U.S. GEOLOGICAL SURVEY
Open-File Report 03-224
ABSTRACT
Analyses of the benthic community structure over a 28-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 2000
period
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Link to Appendix 1 Palo
Alto Benthic Community (Excel File, 0.42 MB)
Link to Appendix 2 Palo Alto Macoma balthica Reproduction (Excel File, 0.17 MB)
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Send questions or comments about this report to Janet K. Thompson (jthompso@usgs.gov) (650) 329-4364
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