Habitat complexity and habitat function of native (Crassostrea virginica) and non-native (C. ariakensis) oysters in the Chesapeake Bay region
Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Stan Allen, Jr
Complex oyster reefs created by the Eastern oyster, Crassostrea virginica, though once prominent features of the Chesapeake Bay region, have become relatively scarce in comparison to historic descriptions. This decline, caused by a combination of overfishing, disease, habitat destruction and pollution, this decline continues despite substantial restoration efforts that have spanned decades. In response to this decline, the states of Virginia and Maryland considered the intentional introduction of the non-native Suminoe oyster, C. ariakensis. Previous studies questioned the reef-building capability of this Crassostrea species, which may affect its habitat function. Through a combination of field and mesocosm studies, I examined the possibility that this non-native oyster species would provide an ecologically-functional equivalent of the native oyster species if introduced into Chesapeake Bay. Habitat complexity and associated benthic communities of experimental triploid C. virginica and C. ariakensis reefs were investigated at four sites of varying salinity, tidal regime, water depth, predation intensity and disease pressure in the Chesapeake Bay region (Virginia and Maryland). Four experimental treatments were established at each site: C. virginica; C. ariakensis; 50:50 of C. virginica: C. ariakensis; and shell only. Abundance, biomass, species richness, evenness, dominance and diversity of reef-associated fauna were evaluated in relation to habitat location and oyster species over a period of 21 months. Habitat complexity varied spatially, although no differences among complexity indices were associated with oyster species. Increases in vertical reef heights and surface rugosity were observed over time for all experimental reefs, and treatment effects were observed after 19 months of development, when C. ariakensis reefs exceeded the vertical heights of C. virginica reefs, removing any doubt regarding the Suminoe oyster's reef-building capability. Spatial comparisons of reef-associated macrofauna suggested functional equivalency between oyster species with respect to habitat at intertidal locations (where C. ariakensis survival was low), and at subtidal sites of low salinity. at subtidal locations of higher salinities, however, the numbers of organisms associated with C. virginica reefs per unit of oyster biomass were significantly greater than the numbers of organisms associated with C. ariakensis. Multivariate analyses of data from subtidal high salinity sites also revealed unique communities associated with C. virginica treatments, while mixed oyster species assemblages were functionally equivalent to mono-specific C. ariakensis experimental treatments. Temporal comparisons at one mesohaline subtidal site revealed that the observed effects of oyster species on habitat function in higher salinity locations are inconsistent over time and likely overshadowed by seasonal larval recruitment dynamics and local hydrodynamics. Though a common oyster reef trophic cascade between juvenile oysters, C. virginica; mud crabs, Panopeus herbstii; and oyster toadfish, Opsanus tau was successfully replicated during mesocosm trials, specific trophic interactions were not significantly affected by oyster substrate species or habitat complexity (as it was defined within the constraints of the experiment). Together, these experiments represent the first effort to quantify the potential habitat function of C. ariakensis in Chesapeake Bay, and provide evidence of species-specific similarities and differences in reef-associated communities.
© The Author
Harwell, Heather D., "Habitat complexity and habitat function of native (Crassostrea virginica) and non-native (C. ariakensis) oysters in the Chesapeake Bay region" (2010). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539616687.
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