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: I. System Description II. Experimental Results

Talk Structure I. System Description II. Experimental 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.

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.

Mean Densities of Dominant Taxa

Mean Biomass Density of Dominant Taxa

Macrofauna Biomass (g)  Energy (Fish Food!) Faunal GroupAFDW/WW (%)kcal/g AFDW Polychaetes: N. succinea P. gouldii Clams0.087* Amphipods P. pugio Xanthid Crabs Demersal fish (* =SFDW, 1 Ricciardi & Bourget 1998, 2 Thayer et al. 1973, 3 Wissing et al. 1973)

Macrofaunal Energy Density

Talk Structure I. System Description II. Experimental 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: 3 x 2 x 2 Factorial ANOVA FactorLevels SubstrateSediment (Low Complexity) Half Shell (Moderate Complexity) Clump (High Complexity) Energy Source+ Biodeposits (Bottom Up)Control (natural seston) PredationPredators Present (Top Down)Predators Absent

Factor = Structural Complexity: Sediment Half Shell Clump (Reef)

Factor = Energy Source The Feces Factory (Oyster Biodeposits Collector)

Factor = Predation Naked Goby (Gobiosoma bosc)

The Response Variable: Melita nitida

Microcosm Experiment The Microcosm Array

3x2x2 Factorial ANOVA Dependent Variable: log amphipod abundance Sum of Source DF Squares Mean Square F Value Pr > F Model <.0001 Error Corrected Total R-Square Coeff Var Root MSE logamphs Mean Source DF Type I SS Mean Square F Value Pr > F Substrate <.0001 Esource <.0001 Predators <.0001 Substrate*Esource Esource*Predators Substrate*Predators <.0001 Substr*Esourc*Predat

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

Effect of Oyster Biodeposits

Predators AbsentPredators Present Amphipod Abundance Substrate*Predators (p < ) 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.