Reef-associated fauna in Chesapeake Bay: Does oyster species affect habitat function? H. Harwell* 1, P. Kingsley-Smith 2, M. Kellogg 3, K. Paynter, Jr. 3 and M. Luckenbach 1. 1 Virginia Institute of Marine Science, The College of William & Mary 2 South Carolina Department of Natural Resources, 3 University of Maryland Illustration by Kent Forrest, © VIMS

Complexity Abundance Macroinvertebrate densities and species richness are generally positively correlated with structural complexity (Crowder and Cooper 1982, Diehl 1992). The Role of Habitat Complexity: Structurally complex habitats offer a greater variety of different microhabitats and niches, allowing more species to co-exist and contribute to within habitat diversity (Pianka 1988, Levin 1992). The importance of habitat heterogeneity / complexity has been investigated in many marine systems, including coral reefs, seagrass beds, rocky intertidal, mangroves, macroalgae, and oyster reefs.

C. virginica C. ariakensis Photo credits: Mark Luckenbach C. ariakensis C. sikamea Does habitat complexity vary between oyster species? If so, how will these differences affect habitat utilization?

Compare the complexity of experimental C. ariakensis and C. virginica reefs by examining vertical relief and surface complexity. Evaluate and compare the utilization of experimental C. ariakensis and C. virginica reefs by other organisms. Investigate the relationship between the development of reef associated communities and habitat complexity. Objectives

Experimental Design 4 sites in Chesapeake Bay 4 experimental “reef” treatments at each site: - triploid C. virginica only - triploid C. ariakensis only - 50% C. v. & 50% C. a - Shell only 2 replicates of each treatment per site Treatments placed in cages for biosecurity Each cage has a matrix of 5 x 5 trays

Atlantic Ocean Chesapeake Bay Delaware Bay SEVERN RIVER Subtidal (3 - 4m) Low salinity ( mean daily psu) Low predation pressure Low Dermo / No MSX PATUXENT RIVER Subtidal (3 - 4m) Low salinity ( mean daily psu) Moderate predation pressure Low Dermo / No MSX YORK RIVER Subtidal (1 - 2m) Mid salinity ( mean daily psu) High predation pressure High Dermo / High MSX MACHIPONGO RIVER Intertidal High salinity (5 -33 mean daily psu) High predation pressure High Dermo / Low MSX

Sampling Procedure

Quantifying Habitat Complexity maximum vertical height average ‘reef’ height (n = 10) surface rugosity index

Statistical Analysis 2-way ANOVA’s: Site and treatment effects on macrofaunal abundance, biomass, species richness, species evenness, and Shannon- Wiener diversity. Indices of habitat complexity (maximum and average vertical heights, surface rugosity) between sites and treatments. Nonparametric multi-dimensional scaling (MDS) and Analysis of Similarity (ANOSIM) to evaluate variations in community structure between treatments. Data were log transformed when necessary to meet assumptions of normality and homogeneity of variance. Pair-wise comparisons were conducted via Tukey’s tests.

Severn Patuxent York Machipongo FactorFpTukey Comparisons Site < York A, Patuxent A, Severn A, Machipongo B Patuxent A, York A, Severn B, Machipongo C Treatment < C.a. A, mix A, C.v. A, shell B C.a. A, mix A, C.v. B, shell C Site*Treatment < Treatment effects driven by YR and PR sites

Habitat Complexity: Surface Rugosity Severn (low salinity) Patuxent (mid salinity) York (high salinity) Machipongo (high salinity, intertidal) FactorFpTukey Comparisons Site21.46< York A, Severn B, Patuxent B, Machipongo C Treatment29.54< C.a. A, mix A, C.v. A, shell B Site*Treatment Treatment effects most pronounced at York

Severn (low) Patuxent (mid) York (high) Machipongo (high, intertidal) # of species # of dominant taxa Total # of associated organisms 17,00932,41940,6954,311 Total biomass of associated fauna (g) Total oyster biomass (g) Between-sites Comparison of Reef-associated Fauna July 2006

Dominant Reef-associated Fauna Species Richness: Lowest Species Evenness: Intermediate Diversity: Lowest Species Richness: Highest Species Richness: Intermediate Species Evenness: Intermediate Species Evenness: Lowest Species Evenness: Highest Diversity: Highest Diversity: Lowest F = p < F = 59.94p < F = 64.38p < 0.001

Mean total number of organisms per tray SevernPatuxentYorkMachipongo A AB BC >> > (F = , p < 0.001) F = p = (high salinity > mid salinity > low salinity > high salinity, intertidal) Total Number of Organisms

Mean abundance per gram of oyster biomass FactorFpTukey Comparisons Site23.97<0.0001Machipongo A, Patuxent B, York B, Severn B Treatment C.v. A, C.a. B, mix B Site*Treatment Treatment effects driven by PR and YR sites Standardized Total Abundance

SpeciesF p Tukey Comparisons C. equlibra C.v. A mix B C.a. B C. penantis C.v. A mix B C.a. B C. lacustre C.v. A mix AB C.a. B E. levis C.v. A mix B C.a. B G. mucronatus C.v. A mix B C.a. B P. tenuis C.v. A C.a. B mix B D. microphthalmus C.v. A C.a. B mix B H. dianthus C.v. A C.a. B mix B N. succinea C.v. A C.a. B mix B P. gouldii C.v. A mix B C.a. B C. sapidus C.v. A C.a. AB mix B M. tenta C.v. A mix B C.a. B M. arenaria C.v. A mix AB C.a. B G. strumosus C.v. A mix B C.a. B G. bosci C.v. A mix B C.a. B H. hentz C.v. A mix AB C.a. B B. bisuturalis C.v. A mix B C.a. B C. fornicata C.v. A mix AB C.a. B R. punctostriatus C.v. A mix B C.a. B U. cinerea C.v. A mix B C.a. B

Conclusions Changes in both faunal assemblages and habitat complexity indices were more pronounced between sites than within sites. In mid to high salinity subtidal sites, C. virginica’s ability to support higher abundances of associated fauna per unit of oyster biomass may be offset by: C. virginica ‘reefs’ supported higher abundances of over 20 different species of associated fauna per unit oyster biomass compared to C. ariakensis ‘reefs’. ‘Reefs’ containing both oyster species most often supported abundances similar to those of non-native ‘reefs’, illustrating a possible effect of multi-species reefs, should C. ariakensis be introduced. Higher growth rates of C. ariakensis, resulting in higher oyster biomass per area of oyster bottom. Higher average reef height of C. ariakensis reefs.

ESL: Brian Barnes, Alan Birch, Reade Bonniwell, Stephanie Bonniwell, Roshell Brown, Al Curry, Sean Fate, PG Ross, Edward Smith, Jamie Wheatley ESL Summer Aides: Raija Bushnell, Ben Hammer, Sarah Mallette, Andrew Matkin, Andrew Wilson UMD: Steve Allen, Marcy Chen, Jake Goodwin, Mark Sherman, Nancy Ward UMCES Horn Point: Stephanie Tobash, Angela Padaletti VIMS ABC: Katie Blackshear, Shane Bonnot, Ryan Gill, Karen Hudson Statistical and taxonomic assistance: David Gillett Acknowledgements