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Reef-associated fauna in Chesapeake Bay: Does oyster species affect habitat function? H. Harwell*1, P. Kingsley-Smith2, M. Kellogg3, K. Paynter, Jr.3 and M. Luckenbach1. 1Virginia Institute of Marine 2South Carolina Department 3University Science, The College of William & Mary of Natural Resources, of Maryland Illustration by Kent Forrest, © VIMS 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. Abundance • Macroinvertebrate densities and species richness are generally positively correlated with structural complexity (Crowder and Cooper 1982, Diehl 1992). Complexity Does habitat complexity vary between oyster species? C. sikamea If so, how will these differences affect habitat utilization? C. ariakensis C. virginica C. ariakensis Photo credits: Mark Luckenbach Objectives 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. 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 Delaware Bay SEVERN RIVER Subtidal (3 - 4m) Low salinity (3 - 14 mean daily psu) Low predation pressure Low Dermo / No MSX PATUXENT RIVER Subtidal (3 - 4m) Low salinity (8 - 16 mean daily psu) Moderate predation pressure Low Dermo / No MSX Chesapeake Bay YORK RIVER Subtidal (1 - 2m) Mid salinity (9 - 21 mean daily psu) High predation pressure High Dermo / High MSX Atlantic Ocean 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 ShannonWiener diversity. • Indices of habitat complexity (maximum and average vertical heights, surface rugosity) between sites and 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. • Nonparametric multi-dimensional scaling (MDS) and Analysis of Similarity (ANOSIM) to evaluate variations in community structure between treatments. 80 C. virginica C. ariakensis 60 Total number of live oysters across all cages Machipongo River, VA July 5th 2006 40 20 80 C. virginica C. ariakensis York River, VA July 24th 2006 60 Total number of live oysters across all cages 40 20 80 C. virginica C. ariakensis 60 Total number of live oysters across all cages Patuxent River, MD July 10th 2006 40 20 80 C. virginica C. ariakensis 60 Total number of live oysters across all cages Severn River, MD July 17th 2006 40 20 0 30 60 Shell length (mm) 90 120 Severn Height from top of tray (cm) 8 6 6 4 4 2 2 0 0 C. ariakensis C. virginica mixed shell York 8 C. ariakensis 6 4 4 2 2 0 C. virginica mixed shell Machipongo 8 6 0 C. ariakensis C. virginica mixed shell maximum 'reef' height Factor Patuxent 8 F p C. ariakensis C. virginica mixed shell mean 'reef' height Tukey Comparisons Site 25.95 < 0.0001 46.32 <0.0001 YorkA, PatuxentA, SevernA, MachipongoB PatuxentA, YorkA, SevernB, MachipongoC Treatment 36.11 < 0.0001 68.29 < 0.0001 C.a.A, mixA, C.v.A, shellB C.a.A, mixA, C.v.B, shellC Site*Treatment 5.58 7.76 < 0.0001 Treatment effects driven by YR and PR sites < 0.0001 Treatment effects driven by YR and PR sites Habitat Complexity: Surface Rugosity Severn (low salinity) Surface rugosity Index 1.6 1.6 1.4 1.4 1.2 1.2 1 Patuxent (mid salinity) 1 C. ariakensis C. virginica mixed shell York (high salinity) 1.6 C. ariakensis 1.6 1.4 1.4 1.2 1.2 1 C. virginica mixed shell Machipongo (high salinity, intertidal) 1 C. ariakensis C. virginica mixed shell C. ariakensis C. virginica mixed shell Factor F p Tukey Comparisons Site 21.46 < 0.0001 YorkA, SevernB, PatuxentB, MachipongoC Treatment 29.54 < 0.0001 C.a.A, mixA, C.v.A, shellB Site*Treatment 5.25 0.0003 Treatment effects most pronounced at York Between-sites Comparison of Reef-associated