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PROCESSES Zooplankton sample preserved in quart jar with 10% formalin and Rose Bengal dye added. Photo: California Department of Fish & Wildlife particularly in the low salinity zone. Biologists attribute this decrease in large part to the 1986 invasion of the zone by the clam P. amurensis. Competition with P. amurensis for phytoplank- ton, a shared food resource, as well as clam consumption of copepod nauplii (babies) may have reduced zooplankton. Mysid biomass has declined in both the Suisun and Delta regions since monitoring began. The 2010-2014 average biomass was 1.6 milligrams of carbon per cubic meter of water sampled from Suisun and 0.4 milligrams from the Delta. There was a significant downward trend in annual mysid biomass for both re- gions from 1974-2014. Although mysid biomass is lower than it was historically, it does not appear to be declining further. In the Suisun region, calanoid copepod biomass has declined since monitoring began, with small peaks occurring during higher flow years such as 2006 and 2011. Like the mysids, there was a significant downward trend from 1974-2014 in the Suisun region. Also like mysids, biomass is lower than it was historically, but it does not appear to be declining further. In the Delta region, there was a significant increase in calanoid copepod biomass from 1974- 2014, but little change in the last 14 years of that period. For trends in the second indi- cator, abundance of fishes in the pelagic and marsh (Suisun) zones has decreased substan- tially since the early 1980s. Fish abundances in the marsh and pelagic zones of the upper Estuary that appeared to increase in the mid- 1990s have resumed declining since the early 2000s. Abundance of fish in the third habitat examined, the Delta beach zone, has increased in recent years. Some of this change is attribut- able to increases in non-native fish populations in this habitat zone. THREATS & CHALLENGES The food web of the upper San Francisco Estuary has been highly altered by the long term diversion of freshwater inflows, as well as by the introduction of non-native species, including the clam P. amurensis, water weeds such as Egeria, 71 FOOD ZOOPLANKTON AS FOOD S U I S U N B AY & D E LTA . . S TAT U S . . Fair . . . .T R E N D . . . . Mixed .....BENCHMARK..... Average biomass 1974-1986 FISH AS FOOD S U I S U N B AY & D E LTA . . S TAT U S . . Fair . . . .T R E N D . . . . Deteriorating .....BENCHMARK..... Historical Average 1980-1989 1995-2004 (Delta Beach)