U.S. GEOLOGICAL SURVEY
Open-File Report 02-394
Analyses of the benthic community structure over a 26-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.
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Link to Appendix 1 Palo Alto Benthic Community (Excel File, 0.26 MB)
Link to Appendix 2 Palo Alto Macoma balthica Reproduction (Excel File, 0.04 MB)
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