Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Linda C. Schaffner
Anthropogenic degradation of coastal and estuarine habitats is an ongoing problem facing scientists, natural resource mangers, and the general public. Decreases in habitat quality produce relatively predictable changes in the structure and composition of macrobenthic communities and it has traditionally been assumed that the ecosystem functions of the community change as well. In Chesapeake Bay, the most pervasive cause for the degradation of benthic habitats is the excessive inputs of nutrients that lead to eutrophication and the accumulation of organic matter in the system. Working within this framework, a study was conducted investigating changes in macrobenthic (i.e., secondary) production along a gradient of eutrophication-driven changes in habitat quality in shallow subtidal Chesapeake Bay. to determine if changes in macrobenthic community structure and function alter the food web of these systems, the effects of habitat quality on the utility of the macrobenthos as a food source to nekton via a predator exclusion experiment and a stable isotopic (15N and 13C) study on the diet of the macrobenthos and nekton were examined along a portion of the aforementioned gradient in habitat quality. There was strong evidence indicating that in depositional habitats of the saline estuary, macrobenthic 2?? production decreased with decreasing habitat quality. There was also some indication that in non-depositional habitats, water column eutrophication did not act as a stressor to the benthos; instead providing food subsidies to the macrobenthos and leading to an increase in community 2?? production (primarily filter-feeders). The predator exclusion experiment illustrated that changes in macrobenthic community structure and production had an impact on the suitability of the habitat as forage areas for benthivoric nekton. The degree of predation pressure was not, however, related to habitat quality. Instead it appears to have been related to the presence/absence of large amounts of bivalve production. Additionally, results indicate that bioturbation of sediments by nekton searching for prey items also had negative effects on the production of deep deposit-feeding and small interface-feeding fauna. Based upon the patterns in stable isotopes of the fauna and the organic matter pools, there was little impact of habitat degradation on consumption by most of the macrobenthic feeding guilds. There was some indication of prey/organic matter switching among the omnivores and shallow-deposit feeding fauna at different sites, but not in relation to habitat quality. Results also showed that most of the macrobenthos collected from shallow subtidal habitats were not dependent upon microphytobenthos as a primary food source. Isotopic values indicate that most of the macrobenthos were feeding upon a mix of microphytobenthos, phytoplankton, sediment, and detritus, all of which was likely processed, to some degree, by sediment bacteria. Considered together, these results illustrate how eutrophic-driven habitat degradation negatively impacts the functioning of shallow water estuarine food webs and that the impacts are realized through the macrobenthos. This dissertation provides evidence supporting the assumptions that ecosystem function can be linked to macrobenthic community structure and provides an avenue to incorporate changes of environmental quality into predictions about the productivity, and consequently, the management of natural resources.
© The Author
Gillett, David James, "Effects of habitat quality on secondary production in shallow estuarine waters and the consequences for the benthic-pelagic food web" (2010). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1539616666.