removed by the fish was calculated using estimates of

coral removed per fish.

METHODS

LABORATORY FEEDING PREFERENCE TRIALS

Laboratory feeding preference studies were carried out

with five ~. unimaculatus captured from within Kane'ohe

Bay; two came from Patch Reef #42 and three came from the

Sampan Channel near the south end of the bay.

-Experimental anrma-rs-were placed TfidIvIdually inaquarTa

at the Hawai'i Institute of Marine Biology. Each aquarium

measured approximately 1.1 m x 0.6 m x 0.6 mi with a

volume of approximately 350 lof seawater. and a constant

inflow. Each aquarium had a clear window on one long side

permitting observations. Fish were given about 10 coral

13

heads of both species every other day for food. At least

48 hours were allowed for acclimation to aquaria before

trials began. Several small scarids or acanthurids were

added to each aquarium to control algal growth.

Before each trial all corals were removed from the

aquarium. Freshly collected test specimens of

.M. verrucosa and .f. compressa, both approximately 10 to

15 cm in diameter and having the same finger-like branching

form, were placed approximately 30 cm apart in the

aquarium. Left and right positions were alternated with

sequential trials. Data on the number of bites on each

coral species were recorded for 30 minutes, after a 10

minute adjustment period to allow the fish to habituate

to the presence of the observer at the window. Five or

six trials per fish were run on sequential days. Between

trials, fish were given additional corals for feeding. ,

FIELD OBSERVATIONS OF FEEDING PREFERENCES

After laboratory trials were completed, Fish #2, #3,

#4, and #5 were marked with anchor tags, injected

subdermally in the area beneath the dorsal fin. Tagged

fish were released on Patch Reef #42 in October of 1981. - --- -- -- - -- - -- ---- ----- ----------------- - -- -------- -------, - --------------------------- -- -

Fish #4 lost its tag within two days of release. Field

foraging information was collected from the remaining

three tagged fish while snorkeling near them as they fed

on the reef, counting the number of bites on each kind of

food during a 15 minute observation period. Coral cover

14

and the .size of the feeding area were estimated visually

while following the fish. Additional information on

interactions with other fishes was also gathered.

BITE SIZE

Ten fish were captured on Patch Reefs '42 and '43

and kept in flow-through seawater aquaria, approximately

390 1, at the Hawai'i Institute of Marine Biology. After

an acclimation period of at least 48 hours,. during which

H. yerrUCQsa was offered as a food source and replaced

every other day, all coral was removed from the aquarium.

Test colonies of B. yerrUCQsa, which had been stained with

Alizarin Red which colors the newly deposited skeleton

red, were placed in the aquarium. The number of bites

taken by the fish feeding on the test colonies was counted

. for a 30 minute trial period, and the fish was sacrificed.

Because~. unimaculatus takes skeletal material with each

bite (Motta, 1980), it was possible to dissect out the gut

and determine which portion contained the stained

material, usually the stomach and proximal segment of

intestine, approximately 28% of the total intestine - - - -- -- - - - - - -- - -- --------- ------- ------- - -

length. This section was squeezed to remove its contents,

which were then dried at 80 0 C for 24 hours, weighed, and

then ashed at 500 0 C for five hour's to determine the ash

free dry weight (AFDW). Because calcium carbonate will also

break down during the ashing procedure (Paine, 1971),

samples of pure calcium carbonate were ashed separately to

15

provide a correction factor for weight lost due to calcium

carbonate combustion in the gut samples.

FEED! NG RATES

Feeding rates were estimated during February and March

of 1983 by haphazardly selecting a fish in an area on Patch

Reef #42 (Areas A, B & C; Figure 2) and following it for

15 minutes, tallying all bites taken on coral. All fishes

were between 13 and 15 em in total length. The day was

arbitrarily divided into three time periods, morning (0700

to 1000), midday (1000 to 1400), and afternoon (1400 to

1700), to see if differences in feeding rates during

different periods of the day could be detected.

Feeding rates were again estimated during August of

1983, in the same area of Patch Reef" #42. To more

accurately sample periods when feeding rates might be

predicted to be elevated due to inactivity during the

night hours, feeding fish were observed at dawn

(starting approximately 15 minutes before sunrise and

continuing for about 1 hour), one hour around noon, and

dusk (starting approximately one hour prior to sunset and

"-ccnrtiifulfigUfitiT stirfsfetl. Hapnazardly-selecEedfish were

followed for five minute periods, tallying all bites on

coral.

16

Figure 2. Map of Patch Reef #42. A: Grid system, 20 m x 20 m, used to record

time spend in different zones on the reef (Chapter V)

B: Block placement in growth and competitionexperiment (Chapter III).

e: Area of contiguous H. verrucosa.

17

N-

~

PATCH REEF 42

STANDI·NG CROP

Dry weight of B. yerrucosa tissue cm-2 was estimated

at five si tes on Patch Reef 142 by collecting 10 cm x 10 cm

plugs. The plugs, consisting of skeleton and tissue,

were chiseled out to a depth of 10 cm; .below that depth

most coral tissue was dead, and exposed skeleton was

covered with other organisms. Samples were fixed in 10%

formaldehyde in seawater for 24 hours and then decalcified

with 4% nitric acid. The remaining material was dried for

24 hours at 80 0 C and weighed. There is a weight loss

(up to 10%) using this kind of technique (Davis, 1980).

RESULTS

LABORATORY FEEDING PREFERENCE

During the trial period, fish usually investigated

both specimens of coral, but fed almost exclusively on

H. yerrucosa. A simple G test of Goodness of Fit, using \

the extrinsic hypothesis that the number of bites on

~. compressa and H. yerrucosa should be equal, shows that

there is a significant preference for B. verrucosa, both

------ ----f-or--eacn-flsn-ana--poole-d--over-·-alr--inaIvi-dual-sT-ar~fi(Hign­

there are differences in the strengths of the response for

different individuals as evidenced by the heterogeneity

component (Table 2). This can be explained in part by

problems with individual fish and disturbances to the

trials; e.g., Fish #4 did not habituate to the presence of

19

the observer and sp~nt most of the trial periods in the

corner of the tank or swimming back and forth in front of

the glass window. Because of the outdoor location of the

aquaria, several of the trials were disturbed by events

such as coconut tree trimming.

