were toxic. Collectively, these chemical, toxicity and benthic community data suggest that 

 some unquantified factor(s) that co-occurred with these fine-grained, organically enriched 

 sediments somehow induced or influenced the biological responses. The data from Tomales 

 Bay corroborate the strength of using multiple indicators such as those included in the 

 Sediment Quality Triad concept (Long and Chapman, 1985; Chapman et al., 1987) in 

 environmental assessments, since the chemical data, if collected alone, would have not 

 suggested that biological effects were likely. However, both the toxicity tests and benthic 

 community data demonstrated that the sediments were relatively inhospitable due to some 

 unknown factor(s). 



Benthic Community Composition. 



The benthic community composition differed significantly among the four sites for which 

 data are available. All parameters measured or calculated indicated between-site 

 differences. Similarity in composition among stations at each of the four sites was relatively 

 high. However, the degree of chemical contamination at these four sites did not differ 

 remarkably, whereas it was relatively high at the OA site as compared to these four. 

 Because no benthic data are available thus far for the most contaminated site, it is not 

 possible to attribute the observed faunal differences in the benthos among sites to chemical 

 contamination. Nichols (1979) summarized some of the natural factors that may contribute to 

 alterations among benthic communities along with or instead of toxic chemicals in San 

 Francisco Bay. The between-site differences in benthos observed at the four sites may be 

 attributable to "natural" factors as well as the small differences in chemical contamination. 

 The observation of relatively low abundance of crustaceans at the apparently least 

 contaminated site, along with the indication of toxicity of sediments from that site to 

 amphipods, mussel larvae, and urchin larvae suggest that some unquantified factor or 

 characteristic of the TB sediments was toxic to sensitive species. Taxonomic analyses of the 

 benthos from the OA site—where toxicity and contamination were generally highest— will 

 confirm (or refute) the speculation that the benthos there were most affected by pollutants. 



In conclusion, the composition of benthic communities differed significantly among sites. 

 This type of analysis is a tool that has been used in many studies of water quality in San 

 Francisco Bay and many other places. The analyses are ecologically relevant, since the 

 organisms are residents, form a major component of the ecosystem, and constitute an in situ 

 bioassay of sediment quality. However, the composition of benthic communities is influenced 

 and controlled by many natural factors such as proximity to brood stock, bottom scouring, 

 water temperature and salinity, predation, depth, and sediment texture. Many of these 

 factors probably varied among the sampling sites. Therefore, the differences in composition 

 among the four sites could not be attributed only to the presence of chemical contamination. 



Sediment Profiling Photography 



The survey of 69 sites with sediment profiling photography provided useful baseline 

 information on sedimentological characteristics of the estuary. The data indicated that the 

 majority of the estuary was not organically enriched. However, some indices of sediment 

 quality developed in the survey of 69 sites indicated poor conditions in selected peripheral 

 harbors and channels. Among the four sites that corresponded with those sampled for 

 measures of toxicity/contamination/benthos, the sediment profiling photography indicated 

 that the OA site was most modified by sewage and organic enrichment. However, these data 

 indicated that the infauna at that site were only minimally stressed. This survey technique 

 has been used in studies of many fjords and estuaries worldwide, especially regarding re- 

 colonization of defaunated sediments or organic enrichment of sediments. In conclusion, 

 sediment profiling photography has been shown in numerous studies, including this one, to 

 provide useful information on sedimentological and biological properties of soft-bottom 

 sediments very quickly. 



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