Date Awarded

1973

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Virginia Institute of Marine Science

Advisor

Marvin Wass

Committee Member

Michael E. Bender

Committee Member

Dexter S. Haven

Committee Member

Joseph G. Loesch

Committee Member

Clinton E. Parker

Abstract

This project investigated several aspects of the autecology of the brackish water clam Rangia cuneata in the James River, Virginia. The study, conducted from August, 1970, through March, 1972, was primarily concerned with substrate and salinity effects on growth and condition index of R. cuneata. The studies were conducted in sand and mud substrates in four different salinity regimes. Monthly samples of 15 clams were collected at each of the eight stations for condition index determinations. Condition index was shown to vary seasonally, with a low point in early spring and a maximum in early fall. Values were higher in sand bottoms than in mud and decreased in both substrates in fresher water. Clams from sand bottoms showed a pronounced fall peak which was not evident at most mud stations. A field experiment to evaluate the relative importance of water associated and sediment-associated factors in determining condition index showed that some factor associated with the water pumped by the clams was most important. The hypothesis is presented that this factor may be related to the large difference in suspended solids taken in by clams in sand and mud bottoms. Growth studies were based on marked individuals planted at all eight stations and recovered after one year. Growth was measured in terms of shell length and live weight increases. In terms of both criteria, growth was greatest at the three downriver sand stations. The lowest salinity sand station showed considerably less growth, but exceeded the growth at all mud stations. Clams at the latter showed similar small increases in both length and weight. The above patterns of condition index and growth are discussed in relation to salinity structure and suspended solids in the environment and to osmotic stress and spawning activity of the clams. An explanation is offered for the large size and relatively high condition index of clams near their limit of penetration into fresh water. The potential commercial value and annual harvest of R. cuneata in the lower James River is estimated. This dissertation is from the Joint Program Degree from the College of William & Mary and University of Virginia and awarded by the University of Virginia.

DOI

https://doi.org/10.25773/eptx-n781

Rights

© The Author

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