Fauna July 2006 Severn Patuxent York Machipongo (low) (mid) (high) (high, intertidal) 22 35 63 48 # of dominant taxa Total # of associated organisms 8 17,009 6 32,419 12 40,695 16 4,311 Total biomass of associated fauna (g) 167.95 571.05 213.20 31.71 Total oyster biomass (g) 456.11 781.72 1371.05 22.59 # of species Dominant Reef-associated Fauna Severn (low salinity) 1 Species1 Richness: Lowest Species Evenness:3 Intermediate Diversity: Lowest York (high salinity) Patuxent (mid salinity) 1 Species Richness: Intermediate 2 1 Species Evenness: Lowest 2 Diversity: Lowest Machipongo (high salinity, intertidal) Species Richness: Highest 4 Species Evenness: Intermediate 2 3Intermediate Species Richness: 5 Evenness: Highest Species Diversity: Diversity: 4 polychaetes bivalves Highest 1 Famphipods = 192.75 p < 0.001crabs F = 59.94 p < 0.001 gastropods F = 64.38 p < 0.001 fishes Highest other Mean total number of organisms per tray Total Number of Organisms 2500 A F = 101.91 p = 0.001 AB 2000 B C mixed shell 1500 1000 500 0 C. ariakensis C. virginica York > Patuxent > Severn > Machipongo (high salinity > mid salinity > low salinity > high salinity, intertidal) (F = 101.91, p < 0.001) Mean abundance per gram of oyster biomass Standardized Total Abundance Patuxent (mid salinity) Severn (low salinity) 50 140 120 40 100 30 80 20 60 40 10 20 0 0 C. ariakensis mixed species York (high salinity) 250 C. ariakensis C. virginica 4000 B 200 mixed species C. virginica Machipongo (high salinity, intertidal) 3000 150 2000 100 A A 1000 50 0 0 C. ariakensis mixed species C. virginica C. ariakensis mixed species C. virginica Factor F p Tukey Comparisons Site 23.97 <0.0001 MachipongoA, PatuxentB, YorkB, SevernB Treatment 6.00 0.0045 C.v.A, C.a.B, mixB Site*Treatment 5.25 0.0003 Treatment effects driven by PR and YR sites Species D. microphthalmus H. dianthus N. succinea P. gouldii C. equlibra C. penantis C. lacustre E. levis G. mucronatus P. tenuis C. sapidus M. tenta M. arenaria G. strumosus G. bosci H. hentz B. bisuturalis C. fornicata R. punctostriatus U. cinerea F 29.34 4.33 7.41 4.55 8.78 5.78 8.06 9.62 8.99 7.62 4.09 4.19 6.60 28.82 9.95 3.18 31.23 5.47 11.08 6.57 p 0.0001 0.0181 0.0015 0.0150 0.0005 0.0054 0.0009 0.0003 0.0004 0.0012 0.0223 0.0204 0.0028 0.0001 0.0002 0.0498 0.0001 0.0069 0.0001 0.0028 Tukey Comparisons C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.v.A C.a.B C.a.B C.a.B mixB mixB mixB mixAB mixB mixB C.a.B C.a.AB mixB mixAB mixB mixB mixAB mixB mixAB mixB mixB mixB mixB mixB C.a.B C.a.B C.a.B C.a.B C.a.B C.a.B mixB mixB C.a.B C.a.B C.a.B C.a.B C.a.B C.a.B C.a.B C.a.B C.a.B Severn (low salinity) stress: 0.07 Patuxent (mid salinity) Global R: 0.349 York (high salinity) Global R: 0.602 stress: 0.02 stress: 0.03 Significance Level: 0.2% Machipongo (intertidal) stress: 0.05 Significance Level: 0.1% C. ariak ensis C. virginica 50 C.ariak ensis : 50 C. virginica Conclusions • Changes in both faunal assemblages and habitat complexity indices were more pronounced between sites than within sites. • C. virginica ‘reefs’ supported higher abundances of over 20 different species of associated fauna per unit oyster biomass compared to C. ariakensis ‘reefs’. • 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: • Higher growth rates of C. ariakensis, resulting in higher oyster biomass per area of oyster bottom. • Higher average reef height of 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. Acknowledgements • 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