Polychaetes are important components of the intertidal sandflat community in Lawson’s Flat, Dillon Beach, California. Little is known about the factors that control the relative abundance of these species. In view of the extensive evidence of the importance of interactions between component species in intertidal communities it is of interest to obtain information that would facilitate future experimental work of such interactions. This study documents seasonal changes in the abundance of the polychaete component of the intertidal community. Attention is directed at possible factors that might affect seasonal changes in distribution. A major finding is that certain herbivorous polychaetes exhibit seasonal fluctuations in abundance that appear to be correlated with changes in algal cover. These findings might suggest more detailed future experimentation. Some aspects of recruitment of major species are considered and the presence of a parasite in one of the species is noted. Aspects of benthic community ecology are discussed.

This thesis represents a zooplankton study of Tomales Bay, Marin County, California. It consists of two papers. The first paper, "The Abundance of Copepods in Tomales Bay, California" has been submitted to the California Fish and Game for publication. The second paper, "Diet Studies of the Ctenophore Pleurobrachia bachei has been submitted to Fishery Bulletin. The raw data has been compiled in the Appendix.

Pododesmus cepio Gray (1850), a bivalve mollusk of Family Anomiidae, is native to the Pacific coast of North America and common in Tomales Bay, California. A small population of the European oyster, Ostrea edulis Linnaeus (1758), is being raised experimentally at the Tomales Bay Oyster Company. The histological study of the seasonal gonadal changes of these two species, in Tomales Bay, is described below. The study of gametogenesis in O. edulis in Tomales Bay is desired to evaluate the reproductive adaptation of this animal to a new set of ecological conditions. The inclusion of the native P. cepio in this study allows comparison of the gonadal development of these two species. Such a comparison aids not only in understanding the seasonal gonadal changes in both species, but also in examining the adjustment of the introduced form, O. edulis, to a new environment.

It is hypothesized that difference between containers and between sediments will produce structural differences in the resulting communities by intensifying competition for resources, and by excluding certain classes of predators. It is also hypothesized that the level of the effect of container, substrate, and time on community structures will be dependent on tidal level. Paine (1969) and Dayton (1972) have demonstrated that the structure of some communities is largely determined by the effects of foundation, or keystone, species. It is suggested that the structure of classic-substrate communities may be determined similarly.

The purpose of this study is to describe the sediment-dwelling, infaunal gammaridean amphipods of Tomales Bay and to relate their distribution to known variations in the physical environment. Also, the Tomales Bay amphipod fauna is compared to the faunas of other West Coast bays.

Confronted with a diverse sandflat community of interacting organisms and a spectrum of physical forces, a meaningful community analysis should begin with a description of physical characteristics and faunal distributions over time. The functional importance of certain species in the community should then be investigated by using both field and laboratory experiments. Consequently, the purpose of this research was twofold: (1) to apply the methods of similarity and gradient analysis to describe the faunal gradation on an intertidal sandflat and; (2) use these data to design a predator exclusion field experiment aimed at assessing the effects of shorebird, crab and fish predation on certain infaunal and epifaunal invertebrates.

Thesis (Ph.D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves 161-169). / Microfiche. / xii, 169 leaves, bound ill., maps 29 cm

The Bat Ray, Myliobatis californica Gill, occurs from Oregon to the Gulf of California and is common in California bays during the spring and summer. MacGinitie (1935) observed that during its feeding activities, the Bat Ray can dig channels up to 1 meter wide, 50 cm deep and 4.5 meters long in benthic substrates. In intertidal sand flats in Tomales Bay, California, circular pits up to 1 meter in diameter and 20 cm in depth are made by Bat Rays in late summer. In some areas over 50% of the sand flat surface is covered with Bat Ray pits. This recurrent seasonal disturbance of the substrate due to Bat Ray predation on benthic communities may be important in affecting their structure and faunistic composition. In preliminary studies of the effects of predation on benthic communities in Tomales Bay, we were interested in obtaining information about changes in diets of Bat Rays in relation to size.

Two species of oviparous oysters, Crassostrea virginica (Gmelin, 1790), the Eastern oyster, and Crassostrea gigas (Thunbert, 1793), the Japanese oyster, were introduced into Tomales Bay, California, for commercial purposes. Because these oysters do not propagate in Tomales Bay, new shipments of adult oysters or oyster spat must be periodically sent from the east coast of the United States or from Japan. It is the purpose of this study to compare the seasonal gonadal changes which occur in the two species of adult oysters in Tomales Bay with one another, and to compare them with the seasonal gonadal changes which occur in the same species of oysters in other regions. The differences in gonadal changes will be related to variances in environmental conditions and to specific or racial characteristics. The introduction of oysters into a new environment is valuable for both commercial and scientific reasons. Although it has long been known that C. virginica and C. gigas do not propagate in Tomales Bay, no one has ever done a detailed study of their reproductive cycle or the seasonal histological changes in their gonads. This study, therefore, extends the knowledge concerning an oyster's reaction and adaptation to its new environment.

This report summarizes the results of a study on the life cycle of a member of the trematode family Acanthooolpidae, genus Stephanostomum Looss, 1899, which was carried on during the summers of 1948, 1949, 1951, and the winter of 1948-49 at the Marine Station of the College or the Pacific at Dillon Beach, California. Only one previous experimental work has been done on the life cycle of any member of this family. Martin (1939) reported the life cycle of Stephanostomum tenue (Linton) which he had obtained at Woods Hole, Massachusetts. Modifications of his technical procedures have been used in this study. It is hoped that this endeavor will further facilitate investigations in life cycle studies. The results obtained may be of economic value because the adult members of the family are parasitic in marine fishes, many of which are of commercial importance.