interactions of top down and bottom up forces and habitat complexity in experimental oyster reef...

Interactions of Top Down and Bottom Up Forces and Habitat Complexity in Experimental

Oyster Reef Microcosms

William S. Rodney, Lisa Kellogg & Kennedy T. Paynter

Talk Structure:Talk Structure:

I.I. System DescriptionSystem Description

II.II. Experimental Results Experimental Results

Talk StructureTalk Structure

I.I. System DescriptionSystem Description

II.II. Experimental ResultsExperimental Results

Oyster Reef Ecological Functions:

(1) water filtration and regulation of water column phytoplankton dynamics.

(2) enhanced nitrogen cycling between the benthic and pelagic system components.

(3) enhanced recruitment, growth, and survival of oyster populations and a revitalized fishery.

(4) nursery and predation refuge habitat for a diverse community of invertebrates and small fishes.

(5) foraging habitat for transient fish predators.

BB

A typical unrestored oyster reef (A) as compared to a typical restored oyster reef (B).

A

The Study System: Subtidal Mesohaline Oyster Bars in Chesapeake Bay, Maryland.

Some Key Players:

Mean Density of Functional Groups Based on Substrate Use. Blue Bars = Restored, Green Bars = Unrestored, Error bars represent +/- 1 SEM. Asterisks Indicate Statistical Significance..

Infauna

Epifauna*

All Free Living Fauna*

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

Fau

nal

Gro

up

Organisms / m2

Mean Densities of Dominant Taxa

Demersal Fish*

Amphipods*

Polychaetes

N. succinea*

Clams

M. balthica

M. arenaria

Xanthid Crabs*

0 200 400 600 800 1000 1200 1400 1600 1800

Fau

nal

Gro

up

Organisms / m2

Mean Biomass Density of Dominant Taxa

0 50 100 150 200 250

Fau

nal

Gro

up

Grams / m2

Clams

Amphipods (x10)*

N. succinea*

Xanthid Crabs*

Demersal Fish*

Grass Shrimp*

Functional Feeding Groups

0 2000 4000 6000 8000 10000

Func

tiona

l Gro

up

Organisms / m2

Carnivore/Omnivores*

Suspension Feeders*

Surface Deposit Feeders

Deep Deposit Feeders (x100)*

Macrofauna Biomass (g) Energy (Fish Food!)

Faunal Group AFDW/WW (%) kcal/g AFDW

Polychaetes:

N. succinea 16.501 6.0702

P. gouldii 14.001 6.0702

Clams 0.087*1 5.7832

Amphipods 16.01 5.2022

P. pugio 16.501 6.3932

Xanthid Crabs 16.50 4.3033

Demersal fish 32.102 5.9002

(* =SFDW, 1 Ricciardi & Bourget 1998, 2 Thayer et al. 1973, 3 Wissing et al. 1973)

Macrofaunal Energy Density

Restored

Unrestored

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

Treatment

Mea

n E

Den

sity

(J*m

-2)

Talk StructureTalk Structure

I.I. System DescriptionSystem Description

II.II. Experimental ResultsExperimental Results

Research Questions: How can oyster reefs simultaneously function

as both nursery and predation refuge habitat for macrofauna and as fish predator foraging habitat ?

Are deposit feeder densities similar in restored and unrestored habitats because this group isn’t affected by restoration or is there some other reason? (e.g., Bottom Up vs. Top Down Factors and Habitat Complexity)

Experimental Design:Experimental Design:3 x 2 x 2 Factorial ANOVA3 x 2 x 2 Factorial ANOVA

Factor Levels

Substrate Sediment (Low Complexity)

Half Shell (Moderate Complexity)

Clump (High Complexity)

Energy Source + Biodeposits

(Bottom Up) Control (natural seston)

Predation Predators Present

(Top Down) Predators Absent

Factor = Structural Complexity:Factor = Structural Complexity:

Sediment Half Shell Clump (Reef)

Factor = Energy SourceFactor = Energy Source

The Feces Factory (Oyster Biodeposits Collector)

Factor = PredationFactor = Predation

Naked Goby (Gobiosoma bosc)

The Response Variable: Melita nitidaThe Response Variable: Melita nitida

Microcosm Experiment

The Microcosm Array

3x2x2 Factorial ANOVADependent Variable: log amphipod abundance Sum of Source DF Squares Mean Square F Value Pr > F

Model 11 13.971 1.270 16.43 <.0001 Error 36 2.783 0.077 Corrected Total 47 16.755 R-Square Coeff Var Root MSE logamphs Mean 0.833866 19.51354 0.2786 1.424991 Source DF Type I SS Mean Square F Value Pr > F Substrate 2 3.60534590 1.80267295 24.39 <.0001 Esource 1 1.68953482 1.68953482 22.86 <.0001 Predators 1 5.26410821 5.26410821 71.22 <.0001 Substrate*Esource 2 0.45876893 0.22938446 3.10 0.0574 Esource*Predators 1 0.38745329 0.38745329 5.24 0.0282 Substrate*Predators 2 2.28477170 1.14238585 15.46 <.0001 Substr*Esourc*Predat 2 0.36087834 0.18043917 2.44 0.1017

Esource*Predators (p = 0.0282)Red Lines = + Predators, Green Lines = - Predators

0

20

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Mud Half Shell Reef

Am

phip

od A

bund

ance

0

20

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180

Mud Half Shell Reef

Control + Biodeposits

Effect of Oyster BiodepositsEffect of Oyster Biodeposits

+ Biodeposits

Control

0.00

20.00

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120.00

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160.00

Microcosm Treatment

Mea

n A

mph

ipod

Abu

ndan

ce

(am

phip

ods/

mic

roco

sm)

0

20

40

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Mud Half Shell Reef

0

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Mud Half Shell Reef

Predators Absent Predators Present

Am

ph

ipo

d

Ab

un

dan

ceSubstrate*Predators (p < 0.0001)Red Lines Mean Energy Soucre = Control

Green Lines Mean Energy Source = + Biodeposits

Conclusions: Addition of a moderate amount of oyster biodeposits

(OBD) had a profound effect on amphipod production. Amphipod abundance was 3.5 times greater in treatments that received OBD. The effect of OBD was modified by the presence of predators.

The effect of predators was mitigated by reef structural complexity. The combined effects of OBD and reef structure allowed for high amphipod production in the presence of predators.

The End!

Acknowledgments

I wish to thank: Mark Sherman, Sara Rowland and Paul Miller of the Paynter Lab.

Bud Millsaps, and various other CBL folks.