TABLE 2. -- Results of laboratory feeding preference trials with ~. unimaculatus.

Fish no.

Bites - Bites -M.yerrucosa P.compressa

1 2 3 4 5

Test

3086 70 770 29

1011 33 35 0

352 0

. Pooled Heterogeneity Total

df 1 4 5

G 6226.7

26.2 6252.9

Total Bites

3156 799

1044 35

352

P<.OOI P<.OOI P<.OOI

G

3703.5 858.4

1154.4 48.6

488.0

To test if mechanical damage resulting from

transport; e.g., abrasion and mucus production, affected

choice of food, additional trials were conducted using

test corals which had been placed in the aquarium at least

24 hours in advance of the trial and were protected from the

fish by cylindrical wire cages. The results of these

tE!Cl~_E; __ appeared n()_dj.:f'~~rent froIll_~e original expE!rimE!lltal

setup. On several occasions, fish were observed to take

a bite of coral with a heavy mucus coat and spit out the

bite, suggesting that this species is not attracted to

excess mucus production by corals.

20

FIELD FEEDING PREFERENCES

Bites tallied during 17 observations periods of the

three tagged fish (Fish 12, 10 periods, Fish 13, two·

periods, Fish 15, five periods) also show a significant

deviation from a hypothesis of no preference for either of .

the two coral species (Table 3). H. verrucosa consisted

of less than 50% of the coral cover in the observation areas,

however it was preferred by a ratio of 284 bites

B. verrucosa to each bite on R. compressa.

TABLE 3. -- Observations of field feeding preferences, Patch Reef 142.

Bites - Bites - Total G M,verrucosa P,compressa Bites

2275 8 2283 3058· P<.OOl

Plankton feeding was sometimes observed, especially

duri.ng periods when dense patches of plankton were visible

in the water column, but it was difficult to quantify, and

even during periods of plankton feeding by all reef

fishes, ~. unimaculatus appeared to continue feeding on

hard coral, with occasional bouts of plankton feeding in

~. unimaculatus collected on Patch Reefs 142 and #43 also

reflect a preference for coral food: contents consisted

almost entirely of coral tissue, with a few algal

fragments and one small whole invertebrate.

21

BITE SIZE

BitE! size was determined for 10 fish, with a mean

of 2.54 mg AFDW bite-l (n=lO, s=1.78, Table 4). There is

some correlation between bite size and fish weight

(r=0.6519, 0.01<P<0.05), but because of the high variance,

it explains only approximately 42% of the variation in

bite size. Part of the variability is probably due to

some imprecision in segregating stained material from the

rest of the contents of the intestine.

TABLE 4. -- Average bite size (mg AFDW) for laboratory held 'c. unimaculatus.

Fish Weight Feeding Rate mg CaC03 Bite Size no. (g) (bi tes/min) per bite (mg AFDW)

1 52.6 9.4 0.3 0.5 2 69.1 3'.6 0.4 1.1 3 94.4 1.0 1.6 3.4 4 95.2 1.6 0.7 1.7 5 97.3 2.8 0.4 0.7 6 103.6 0.9 2.6 5.3 7 104.5 10.8 0.7 1.4 8 123.3 4.2 1.1 2.2 9 125.2 0.8 2.1 4.7

10 139.9 4.7 2.2 4.4

mean 2.54' std. dev. 1.78

FEEDING RATE

During February and March, there were no significant

differences among feeding rates during the three time

periods as determined with a 'Kruskal-Wallis Test (Table

5). Therefore" the data were pooled yielding an ~verage

feeding rate of 7.20 bites min- l (n=50, s=4.l5). During

22

August, a Kruskal-Wallis test again indicated no

significant differences among the three time periods

(Table 5), and the data were pooled for an average rate of

4.88 bites min-l (n=129, s=5.32). There does appear to be

a difference between the "winter" and "summer" feeding

rates, however, they are not comparable statistically due

to the different observation techniques and different

times of the day selected.

TABLE 5. -- Comparison of feeding rates of ~. unimaculatus at different times of year and day at Patch Reef #42.

February/March

min- l Morning Midday Afternoon Pooled

Ave bites 7.96 5.49 7.65 7.20 Std. dev. 2.40 3.77 5.53 4.15 Range 2.5-11.8 0-12.1 0-24.9 No. fish 19 13 18 50

August

min-l Dawn Noon Dusk Pooled

Ave bites 5.51 5.88 3.81 4.88 Std. dev. 4.78 7.03 4.58 5.32 Range 0-21.4 0-27.2 0-14.8 No. of fish 44 39 46 129

STANDING CROP

Five samples of .M. ~.r..w:;,.Q§.a from within 4 m of the

edge of Patch Reef #42 were analysed, resulting in an

estimate of 660 g (tissue dry weight) m- 2 (Table 6). ----------------- --------------- --Bowev-er;---oeca-u-se--ortli-eIr-sTze-an-a--feecUng- behavior,

~. unimaculatus are not able to utilize all of this

tissue. These fishes can only remove the top layer of

tissue and skeleton, probably less than 10% of the

standing crop as estimated using this method.

23

TABLE 6. -- Standing crop of ~. verrucosa on Patch Reef #42.

Sample no.

mean

1 2 3 4 5

std. dev.

dry wt (g)

7.117 6.066 7.570 4.454 6.787

6.599 0.843

DISCUSSION

~. unimaculatus in northern Kane'ohe Bay is clearly

selecting one species of coral, H. verrucosa. Feeding

preferences for two other HawaiIan chaetodontids,

~. ornatissimus and ~. trifasciatus, have been studied by

Reese (1977), by offering captive pairs of chaetodontids a

simultaneous choice of three species of corals. For both

chaetodontids, Pocillopora damicornis was the preferred

'coral, fOllowed by .M. yerrucosa, with of. compressa third.

