It is the purpose of this study to present a quantitative survey of the family Peridiniidae in Tomales Bay over the six month period between October thirtieth and May sixth. Emphasis has been placed on variation in the total Peridiniidae population for this period, on the seasonal variation of individual species, and on the possible effects of hydrographic and climatic conditions on the population.

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.

Very little is known of the development, life history, economic importance, of biological relationships of larval trematodes, especially in their molluscan and arthropod hosts on the Pacfic Coast. The comparatively few contributions to our knowledge have been from scattered and fragmentary observations. The purpose of this study was to expand our knowledge and to lay a foundation for further work on trematode life cycles in marine organisms. The area selected for special investigation was Nick's Cove, Tomales Bay, California.

Populations of the sympatric intertidal bivalves, Macoma secta and M. nasuta are compared as to reproductive ecology and population dynamics. Histological examination of seasonal gonadal changes indicate that both species undergo dormancy in the winter months and rapid gamete proliferation in the spring. However, the timing of spawning differs. The M. secta population synchronously spawned in August while the M. nasuta population spawned lightly in late spring and more heavily in the fall. Fecundity estimates indicate M. nasuta adds 140% of winter weight in gametes and M. secta only adds 43% of winter weight in gametes. Spat fall was detected in January for both species and was light in intensity, for either species only 24 per m2. Nursery areas were determined for M. nasuta, which corresponds to adult distributions, and for M. secta, which correspond to the upper and lower fringes of the intertidal distribution but not the center. Analysis of variance on distributional data indicate the temporal stability of density and size for M. secta. M. nasuta densities were also temporally stable but sizes were not. Both species demonstrated significant changes in density with tidal height. A measure of seasonal population variability, the Population-Time Mean Square, was found to have zero correlation with tidal height for M. secta, meaning that environmental stress was the same for individuals at each tidal height . This is believed related to the gradient of calm size to tidal height. An argument for density dependence in M. secta is given with emphasis on individual growth and realized population fecundity; the null hypothesis: As density increases, the resources per individual decrease, therefore the growth rate of individuals decreases. Analysis of sympatric populations indicate differing patterns of life history, pointing out that selection has favored these two species coexistence. Analysis of population dynamics indicated that in comparison to M. nasuta (Low Tide Horizon), M. secta (Mid Tide Horizon) was more stable (terminology from Ricketts, Calvin and Hedgpeth, 1969). This supports Castenholz’ (1967) idea that where climates are mild, the intertidal communities are more stable than the subtidal communities.

The objectives of the present study are to: (1) Describe the macro-invertebrate species composition and seasonal changes in abundance of the benthic infauna within an eelgrass bed; (2) Observe what immediate effects occur to the benthic community as a result of experimental removal of eelgrass plants from plants within the Zostera bed; (3) Measure the seasonal variation of eelgrass turion length over an annual cycle and determine its correlation to biomass (dry weight); (4) Examine, by means of field experiments, the importance of incident solar irradiation in affecting the seasonal growth of Zostera; and (5) Determine the relationship, if any, between the abundance of major invertebrate species and the abundance of eelgrass as determined by mean turion length.

These studies on the plankton of Tomales Bay were designed to determine the effects of such physical factors as tides, temperatures, salinities and sunshine on the quantities of various types of organisms, and to obtain a more comprehensive picture of estuarine life at the Pacific Marine Station. The studies were begun in the summer of 1948 and continued through the summer of 1953. Although various studies have been conducted on different aspects of marine plankton, the only general treatments of the subject of which the writer is aware are those of Johnstone (1924), Ricketts and Calvin (1951), Sproaton (1949) and Sverdup (19461). It is hoped that these additional studies will be of general interest to biologists and that they may form the basis for the solution of some of the many intriguing problems which have been encountered and are here presented in graphic form.

The study of fish diets or feeding behavior is an important aspect in ecology. Analysis of fish stomach contents often provides data for determining resource utilization, feeding strategies, and overlaps in food items among and between species. Studies of fish diets could also be used for testing ecological theory or provide management procedures for fisheries if methods could be developed for minimizing competitive food utilizations by other fish and enhancing growth of exloited fish populations (Obrebski and Sibert 1977). In order to understand more about ecological communities and competitive predatory relationships of fish, more data are required on their diets and feeding habits (Pearcy and Hancock; 1973). Detailed accounts of prey items consumed by some flatfish in the northwest Pacific are by Hagerman (1952), Kravitz et al. (1977), and Pearcy and Hancock (1978). This study examines the diet and growth of two juvenile flatfish, the English sole, Parophrys vetulus (Girard 1854) , and the Speckled sanddab, Citharichthys stiamaeus (Jordan and Gilbert 1832). In the present study the English sole and Speckled sanddab are investigated in order to determine their growth and seasonal changes in their diets, switching of food items, and overlaps of diet items between species and among size groups within species.

Tomales Bay is situated in Marin County, about 40 miles north-west of San Francisco. This shallow bay averages about 1.5 miles in width and is about 12.6 miles in length, with an average depth of 12 feet (Johnson, Bryant and Hedgpeth, 1961). Oyster and herring comprise the main fishing industry, although the bay contributes a great amount of perch, smelt, halibut, and shark. Gill and seine nets are the most common gear used by fishermen. The primary objectives of this study were: (1) to determine the species composition of the bay, and the relation between seining success at different localities and such factors as tides and temperature; (2) to describe the life history of Phanerodon furcatus Girard, the most common perch of the bay.