Thesis

Ecological aspects of protothaca staminea (Conrad,1837) (Bivalvia:Veneridae)

A study was made of Protothaca staminea in the Mugu Lagoon, California. Two areas were studied: a sandy channel and a muddy sand backwater. Random sampling of the two areas was done to determine the relative densities and dispersions of P.staminea. The organisms were measured for length, height, width, and age. "Size" was determined as a composite of length, height, and width. Age was determined by the presence of annual rings. The amount of growth in each ring was measured in order to compare yearly growths of bivalves in each area. Sediments were analyzed for particle size, e.g.,silt and clay, fine sand, etc. Bivalves were also taken from the Venice Canal and from Tomales Bay, California for the purpose of comparison. The density of Protothaca s taminea in the muddy sand was three times that in the sandy channel. In both areas the' showed contagious distributions. Student's t-tests showed significant differences in first year growth among all four of the areas. Differences in other years were reflected by their mean values although not all these differences were statistically significant. Within any one year class, significant seasonal differences were seen in growth. The sediment in the two Mugu Lagoon areas was shown to be dependent upon current velocity. Great current velocity inhibits growth in young Protothaca staminea, but moderate current increases growth rate. Current flow is the factor responsible for the weak associations between growth as a function of "size" and certain sediment components in a multivariate correlation analysis. Age, an index of survival, was correlated to certain sediment sizes also. Food availability, defined as plankton or, in one instance, possibly organic detritus,caused this correlation.

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