However, the prefere~ce for .M. yerrucosa over of. compressa

does not seem as strong as I recorded while comparing only

two species. The mean number of bites/50 min observation'

period (n=82 trials) by ~. trifasciatus on of • .aa,m'icornis - ---- -- -- - - - - ----- --

was 112.6, for }1. yerrucosa 80.6, and for of. compressa

55.2, indicating only a weak preference for H. verrucosa

over of. ~mpressa. In the northern end of Kane'oheBay,

~. damicornis is a less abundant and patchily distributed

component of the fauna, representing less than 1% of the

coral cover on Patch Reef #42. ~. trifasciatus feeds on

24

both ~. compressa and H. verrucosa at Patch Reef #42

(personal observations).

Hobson (1974) suggests that Pgcillopora spp. are the

most common food of ~. unimaculatus based on coral tissue

in the gut, but this may reflect the relative abundances

of corals on the leeward coast of the island of Hawaili.

Pgcillopora spp. are more common than Mgntipgra spp., with

~. meandrina representing approximately 16% of the total

coral cover, H. yerrucgsa less than 2% (Dollar, 1980).

Pteferences by large~. unimaculatus for soft corals

as shown by Boucher (1977) at Enewetak and feeding on soft

corals as reported by Anderson et ale (1981) and Tursch &

Tursch (1982) cannot be observed in Kanelohe Bay, as soft

corals are not present. There is a location off the coast

of Molokali where large beds of soft corals and

~. unimaculatus co-occur (J. Maragos, personal

communication), and this may be an ideal site to

investigate preferences for soft corals in Hawaili.

H. verrucosa may be the preferred 90ral for anyone

or a combination of factors. It has a deeper penetration

of tissue into the skeleton and lower skeletal density

- _uum -tnan-.f~-cQmpieSSfc"--{T-aDI e --6r1-factor sU·W-hIC1i -Iliay--allow -

~. un:i;maculatus to remove more tissue per bite. However,

H. verrucosa may have a higher resistance to abrasion than

1:. compressa. Other possibilities included differential

caloric content, nematocyst size and denSity, and/or the

presence of toxic compounds.

25

TABLE 6. -- Comparison of morphological and skeletal properties of ~. verrucosa and R. compressa.

l?roperty

Depth of tissue

Density Displacement

X-ray

% loss in abrasion test

!1.yerrucosa

13.0 mm

0.92 glcc 1.37 g/cc 1.10 g/cc

38.8%

R.compressa

7.5 mm

1.18 g/cc 1.41 g/cc 1.23 g/cc

47.4%

Reference

Polacheck, 1978

White, 1980 Maragos, 1972 Houck, 1979

Jokiel & Cowdin, 1976

The importance of feeding preferences in understanding

the consumer's impact on producer populations has been

underscored by experimental analyses of the effects of

herbivores on marine algal populations (for a review, see

Lubchenco & Gaines, 1981). The.effect of the consumer on

plant diversity depends largely on the selectivity of

grazing and on the competitive abilities of the plant

species. Selective grazing can have opposite impacts on

divers"ity; for example, the effect of the snail Littorina

littorea on algal diversity depends on environmental

conditions: its preferred food· species is competitively

dominant in tide pools but is inferior to other algal

__ ~.E~~Je.§l_ ~n_ ~!llE!~9.~_n! __ ~~~~_t_r_Cl_t:~ __ tr,.~!>!=jl_encQL_19I~1~ ___ '!'lt~ ________________ _

impact of selectivity by~. unimaculatus on growth and

competitive abilities of the two corals was studied in

another series of experiments (Chapter III).

Reproduction by ~. unimaculatus probably occurs

during the months of February, March, and April (Lobel,

1977; personal observations). Increased energetic needs

26

during the reproductive period may be a factor in the

higher feeding rates recorded during the February/March

period, although the pooled means are not directly

comparable due to the different sampling periods used and

the difference in division of the day into sampling

periods.

The magnitude of the consumption of coral by

~. unimaculatus can be estimated by using the feeding

rates as indicators of feeding during the two periods of

the Hawaiian yearly cycle, the dry period or kau (May to

September) with day lengths of approximately 13 hours, and

the wet period or hotoilo (October to April) with day

lengths of approximately 11 hours. Using mean feeding

rates for these two periods and the mean bite size, .a fish

could remove approximately 4000 g per year, or the

population of approximately 168 fishes (with a mean size

equivalent to the average sized fish used in laboratory

bite size calculations) on Patch Reef #42 is removing

670,000 g per year from the reef. Using estimates of the

total amount of H. verrucosa on Patch Reef #42 (see

Chapter IV) and the standing _crop_of c()I'~l 1;i_flsuep~r

square meter, this fish population is removing about 10%

of the standing crop each year.

27

CHAPTER III. THE EFFECT OF PREDATION ON GROWTH AND COMPETITION BETWEEN M. VERRUCOSA AND ~. COMPRESSA

INTRODUCTION

Competition for space between corals, by differential

growth rates, overtopping or direct aggression, has been

postulated·to be a major community structuring force in

dense coral stands in stable environments (Lang, 1973;

Connell, 1978; Richardson et al., 1979; Sheppard, 1979,

1982). However, the outcomes of competitive interactions

may be modified by other factors including the delayed

development of sweeper tentacles (Wellington, 1980), the

site of the interaction (Bak et ale, 1982), or activities

of the epifauna present (Bak et al., 1982).

