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WILDLIFE BOTTOM DWELLERS CONTEXT The tiny creatures living at the Good bottom of the Estuary will never be seen by most people, yet these filter and deposit feed- ers can affect the entire food web. When eco- systems lose native benthic diversity, they can DELTA 100% less productive, less resilient in the face of be 80 stresses, and provide fewer ecological services. The benthic community is a key part of estuary 60 food web dynamics and nutrient cycling, and a 40 classic bio-indicator of estuary health. Benthic 20 invertebrates are more localized indicators of 0 estuary health than plankton or fish. They are sufficiently sensitive and have short enough life cycles that changes in benthic community patterns can indicate large recent changes in nutrient loading, toxic substances, or sedimenta- CONFLUENCE 100% patterns. tion Fair Poor 2013 2009 2005 2001 1997 1993 1989 1985 1981 Good 100% DELTA INDICATOR This indicator analyzes benthic Fair 60 80 2013 2009 2005 2001 1997 1993 1989 1985 1981 0 trends for the various benthic indicators vary and are not entirely positive. While native diversity has remained good compared with 1981-86 historical levels, a large proportion of Poor 2013 2009 2005 2001 1997 1993 1989 1985 1981 DETAILS STATUS & TRENDS The status and Fair Poor community composition and native species 60 40 diversity in the upper Estuary at three sites with 40 20 long sampling records (1981-2013). Scientists ana- 20 lyzed the three sites independently because of 0 Good 80 the large differences in benthic communities between regions. The data analyzed for the indi- cators comes from benthic grab samples, which have been collected, identified to species, and counted in the same way for the whole period of the monitoring program. The benchmark is based on the historical period of 1981-86: 1981 was the earliest year-round monitoring at all sites, and the 1986-87 invasion of the Asian overbite clam (Potamocorbula amurensis), along with several other non-native species, marked a drastic community shift at two of the study sites. Current (2009-2013) native diversity that was equal to or higher than the historical average was counted as good. For community com- position, good was set at or above 75% native. Trends for all three sites were evaluated by determining whether the current status differed significantly from the historical benchmarks. COMMUNITY COMPOSITION BY INDIVIDUAL P E R C E N T N AT I V E I N D I V I D UA L S SUISUN 100% 80 60 20 20 0 2013 2009 2005 2001 1997 1993 1989 1985 1981 2013 2009 2005 2001 1997 1993 1989 1985 1981 2013 2009 2005 2001 1997 1993 1989 1985 1981 0 Poor 40 Poor Poor 40 DELTA Fair 40 –use only indicator 20 3 – Ds with location names 0 7, confluence 4, delta 28 60 Fair Fair 60 80 CONFLUENCE Good 80 100% Good Good 100% BOTTOM DWELLERS 41 N AT I V E B E N T H I C the community’s I N V E R T E B R A T E S species and individuals are S U I S U N B AY & D E LTA now non-natives at some sites. . . S TAT U S . . This is especially Fair true at one site . . . .T R E N D . . . . in Suisun Bay, Mixed a major site of .....BENCHMARK..... Potamocorbu- Diversity level 1981-1986 la amurensis Community composition % native invasion. At this site, over the last five years, native species were 50% of the species diversity but native individuals were only 5% of the total count. The current community composition was consider- ably better at the confluence of the Sacramento and San Joaquin Rivers, where 74% of species and 74% of individuals were native. Community composition was also better in the Delta, where 88% of species and 67% of individuals were native. THREATS & CHALLENGES The patterns seen among benthic invertebrate indicators are a clear indication the benthic communities of the Estuary and Delta are not in a pristine state and are unlikely to return to their original composition. The Estuary remains one of the most invaded in the world. It is not clear exactly how the current benthic community functions differently from the historical one: many of the non-native species were introduced long before regular monitoring. While it is heartening that there has been no large net loss of native diversity at the species level, management of species such as salmonids and smelt should take into account the potential changes in benthic-pelagic food web interaction.