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Benthic Macrofauna in Narragansett Bay, Rhode Island: An Evaluation of Different Approaches for Describing Community Assemblages

Christopher J. Calabretta and Candace A. Oviatt

University of Rhode Island Graduate School of Oceanography, Narragansett, Rhode Island

Growing concern about the overall 'health' of coastal ecosystems in the presence of both natural and anthropogenic stressors has lead to increased efforts to monitor and assess status and trends in environmental condition. Benthic invertebrates have become well established as useful bio-indicators of ecological quality in coastal and estuarine environments. This study compared data collected using two different methodological approaches for sampling macrobenthic community assemblages. The sampling programs analyzed by this study were those used during the Marine Ecosystem Research Laboratory's Upper Narragansett Bay Benthic Study and those used during the U.S. Environmental Protection Agency's National Coastal Assessment (NCA). Inconsistencies identified between the results of each survey suggested that, at least in some instances, the method by which sediment is obtained for benthic community analysis will affect the story told by the resulting data as to the status of the benthos. Three main factors were identified which should be considered during the design of programs for sampling macrobenthic community assemblages: (1) the method used for sediment collection; (2) temporal variability in macrofaunal abundance; and (3) spatial variability in macrofaunal distribution. Among the likely causes for the discrepancies between these studies was an underestimate of opportunistic fauna during the NCA sampling caused by the use of a van Veen grab for sediment collection. Taking into consideration trends in benthic community structure, it is likely that the effects of surface sediment displacement inherent with van Veen grab sampling would become most evident during the interpretation of data for assemblages of opportunistic taxa while having little effect on the assessment of climax communities.

Keywords: benthic community analysis; ecological indicators; species diversity; abundance.

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