Corallivores have been found to depress growth rates

of corals (Glynn et al., 1972; Neudecker, 1979), and may

also affect outcomes of competition for space. The impact

of a selective corallivore on the growth and competitive

interactions of corals depends on which coral is the

preferred food species for the corallivore. Following

results based on work with marine herbivore preferences

ClI'l9 __ ~1_g~1 divers.i.i:.y_LfoI' a review,SeELLubchenco .. ~. Gaines,

1981), if the corallivore preferred the aggressively

dominant species, it may prevent monopolization by the

dominant ~pecies in dense coral stands. Selectivity for

subordinate species could make those species extremely

rare.

In Kane'ohe Bay, both ~. verrucosa and ~. compressa

28

have similiar growth rates, in studies of isolated colonies

(Table 8), and colony morphologies. In experimental

tissue transplantation reactions, H. verrucosa displays a

unilateral xenogeneic incompatibility against R. compressa

(Hildemann et al., 1974); i.e., .M. verrucosa was able to

kill tissues of R. compressait came in contact with,

similiar to aggressive encounters of the type described by

Lan g (1 97 3) •

TABLE 8. -- Comparison of prowth rates in Kane'ohe Bay (change in colony radius in cm yr- )

.M. verrucosa

1.85 1.31

.f. compressa

2.43 1.28

Reference

Polacheck, 1978 Maragos, 1972

Other researchers have noted that H. verrucosa has the

ability to grow up and over R. compressa (Branham et al.,

19711 Maragos, 1972; Dollar, 1975). Polacheck (1978)

characterized 51 naturally occuring interfaces between

.M. yerrucosa and R. compressa on Patch Reef 142. He

classified H. yerrucosa as the dominant coral in 14% of

the interactions, a standoff in 84% of the interactions,

and subdominant to R. compressa in 2% of the interactions.

The high proportrons ofu standoffs between l:1.Yerrucosa and

R. ~mpress.a on Patch Reef 142 may resul t from the impact

of a selective corallivore, ~. unimaculatus. The effects

of predation on the outcome of interactions between two

species, with a dominance ranking as determined by

laboratory experimentation and field observations, can be

29

tested because the predator, in this case, is clearly

selective in its feeding preferences.

METHODS

To test for differential growth and competitive

interactions with and without predation, pairs of

~. verruocsa and ~. compressa were collected from MokuoLo'e

reef and artificially placed in contact inside and outside

of predator exclusion cages. To insure genetically

matched protected and unprotected pairs of the two coral

species, coral colonies of each species were cut in half

with a rock saw, which was cooled with salt water during

cutting to minimize tissue damage. Corals normally heal

along such cut surfaces. For the first experimental

series of 12 pairs, the two corals were tied together, cut

sides in contact, with monofilament line, and then each

set of competitors was wired to a screen, in its original

vertical orientation. One pair of each of the matched

sets was protected from chaetodontid grazing by chicken

wire cages, the other pair was left unprotected. Corals

were stained with Alizarin Red to permit measurement of

Tineai-growth, from-t:he--stained sKeleton to the outer edge

of the corallum. These screens were placed at the edge of

the top of Patch Reef *42 on January 12, 1983, at

approximately 2 m depth. Cages were brushed every week to

prevent algal buildup. The screens were removed from the

field after 160 days. In some cases the monofilament line

30

did not hold the two corals together and was replaced with

plastic coated wire. Two halves of ~. verrucosa .were lost

during the trial period, and one set of pairs was removed

from the data analysis because the corals became

separated. For each set, percentage of the colony surface

which had die.d was est1mated, and vertical growth was

calculated by cutting a minimum of ten branches and

measuring skeletal growth in the axial plane beyond the

Al iz ar in Red stain.

A second series of experimental pairs was prepared by

glueing the cut corals to concrete blocks with Sea Goin'

Putty, with cut surfaces flush to the block face and

branch tips in contact. Again, one set of competitors was

prot.ected from chaetodontid grazing by chicken wire cages,

and the other set was left unprotected. This series of

twelve paired blocks was placed in a similiar position on

Patch Reef 142 on March 29, 1983, and removed after 130

days. Cages were brushed at least once per week to

prevent algal buildup. Colony mortality was estimated and

vertical growth was measured b¥ cutting a sample of ten

branches. Observations of direct killing of opposing

---------- -crancfie s -ana -o-vergrowtli--w-ere--aTso--macfe:-· - ------- ------------------------ - - - - --------- --- - -------- -----

Another chaetodontid, ~. trifasciatus, feeds on •

~. verrucosa in laboratory situations (Reese, 1977).

~. trifasciatus occurs in low densities on Patch Reef #42.

In an attempt to separate out the effects of this

chaetodontid on competition between corals from that of

31

~. unimaculatus, the third series of five experimental

sets, prepared identically to the second series, was

placed at approximately 2 m depth off the fringing reef at

MokuoLo'e, an area lacking in ~. unimaculatus, but with a

similiar density of ~. trifasciatus as Patch Reef '42.

Thi s ser ies was put out on June 17, 1983 and removed af ter

100 days. Colony mortality and growth were measured as

previously described. Light levels inside and outside of

cages were measured with a Li-Cor Integrating Quantum,

Radiometer and an underwater quantum sensor'.

RESULTS

SERIES 1

Several of the sets did not survive the experimental

period, either coming apart from each other or coming

loose from the scr,een. Damage from contact of cut

surfaces with other corals seemed to affect both species,

although B. verrucosa consistently had a wider margin of

dead tissue at the interface. On the basis of at-test

for paired comparisons, there was no difference in growth

rates for ~. compressa in the two treatments (t=0.5l2, - ---- -- ------- - -- -- ---- -------

- - -d~=I6; -,TacIe--9r;- but caged B. verrucosa grew significantly

taller than uncaged colonies (t=4.657, df=1'6, Table 9).

32

TABLE 9. -- Series 1: compar~son of vertical growth of ~. verrucosa and ~. compressa on caged and uncaged screens on Patch Reef #42, (cm/160 days).

Pair no.

