marsh terracing as a restoration technique for creating nekton habitat

Marsh terracing as a restoration technique for creating nekton

habitat

USGS Louisiana Cooperative Fish and Wildlife Research Unit

School of Renewable Natural ResourcesLouisiana State University Agricultural Center

Baton Rouge, LA

• To restore and increase vegetated marsh and submerged aquatic vegetation habitat in terms of both quantity and quality

– To increase fishery habitat in terms of area and quality

COASTAL RESTORATION

Field of dreams hypothesis:

“if you build it,

they will come”

• Area of vegetated marsh created

• Establishment of marsh vegetation

• Functional equivalency– Habitat quality (density, standing stock)– Habitat suitability (species occurrence)– Food chain support (diet)– Fitness (condition or growth)

MEASURING SUCCESS

• Determine the effect of marsh terraces on adjacent water quality and sediment characteristics.

• Compare nekton communities in paired terraced and unterraced ponds:– Density (habitat quality)– Community assemblages (habitat suitability)– Condition (fitness)

OBJECTIVES

• Rozas and Minello 2001– Maximize marsh edge

• Bush Thom et al. 2004– Differences in community composition

PREVIOUS TERRACE RESEARCH

• Three sets of paired terraced and unterraced ponds (Rockefeller SWR (Sites 1 &2); Sabine NWR (Site 3)).

• Sampling at three habitat types:1) terraced marsh edge 2) unterraced marsh edge 3) open water

• Sampled 7 times– bi-monthly April 2004 – April 2005

• 7 sample dates x 3 sites x 2 ponds x 4 sites = 168 samples

RS

Site 3Unit 7 (t)Unit 5 (u)

Site 2Unit 5 Site 1

Unit 4

STUDY SITES

Terraced Pond• Two terraced edge (< 1m)• Two open water (> 50 m edge)

Unterraced Pond• Two unterraced edge (< 1m)• Two open water (> 50 m)

• Nekton– Samples were collected with a 1-m2 throw trap. A bar

seine is used to clear all nekton from the trap.

METHODS

• Water Quality & Soils– Depth and water quality data (salinity,

conductivity, temp., D.O., turbidity) were collected along with each nekton sample.

– Percent organic matter

• SAV– All submerged aquatic vegetation was

collected from the throw trap.

METHODS

Habitat quality

Compare water quality, nekton density, biomass, richness and diversity between terraced and unterraced edge and open water sites (ANOVA)

Habitat Suitability

Compare species composition (Chi-square)

Nekton Condition

Compare dominant species length-weight relationships (ANCOVA)

STATISTICAL ANALYSES

• Turbidity (P = 0.23)– lower in terraced ponds

• SAV (P < 0.0001) – higher biomass in terraced ponds

• *Soil Organic Matter (P = 0.003)– lower at terraced edge

RESULTS: ENVIRONMENTAL CHARACTERISTICS

Craft et al. 2003

FUNCTIONAL EQUIVALENCY TRAJECTORY

0

5

10

15

20

25

30

35

40

45

Edge Open water Edge Open water

Habitat Type

Nek

ton

Den

sity

(in

div

idu

als/

m2 )

Terraced Unterraced

0

5

10

15

20

25

30

35

40

45

Edge Open water Edge Open water

Habitat Type

Nek

ton

Den

sity

(in

div

idu

als/

m2 )

Terraced Unterraced

A

B

0

5

10

15

20

25

30

35

40

45

Edge Open water Edge Open water

Habitat Type

Nek

ton

Den

sity

(in

div

idu

als/

m2 )

Terraced Unterraced

A

A

• Habitat characteristics differed between terraced and unterraced ponds (SAV, organic matter,

turbidity).

• Habitat quality, as measured by nekton density and diversity, were similar between terraced and unterraced edges.

CONCLUSIONS

Terraced

Daggerblade grass shrimp

Rainwater killifishInland silversideSailfin mollyNaked gobyBlue crabWestern mosquitofishOther

Unterraced

n = 1,623 n = 1,921

NEKTON SPECIES COMPOSITION

Chi-sq: P < 0.0001

Terraced Edge

Crustaceans

Demersal fish

Benthopelagic fish

Pelagic fish

Unterraced Edge

Terraced Open Water Unterraced Open Water

• Habitat characteristics differed between terraced and unterraced ponds (SAV, organic matter,

turbidity).

• Habitat quality, as measured by nekton density and diversity were similar between terraced and unterraced edges.

• Habitat suitability, as measured by species abundances and community composition, differed

significantly between terraced and unterraced habitats with greater proportion of benthic dependent species at unterraced edge, and greater proportions of pelagic species in terraced habitats.

CONCLUSIONS

• Based on length / weight relationship

• Heavier fish = better condition

-2.0

-1.5

-1.0

-0.5

0.0

log10(length)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

log10(weight)

Lucania parva

log10(W) = a' + b × log10(L)

W' = aLb

Kn = W / W'

FISH CONDITION

- 5

- 4

- 3

- 2

- 1

0

1

2

l og l engt h

- 0. 4 - 0. 2 0. 0 0. 2 0. 4 0. 6 0. 8 1. 0 1. 2 1. 4 1. 6

Cyprinodon variegatus ANCOVA

terracedunterraced

Condition (length-weight)

• Inland silverside

• Sheepshead minnow

• Clown goby

Unterraced TerracedNSD

• Rainwater killifish

• Western mosquitofish

• Naked goby

• Sailfin molly

• Habitat characteristics differed between terraced and unterraced ponds (SAV, organic matter, turbidity).

• Habitat quality, as measured by nekton density was similar between terraced and unterraced edges.

• Habitat suitability, as measured by species abundances and community composition, differed significantly between terraced and unterraced habitats.

• Nekton fitness or health, as measured by length – weight relationships, was lower in terraced as compared to unterraced ponds for 3 species, and similar between terraced and unterraced ponds for 3 different species.

CONCLUSIONS

FUNCTIONAL EQUIVALENCY TRAJECTORY

Time

Co

mp

lexi

ty /

fu

nct

ion

Alternative states

(Hobbs and Mooney 1993)

Stays the same

Continued decline

Restoration

Plant biomass (3-5 yrs); benthic communities (10-15 yrs); soil properties (30 + years) (Craft et al. 1999, Craft 2003, Broome et al. 1986)

• Terraces do provide nekton habitat, largely through the provision of edge habitat.

• However, ecological equivalency is clearly not achieved within 4 years of restoration (as measured in this project).

• Species occurrence or abundance only provide a part of the picture - measures of species health and community assemblages need to be considered to fully capture the “value” of restored marshes.

FUNCTIONAL EQUIVALENCY

• Funding provided by CREST (Coastal Restoration and Enhancement through Science and Technology)

• Thanks to Rockefeller SWR and Sabine NWR for access to sites, and logistical help.

• Thanks to Chris Cannaday, Jessica O’Connell, Bryan Piazza, Tim Birdsong, and Seth Bordelon for assistance in the field.