Date of Award


Document Type


Degree Name

Master of Science (M.S.)


Biological Sciences

First Advisor

Steven Obrebski

First Committee Member

James A. Blake

Second Committee Member

Edmund H. Smith


The changes in population density, growth and biomass of two infaunal, sympatric, suspension-feeding bivalves, Musculus senhousia (Benson, 1842) and Protothaca staminea (Conrad, 1837), have been investigated over an eighteen month period in Tomales Bay, California. M. senhousia, a mussel, displays two basic spawning times, one of which occurs in late spring, while the second spawning takes place in late summer. M. staminea, a venerid, spawns once during late spring. The population density of the mussel ranged from 9,180 m-2 in early spring to 752 m-2 in the fall of 1976. M. staminea had a maximum density of 1,120 m- 2 in the summer, and the minimum of 265 m- 2 coincided with winter. The growth of M. senhousia appears to take place primarily during the spring and summer months, while that of P. staminea occurs in late winter and summer, with a slight recession during the spawning period. The Bertalanffy growth equation was applied to both species and it was found that M. senhousia grows to a shell length of approximately 25 mm in 10 to 11 years; whereas, ~ staminea reaches Q shell height of 37 mm in 15 to 16 years. There was a large seasonal variation in biomass of both species with the greatest difference occurring between winter and spring for the mussel, while that of the venerid took place immediately before and after spawning. Not only were the older age groups better represented in the population of M. senhousia, but also the smaller sizes both experienced higher mortality and tended to predominate in the upper intertidal areas. The densest population of both species occurred between the tidal heights of 1.10 m to .28 m, which occupies the middle lntertidal zone (MLW). The sediment in these areas ranged from coarse to medium sand.



Included in

Biology Commons



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