~. verrucosa caged uncaged

2 0.92 3 0.47 5 0.99 6 1.03 8 1.11 9 1.50

10 1.54 11 0.94 12 1.17

mean 1.07 std.dev. 0.32

SERIES 2

o o

0.30 0.52 0.53 0.40 0.45 o

0.48

0.30 0.23

~. compressa caged uncaged

0.99 1.16 0.86 0.80 0.89 1.11 1.00 1.18

" 1.02

1.00 0.13

0.92 0.98 1.12 1.11 0.94 0.91 1.14 1.08 1.06

1.03 0.09

There appeared to be less mortality following the

cutting procedure than in series 11 in fact most of the

colonies we~e growing over the putty and out onto the

block surface at the end of the experiment. Thr·ee sets of

corals were eliminated from the analysis: H. verrucosa on

the uncaged block of pair #2 came unglue"d and was lost,

corals in pair #11 became partially unglued, and pair #12

was overturned during a period of heavy surge and was

. cl~s_t_r9Y~cl._ J~~I'_tl<:~l_gI'~wt;h_()f~CJ.c::Jl_f3P_ec:iel:iw_a.sanalys_ed ______ _

as a randomized blocks ANOVA, with replication from 10

branches per coral. ~. compressa shows no significant

difference between caged and uncaged treatments, however,

there are some differences among individuals (Table 10).

The analysis of the data for ~. verrucosa indicated a

significant interaction component, i.e. all pairs were not

33

TABLE 10. -- Series 2: vertical growth of M. yerrucosa and ~. ~mpressa on caged and uncaged blocks on Patch Reef #42 (cm/130 days), analysis as randomized blocks ANOVA with replication.

~. compressa

Pair No. Caged Uncaged 1 1.13 1.06 3 0.76 0.98

" 0.96 0.99 5 1.05 1.02 6 1.02 1.00 7 1.05 0.99 8 1.08 0.98 9 1.14 1.06

10 0.96 0.99 .

mean 1.02 1.01 std.dev. 0.12 0.03

ANOVA Source of variation df MS F Treatment 1 0.02405 1.109 n.s. ·Individua1s 10 0.10248 4.726 P<.OOl Interaction 10 0.04524 2.087 .025<P<.0 5 Error 198 0.02168

·B. yerrucosa

Pair No. caged uncaged 1 1.36 0.54 3 1.11 0.09 4 1.28 0.82 5 1.18 0.67 6 0.93 0.91 7 1.74 0.97 8 1.21 0 9 1.21 0.54

10 1.43 0.84

mean 1.27 0.60 - ---- ------ --- -- -- -- ------------

std. dev •. 0.23 0.35

ANOVA Source of variation df MS F Treatment 1 19.39057 475.6 Individuals 7 1.36156 33.4 Interaction 7 0.47313 11.6 P<.OOl Error 144 0.04077

34

responding in a consistent manner. Part of this may be

related to the substrate on which the blocks were placed

(Area B of Figure 2). Sets #5, #6, and ilO were placed.on

the tongue of B. yerrucosa which approaches the edge of

the reef. The two sets with the poorest growth rates, #8

and #3, were at the other end of Area B, placed on

~. compressa. The data were also analysed as a paired

t-test comparing mean growth in uncaged and caged pairs.

Growth of B. yerrucosa was significantly greater in caged

cor al s (t = 4.867, d f = 16, P < • 0 01) •

Where branches of the two competitors came in contact

there was a zone of dead tissue, usually on both species,

with algae covering the exposed corallum. Where branches

did not come in contact, no dead zones occured. Using

predictions of aggressive dominance of ~. yerrucosa based

on immunological work, in which ~. yerrucosa consistantly

killed ~. coropressa tissue that was in contact with it,

there should have been more dead surface on 2. ~pressa

than on M. yerrucosa. However, on the uncaged pairs i8,

#3, and #10, 2. ~mpressa had caused significant mortality

to B. yerrucosa; some branches of B. yerrucosa were dead

tiff to- l~cm. --In contrast, in caged situatiori-s, theEe were

two cases, pairs #8 and #9, where a branch of M. verrucosa

was enveloping the opposing branch of ~. compressa. Ih

the other caged pairs, M. yerrucosa had killed the tissue

of P. ~mpressa, in some cases as much as 1.5 cm of the

contacted branch.

35

SERIES 3

There are no significant differences between treatments

or among individuals for ~. compressa. B. yerrucosa shows

significant effects both between caged and uncaged pairs

anq among individuals, with higher vertical growth in the

caged treatment (Table 11).

36

TABLE 11. -- Series 3: comparison of vertical growth of M. yerrucosa and ~. ~mpressa on caged and uncaged blocks at MokuoLo'e (cm/100 days), analysis by randomized blocks ANOVA with replication.

~. coropressa

Pair No. caged uncaged 1 0.95 0.86 2 0.91 0.88 3 0.94 0.94 4 0.97 0.99 5 0.96 0.96

mean 0.95 0.93 std.dev. 0.02 0.05

Source of variation df MS F Treatments 1 0.01000 0.076 n.s. Individuals 4 0.02585 0.197 n.s. Interaction 4 0.00925 0.070 n.s. Error 90 0.13141

11 •. yerrucosa

Pair no. caged uncaged 1 0.88 0.62 2 1.18 0 .. 65 3 1.37 0.88 4 1.29 0.86 5 1.26 ·0.90

mean 1.20 0.78 std.dev. 0.19 0.14

Source of variation df MS F Treatments 1 4.28490 134.57 P<.OOl Individuals 4 0.48385 15.19 P<.OOl Interaction 4 0.05765 1.81 n.s. Error 90 0.00318

- - - -- - --

37

LIGHT LEVELS

Caging resulted in a decrease of approximately 24% in

Photosynthetically Active Radiation (measured in quanta)

(Table 12) .•

TABLE 12. -- Mean number quanta (integrated over 10 seconds, 4 readings/block) for caged and uncaged treatments at MokuoLo'e (std.dev.).

Pair no.

