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The Delta Smelt Hypomesus transpacificus is a small translucent fish that lives in the heart of California's water distribution system. It is an endemic species that is on verge of extinction, largely because it is in direct competition with people for water. This article discusses the controversy surrounding this fish by describing (1) the biology of Delta Smelt; (2) California's complex water storage and distribution system; (3) the history of Delta Smelt, including conservation efforts; (4) the present controversies surrounding it; and (5) the future of Delta Smelt. The decline of Delta Smelt is a strong indicator that the ecosystem of the Sacramento–San Joaquin Delta has undergone large‐scale changes that make it an unfavorable environment for native fishes. Reversing the trajectory of the Delta Smelt toward extinction will require major shifts in California water policy and water use as well as active management of the smelt's habitat and life history. [ABSTRACT FROM AUTHOR]

Selenium uptake from food (assimilation efficiency) and dissolved phase (influx rate) as well as loss kinetics (efflux rate) were compared between two bivalves, Corbicula fluminea and Potamocorbula amurensis. The effects of salinity and temperature on these kinetic parameters for both clam species also were evaluated. The Asiatic clam, C. fluminea, more efficiently assimilated Se associated with algae (66-87%) than Se associated with oxic sediments (20-37%). However, no consistent difference was found between Se assimilation efficiencies from both food types (19-60%) for P. amurensis. The temperature and salinity had a minor influence on the Se assimilation from ingested food. However, the effects of temperature and salinity were more evident in the uptake from dissolved sources. The influx rate of Se(IV) increased by threefold with the increase of temperature from 5 to 21°C for C. fluminea. The increase of salinity from 4 to 20 psu decreased the uptake rate constant (ku) of Se in P. amurensis from 0.011 to 0.005 L/g/h, whereas salinity change (0-8 psu) had a negligible effect on the Se influx rate of C. fluminea. The Se influx rate of P. amurensis decreased by half with the 3.5-fold increase in tissue dry weight. The rate constant of loss was greater for P. amurensis (0.029/d at 8 psu) than for C. fluminea (0.014/d at 0 psu and 0.01/d at 8 psu). A bioenergetic model suggests that dietary uptake is the dominant pathway for Se bioaccumulation in the two clams in San Francisco Bay and that interspecies differences in Se bioaccumulation can be explained by differences in food ingestion rates. [ABSTRACT FROM AUTHOR]

Silica distributions in estuaries can be used to infer uptake, particularly that due to production by diatoms. I used data from two long-term monitoring programs to infer long-term patterns of diatom production during summer in the river-dominated northern San Francisco estuary. This region was most heavily affected by grazing by the clam Potamocorbula amurensis, introduced in 1986. Production based on dissolved silica (Dsi) uptake was high during the 1970s and early 1980s except during a drought in 1976-1977. From 1987 to 2002 production averaged 1% and 17% of the preclam values from the two monitoring programs. Low values in 1976-1977 and after 1986 are consistent with a loss of diatom production due to benthic grazing. There is no evidence of a relation between Dsi-based production and either freshwater flow or temperature, and therefore climate change is an unlikely influence on the long-term trend in diatom production in this part of the estuary. Primary production calculated from chlorophyll and extinction coefficient was of a similar magnitude to that calculated from DSi depletion, indicating that most production was due to diatoms during summers of the preclam period. [ABSTRACT FROM AUTHOR]

The article presents the study that shows the relative effects of the invasion of Asian clam, Potamocorbula amurensis, on foraging species of diving ducks in San Francisco Bay, California. The topics discussed include the effects of exotic invertebrate invasions on aquatic communities, the tremendous rise of the clam species as compared to the rays, sharks, flatfish, crabs and diving duck species in the area, and the effects of food base alteration on the scaup ducks population.

Respiration and calcium carbonate production by the invasive Asian clam, Potamocorbula amurensis, were calculated to assess their importance as CO[sub2] sources in northern San Francisco Bay. Production, calculated using monthly population density and size structure measured at three sites over 7 yr and a shell length/CaCO[sub3] conversion factor, averaged 221 (± 184) g CaCO[sub3] m[sup-2] yr[sup-1]. Net calcium carbonate production by this exotic bivalve releases CO[sub2] at a mean rate of 18 (± 17) g C m[sup-2] yr[sup-1]. Respiration by P. amurensis, estimated from secondary production, releases additional CO[sub2] at a mean rate of 37 (± 34) g C m[sup-2] yr[sup-1]. Therefore, total net CO[sub2] production by P. amurensis averages 55 (± 51) g C m[sup-2] yr[sup-1] in an estuarine domain where net primary production consumes only 20 g inorganic C m[sup-2] yr[sup-1]. CO[sub2] production by P. amurensis in northern San Francisco Bay is an underestimate of the total CO[sub2] supply from the calcified zoobenthic communities of San Francisco Bay, and results from other studies have suggested that this rate is not unusual for temperate estuaries. Global extrapolation yields a gross CO[sub2] production rate in the world's estuaries of 1 x 10[sup14] g C yr[sup-1], which suggests that calcified benthic organisms in estuaries generate CO[sub2] equal in magnitude to the CO[sub2] emissions from the world's lakes or from planetary volcanism (the net source is determined by the highly variable rate of CO[sub2] consumption by carbonate dissolution). This biogenic CO[sub2] source is increasing because of the continuing global translocation of mollusks and their successful colonization of new habitats. [ABSTRACT FROM AUTHOR]