Document Type



Virginia Institute of Marine Science

Publication Date



Journal of Shellfish Research





First Page


Last Page



Five species of invertebrates collected at bi-weekly to monthly intervals from an oyster reef in the James River, Virginia. between September 1984 and August 1985 exhibited similar patterns of fluctuation in abundance throughout most of the period. The species were: spat of the oyster Crassostrea virginica: two species that feed on oysters. the flatworm Stylochus ellipticus, and the gastropod Boonea impressa. as well as two others with no known direct trophic interactions with the oyster. the isopod Cassidinidea lunifrons and the nudibranch Doridella obscura. B. impressa was many times more abundant than S. ellipticus but because of the difference in feeding habits between the two species it is speculated that S. ellipticus has a greater harmful effect on oysters than its abundance would suggest. Densities of all species declined sharply between early October and early November; the decline was probably related to seasonal mortality associated with declining water temperatures. B. impressa and C. lunifrons were the most abundant species throughout most of the sampling period , but only oyster spat showed a definite high peak in recruitment in 1985. Failure of the data to show reproduction peaks for three of the other species was attributed to incomplete retention of smaller individuals in the 0.5 mm-mesh screen used: large variations in density did not permit clear definition of a peak in C. lunifrons. lt is recommended that studies of oysters on their reefs include other abundant noncommercial species to provide a stronger foundation for management of the resource than if only the oyster was studied.


seasonal abundance, Crassostrea, Stylochus, Boonea. Cassidinidea