Analyses of the benthic community structure of a mudflat in South San Francisco Bay over a 29-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinal clam Macoma balthica from the same area. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that could be indicative of a more stable community that is subjected to less stress. In addition, two of the opportunistic species (Ampelisca abdita and Streblospio benedicti) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals. Heteromastus filiformis, a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying their eggs on or in the sediment has shown a concurrent increase in dominance. These changes in species dominance reflect a change in the community from one dominated by surface dwelling, brooding species to one with species with varying life history characteristics. Analysis of the reproductive activity of Macoma balthica shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissue of this organism. Reproductive activity is presently stable with almost all animals reproducing during the two reproductive seasons (spring and fall) of most years. These findings are consistent with findings previously reported for the 1974 through 2002 period.
ABSTRACT 5
INTRODUCTION 6
Previous monitoring of the benthic community in the near field receiving waters 6
Approach 7
Objectives 8
Study Site 8
Methods 8
Laboratory Analysis 8
Results and Discussion 9
Reproduction of Macoma balthica 9
Benthic Community 9
Value of Long Term Monitoring 10
References 11
Figures 13
Appendix A: Palo Alto Macoma balthica Reproduction Excel File (26KB)
Appendix B: Palo Alto Benthic Community Excel File (17KB)
This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.
Download the report (PDF, 595KB)
Document Accessibility: Adobe Systems Incorporated has information about PDFs and the visually impaired. This information provides tools to help make PDF files accessible. These tools convert Adobe PDF documents into HTML or ASCII text, which then can be read by a number of common screen-reading programs that synthesize text as audible speech. In addition, an accessible version of Acrobat Reader 5.0 for Windows (English only), which contains support for screen readers, is available. These tools and the accessible reader may be obtained free from Adobe at Adobe Access.
For more information about USGS activities in California, visit the USGS California District home page.
| AccessibilityFOIAPrivacyPolicies and Notices | |
  |
|