Molluscan (Shellfish) Studies | Coastal Fisheries Surveys & Monitoring

The significance of molluscs to the estuarine ecosystem has long been recognized. Over one hundred years ago the concept of an ecological community was developed through observations of the faunal assemblages of oyster reefs. Functionally, molluscs serve as a key trophic link between primary producers and higher consumers. Bivalves in particular are important as biogeochemical agents in benthic-pelagic coupling, cycling organic matter from the water column to the bottom. In addition, molluscs can have a pronounced impact on the physical structure of an ecosystem, whether by reworking the sediment, grazing, binding or securing existing substrate, or building new substrate such as oyster reefs. Lastly, many molluscs are commercially valuable, both directly as a harvestable resource and indirectly as a food source for commercially and recreationally important species including crabs, fish, and waterfowl.

The MDNR Shellfish Division has been conducting molluscan shellfish projects in the Coastal Bays since 1993. The initial study was a molluscan inventory, sampling in a wide range of habitats (remnant oyster shell bars, soft substrates, seagrass, salt-marsh fringe, man-made structures) using a variety of methods. This comprehensive inventory was completed in 1996, resulting in a catalogue of the molluscan fauna of Maryland's coastal bays and tributaries; information and spatial comparisons on species distribution, abundance, and population structure among the components of the coastal bays system; a characterization of the temporal variability of molluscan populations in Chincoteague Bay; documentation of mollusc-habitat associations; and a review the ecological roles of the dominant molluscan species. One of the most striking findings was the absence of oysters, except for isolated pockets in the intertidal zone. Several species not previously recorded from the Coastal Bays were identified, including the northward range extension of three southern species, possibly a reflection of climate change.

The annual MDNR Hard Clam Survey developed out of this study, which maintains aspects of the original inventory but is based on the use of a commercial hydraulic escalator dredge as a sampling gear. The results of this survey, which has continued to the present, provided supporting information for the Hard Clam Fishery Management Plan and serves as one of the components of the recently initiated Coastal Bays report card evaluating the health of this ecosystem. In addition, experimental work has been conducted on improving hard clam habitat through shell plantings and reclamation of buried shell.

In an attempt to re-establish a population in Chincoteague Bay, MDNR Shellfish Program planted 1.2 million bay scallops and raised them to reproductive age during 1997 and 1998. By 2002, live scallops were recorded north of the Ocean City Inlet, both in Isle of Wight and Assawoman Bays, possibly for the first time in well over a century. Although low densities suggest that the long-term viability of the bay scallop population is still tenuous, the extraordinarily rapid range expansion is a major step toward their establishment in the coastal bays.

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