1 3 5

caged

393 (8.0) 444 (6. 2) 490 (6.5)

DISCUSSION

uncaged

493 ( 8.7) 583 (15.6) 758 (10.1)

'i,.".,. 1\ nU.,er of factors could produce a difference in the

vertical growth rates of ~.yerrucosa inside and out~ide

of predator exclusion cages on Patch Reef #42, including

various cage artifacts and the exclusion of other

corallivores. .It is clear th~t exposure to grazing by

fishes has a detrimental effect on the growth of

~. yerrucosa. The appearence of the surface of the

severely grazed test colonies of ~. yerrucosa from· Patch

Reef #42 resembles the gnawed appearance of colonies left

for several days in aquaria containing ~. un,imaculatus.

~. trifasciatus has a less well developed jaw and tooth

structure (Motta, 1980), which it uses to delicately

remove coral polyps, and presumably its ~ore delicate

mouth is less able to remove skeletal material than

~. YDimaculatus. Other researchers (Motta, 1980;

T. Hourigan, personal communication) indicate that

38

~. trifasciatus takes single polyps or parts of polyps

with each bite, a type of feeding behavior which would not

produce severely gnawed surfaces.

There were distinct changes in the growth morphologies

of H. verrucosa in the two treatments. Uncaged specimens

had thicker, stubbier branches, while the caged colonies

had thinner, finer branches. This undoubtedly affects the

measurement of growth, as thinner branches may show more

vertical growth, but lateral expansion of the stubbier

branches may represent as much mass change as the thinner

branches.

The reduction of light levels within cages may have

an effect on coral growth rates. Studies have shown that

H. verrucosa grows faster in reduced light levels (Houck

et al., 1977; Coles & Jokiel, 1978). However, these

studies indicate a plateau in the increased growth rate

after a reduction to 70 to 50% of the surface incident

solar radiation. 'Typical calculations of natural

attenuation of light with depth suggest that by 2 m depth,

light levels have been reduced to 50% of surface incident

solar radiation (Coles & Jokiel, 1978). Therefore, it

seems unlikely that the additional de'crease in light

levels within the cages would significantly alter growth

rates.

The effects of the cages on water motion are more

difficult to assess. Even if the cages do not appreciably

decrease the total volume of water passing by the corals,

39

they could alter the pattern of flow, perhaps allowing the

coral to construct thinner branches.

There is a between site difference in growth rates

for both coral species (Table 13). Part of this

difference may be due to the additional month of growth of

the corals at MokuoLo'e under elevated summer temperatures,

as temperature has been shown to increase growth rates

(Maragos, 1972; Coles & Jokiel~ 1978). Other physical

parameters may differ between the two sites. However, it

is readily'apparent from these data that the between site

differences'represent an approximate 18% decrease in

growth rates at Patch"Reef #42 for all treatments

excepting the uncaged !1. verrucosa. ,In the presense of

abundant ~. unimaculatus, the selective corallivore,

!1. verrucosa suffered an additional decrease in growth

rate of approximately 32%, presumably due to the effects of

grazing by ~. unimaculatus.

TABLE 13. -- Comparison of growth rates (cm x 10-3 day-I) for both corals at the two study sites.

Site

Patch Reef -#42

MokuoLo'e

!1.yerrucosa uncaged caged

3. 9~- 9-.71

7.82 11.96

40

.f.compressa uncaged caged

1.74·

9~26

7.82 -

9.46

CHAPTER IV. DISTRIBUTION OF FISH ANP CORAL

INTRODUCTION

Specialized foragers are found in areas in which

their preferred food resource occurs, for example the

distribution of the coral feeding gastropod Coralliophila

abbreyiata is positively correlated with the percent of

the coral genus Montastrea (Ott & Lewis, 1972). In

Kane'ohe Bay, ~. unimaculatus is highly selective for the

coral B. yerrucosa, and therefore its distribution would

be predicted to be strongly correlated not with the total

amount of coral cover on a patch reef but with the percent

of B. yerrucosa available to the fishes.

Consumers are often restricted in their foraging area

by a need to remqin close to shelter from predation: the

presence of "haloes" in the distribution of seagrasses around

patch reefs in the Caribbean is generally attributed ~o

the need of herbivorous fishes and urchins to have shelter

from predators (Randall, 1965; Ogden, 1976). Menge and

Lubchenco (1981) suggest that high predation pressure

on marine herbivores in tropical environments creates

-stl'Qnq -9-~aQien-ts-i-n-'-ca-nsumer---EJ-r-az-in(J-pl"-es-su-r-e-on-'a-lEJae.----

If ~. unimaculatus is similiarly limited in its grazing,

needing to remain close to the slope for access to shel ter

in the large blocks of 2. compressa, and~. unimaculatus

has an effect on the growth of B. verrucosa (and its

ability to compete for space with ~. ~mpressa), then the

41

percent of M. verrucosa should increase with increased

distance from the slope.

METHODS

A subset of patch reefs in the north and central

sectors of Kane'ohe Bay were selected for the estimation

of coral cover and~. unimaculatus density. The reefs

were chosen to give a range of total coral cover from low

to high, estimated by visual surveys, and on the basis of

size and simplicity of shape. Reefs differed in depths at

low tide, with some partially exposed at extreme low

tides, whil"e others were always covered with at least 1 m

of water. Because of the unknown extent of utilization of

the reef top, total coral cover and the percent coverage

of the major species were measured along the edge of the

reef top, with meter square quadrats placed just below the

break between the top and slope. The enti're circumference

of each reef was sampled, advancing by a random number of

kicks between quadrats. Preliminary plots of both the

culmulative percent total cover and percent M. verrucosa

against the number of quadrats were used to evaluate the

adequacy of -thesample--size.-

Fish populations were censused from May 1982 through

August 1983, when water visibility permitted. A number of

fish censusing techniques have been developed (for ~

review, see Sale, 1980). Because~. Ynimaculatus

typically swims off the reef top to the slope when

42

disturbed, all ~. unimaculatus seen at the edge or on the

slope to the bottom of the reef were counted when passed

while slowly snorkeling around the perimeter of the reef.

