Date Awarded


Document Type


Degree Name

Master of Science (M.Sc.)


Virginia Institute of Marine Science


Aquaculture of the hard clam Mercenaria mercenaria is a valuable industry on the east coast. At high planting densities, cultured bivalves can become limited by food availability, resulting in reduced growth. Centric diatoms are considered the dominant food source to cultured bivalves. Alternative sources may also be important, including resuspended benthic microalgae (pennate diatoms) and detritus from macroalgae growing on predator exclusion nets. This study measured (1) the availability of different food sources in clam beds at Cherrystone Inlet in Chesapeake Bay, including the effects of macroalgae on food availability, and (2) the clearance rates and absorption efficiencies by cultured clams on individual and mixed food treatments in laboratory feeding experiments. Abundances of benthic microalgae (pennate diatoms) were similar to or greater than centric diatoms. Detritus availability under nets was related significantly to macroalgal abundance. Mass-specific clearance rates and absorption efficiencies were similar among food sources, but differences in the percentage of clams feeding on each treatment suggest macroalgal detritus was less utilized by clams than either phytoplankton or benthic microalgae. Both phytoplankton and benthic microalgae appeared to be valuable food sources to clams, both in terms of in situ abundance and relative food value indices calculated from feeding studies. Though food value was lower for macroalgal detritus, the high availability of this source to clams during blooms suggests it may be important seasonally. Lower diatom concentrations under nets compared to above during a macroalgal bloom suggest dense blooms may limit diatom availability to clams. Future modeling of cultured bivalve carrying capacity should consider the importance of multiple food sources in aquaculture environments.



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