This method was judged to give a reasonable estimate of

the population size, although comparatively low counts on

days of extremely good visibility suggest that fish may

be able to observe the census taker, go into cove~ and

thus are not counted.

The perimeter of each reef was determined using the

formula for the ·circumference of an ellipse, the basic

shape of these reefs, and data on reef size from Roy

(1970). To compare between reefs of differing sizes,

fish populations were expressed as the number of

~. unimaculatus per meter of reef ~erimeter.

Patch reefs 142 and 143 were selected to evaluate

the distribution of B. yerrucosa along concentric

transects in toward the center of the reefs. Both reefs

support large populations of ~. unima¢ulatus. Percent

M. yerrucosa was measured with meter square quadrats at

four distances from the edge. Placement of the quadrats

was accomplished by swimming a random number of kicks at

______________ the __ edq el--- __ dr opping. __ an __ anchor-ed-to-p-e,-and-aw-i-mmin9--the------- --- ------­

necessary distance toward a buoy placed in the center of

the reef. Percent B. yetrucosa in each zone was measured

during independent circumnavigations of the reef,

resulting in an unequal number of samples for each zone.

Preliminary plots of the cumulative percent of

43

H. verrucosa against the number of quadrats were made to

evaluate the adequacy of the sample size.

Percent time spent in different zones by

~. unimaculatus was estimated by establishing a grid

system, 20 m x 20 m, delineated at 5 m intervals with

colored bricks, on a portion of Patch Reef #42 (Area A on

Figure 2). Fish that were feeding on the grid system were

followed for a 10 minute period, and time spent in each of

5 zones «5 m from the edge, 5-10 m, 10-15 m, 15-20 m, and

20+ m from the edge) was recorded. This section of Patch

Reef #42 supports approximately 35-40 ~. unjmaculatus,

milling in large aggregations at the slope, and moving up

on the reef top in smaller groups to feed.

RESULTS

As is evidenced by the range in coral cover on

different reefs (Table 14, Figure 3), reefs representing a

gradient in total coral cover were selected. However,

although there is a correlation (r=0.876) between the

number of ~. unjmaculatus per meter of reef perimeter

(transformed by the. natural logarithm) and the percent

H.-yerrucosa on--the-patch I'eef-mars-in (transformed using

the arcsine function), the graph of this association

demonstrates the non-bivariate nature of the data (Figure 4).

44

TABLE 14. -- Comparison of coral cover and ~. unimacu1atus population size on selected p~tch reefs in Kane'ohe Bay (n=quadrat or census)

Reef % total no. coral

42 91.09 std. dev • 16.41

n 64

43 .

30

40

39

31

28

27

22

26

24

21

87.07 18.79· 56

74.54 29.82 92

55.27 31.34 27

40 .. 24 36.12 36

38.22 36.90 59

25.45 17.66 49

18.42 20.17 42

16.78 10.63 20

8.26 6.69

43

6.44 5.18

38

5.61 3.67

19

14.06 29.38' 64

14.72 25.78 56

2.21 9.10

92

o

2 .. 20 , 9.03

.36

0.74 2.09

59

0.41 0.96

49

0.12 0.29

42

0.99 1.38

20

0.04 0.18

43

0.28 0.87

38

0.35 1.15

19

45

no.~. peri- no. fish unimac. meter(m) per m

168.3 25.9 19

152 •. 3 15.7

9

9.4 1.6

10

2.6 1.7

10

8.3 2.1 7

15.4 4.1 7

10.2 4.1

12

2.0 1.4

14

o

14

6.1 2.9

14

3.0 2.9

12

2.5 1.3

15

484

564

437

163

376

478

370

346

94

346

286

66

0.3477

0.2700

0.0210

0.0159

0.0220

0.0323

0.0277

0.0058

o

0.0170

0.0150

o • 0374

Figure 3. -- Total coral cover and number of ~.

unimaculatus on selected patch reefs in Kane10he Bay.

46

N

... •

0 0 0 ..,

., ... ..

0 0 0 N

0 0 0

0 .., •

0:: IJJ

0 >

t-

O

(,)

0 -'

II> «

0 .. 0::

• 0 (,)

..J « I-

10> 0

'" ;;; .

l-•

it!

CD N

• to-

Q

N

N

• ~

CD ~

N

;;; . ... N

• •

Figure 4. -- Percent B. verrucosa and number of ~. unimaculatus on selected patch reefs in K~ne'ohe Bay.

48

.., 'I

* •

o -: o ot

III

0 .. 0 Co)

::a ... ... • :>

ID

~I

at

'"

In spite of ari effort to se~ect reefs ranging from

high to low coral cover, percent ~. verrucosa is high for

two patch reefs, 142 and 143, and low for the remaining

reefs. Although not reflected in the population estimates

for ~. unimaculatus on different reefs, a difference in

size of individuals on different reefs was noted. Patch

reefs.in the central portion of the bay, for example, 119,

120, 121, 123, and 124, characteristically supported small

to medium sized fish «10 cm total length). Patch reefs

#42 and #43 averaged larger fish (>12 cm total. length).

For both Patch Reef #42 and 143 there is an increase in

the percentage of B. yerrucosa with increased distance

from the edge of the reef (Table 15). A Kruskall-Wallis

test shows significant differences in the mean values of

B. yerrucosa for the different distances from the edge of

the reef.

TABLE 15. -- Percent cover of ~. verrucosa with increasing distance from the edge of Patch Reefs #42 and #43.

Reef No.

42 std.dev.

n - - - -- ~------ - -- -- ---- -----

43 std. dev.·

n

Distance from edge (m) o 5 10

14.06 29.65 53.46 29.38 36.20 28.79 64 58 37

--------------- ------ --------------- -

14.72 14.78 25.15 25.78 20.77 27.27 56 45 42

15

64.27 27.92 42

30.56 31.50 37

Time spent in each zone on Patch Reef 142 shows a

pattern of increase to a maximum at 10-15 m in from the

edge, with more than 50% of the time spent less than 15 m

50

from the edge (Table 16). It may be argued that an

observer may prevent fish from moving up slope, but

these fish appeared to have been habituated to my

presence, as many feeding observations of this

aggregation had been made previously. It should also be

noted that several fish were followed approximately 30-

35 m in towards the center of the reef, where they

proceeded to feed in a normal manner on ~. verrucosa.

TABLE 16. -- Comparison of time spent by ~. unimaculatus in concentric zones on Patch Reef #42 (19 observation periods) •

Zone (m from edge) Percent time

<5 20.7 '

5-10 29.0

DISCUSSION

10-15 30.2

15-20 11.4

20+ 8.6

As predicted for a 'specialized feeder, the distribution

of ~. unimaculatus is positively correlated with that of

its preferred food on the basis of comparisons between

reefs. This is similiar to results found for another

corallivorous chaetodontid in the Caribbean. The local

abundance of ~. capistratus was found to be positively

correlated the the index of diversity of coral and the

percent of total coral cover in two areas (Birkeland &

Neudeck~r, 1981). ~. capistratus is not a specialized

corallivore and browses from a variety of coral species;

therefore its abundance would be predicted to follow total

coral abundance.

However, within reefs the distribution of fish and

51

coral are not positively correlated. The increase in

M. verrucosa with increased distance from the edge of

Patch Reefs #42 and #43 and the distribution of activities

of the fish is consistant with the hypothesis that

predation or the perception of danger may have an effect

on time spent by ~. Ynimaculatus further from the reef

slope. It is possible that ~. Ynimaculatus relies on deep

cracks between the blocks of ~. ~mpressa on the slope for

protection: this is also supported by anecdotal

observations on the behavior of ~. unimaculatus in

response to the presence of large predatory fishes. On

one occasion in the early morning, as I was making feeding

observations, all ~. Ynimaculatus upslope from my position

rapidly swam back to the reef margin. Seconds later a

large barracude appeared from the central portion of the

reef, sw imming toward the edge.

52

CHAPTER V. CONCLUSION

It has been shown ••• that there are some species of large fish, and the whole tribe of Holothuriae which prey on the tenderer parts of corals. On the other hand, the polypifers in their turn must prey on some other organic beings •••• The relations, therefore, which determine the formation of reefs on any shore, by the .vigorous growth of the efficient kinds of coral, must be very complex, and with our imperfect knowledge quite inexplicable. (Darwin [1842] 1962:pp.63)

The elements which determine the structure and

species composition of coral reefs are complex. In the

northern end of Kane'ohe Bay, patch reefs are

characterized by high. coral coverage, primarily two

species, .l!. compresa and .M.. verrucosa. In areas where

coral coverage is high and space is at a premium, physical

factors, such as temperature· cycles, water flow

characteristics, salinity and light regimes, are

undoubtedly important in determining coral community

structure. However, because of the high percentage of

space occupied by coral, biological factors, such as

competition and predation, should also playa role in

determining community structure.

On the basis of growth rates and published accounts of

aggressive dominance,-it- would be predicted that

H. verrucosa would be the superior competitor of the two

common species in Ka.ne'ohe Bay and therefore should

monopolize more space on these patch reefs. However,

M. verrucosa comprises only about 15% of the cover at the

edge of patch reefs #42 and #43, which have high coral

53

coverage.

~. YDimaculatus is abundant on these same patch reefs

and is a selective coral feeder, chosing ~. verrucosa in

preference to ~. ~mpressa. This fish is commonly

observed milling around the edges of patch reefs, possibly

to remain near shelter provided by the deep cracks between

large blocks of ~. ~IDpressa. ~. YniIDaculatus makes

feeding forays up onto the tops of these patch reefs but

returns to the edge when a threat is perceived; for

example, the presence of a human snorkeler or a large

predatory fish. This study has shown that grazing by this

fish inhibits the growth of ~. yerrucosa and that

heavy grazing pressure (as observed in uncaged colonies

placed on the reef margin) can cause reversals of the

predicted aggressive dominance. Thus~. Ynimaculatus can

affect the outcome of competition for space on these

crowded patch reefs.

M. yerrucosa can grow at a variety of depths

(Maragos, 1972) and is found at different depths within

Kane'ohe Bay (personal observation); e.g. the slopes of

Patch Reefs #43 and #31 were dredged for the main ship

channel and ~. yerrucosa can be found down these dredged -- ---- ---- - - - --- ----- ~-- -- - -- - - --

slopes. On the slope of Patch Reef #31, ~. yerrucosa

occurs in isolated colonies, possibly not providing a type

of suitable shelter for ~. Ynimaculatus. On Patch Reef

#43, a dense mat of M. yerrucosa without crevices grows

on the dredged slope, again perhaps lacking appropriate

54

shelter for the fish.

The strict preference for M. verrucosa, as evident in

this Kane'ohe Bay study, suggests a possible reason for

low abundances of this fish species in other locations in

Hawai'i (personal observations). A minimum coverage of

the favored species or other acceptable coral food may be

a necessary requirement to support a large population of

~. Ynimaculatus: a condition satisfied by the high coral

coverage in the north end of Kane'ohe Bay.

~. Ynimaculatus is also unique in terms of foraging

behavior of chaetodontids in Hawai'i. It has a

specialized mouth which allows it to remove skeletal

material as well as coral tissue. This is a more

destructive type of feeding behavior than is generally

associated with chaetodontids and may cause more severe

impacts on corals. The pattern of distribution of

.M. ~.I..I..u~..aa.on Patch Reefs #42 and #43 may result from

the presence of a refuge from grazing and good physical

conditions for growth on the interior of these reef tops

combined with the presense of abundant shelter for

~. Ynimaculatus among the crevices on the reef slopes.

55

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60