Abstract

Saline-lake ecosystems, when examined over a wide range of salinities, show an inverse relation between salinity and number of species present. However, when the salinity range is narrow the correlation disappears, but the abundance of individuals within a species may change significantly in response to small changes in salinity. These concepts were evaluated within wide and narrow salinity ranges in Great Salt Lake. The construction of a solid-fill railroad causeway across Great Salt Lake in 1959 divided the lake into two separate bays of differing salinities. Virtually all the surface water discharging into the lake enters the south bay (Gilbert Bay); the north bay (Gunnison Bay) receives only precipitation and a small amount of flow from Gilbert Bay through several culverts. Because these differences resulted in increased salinity in Gunnison Bay relative to Gilbert Bay, separate aquatic ecosystems have developed. Precipitation and subsequent runoff from 1959 to 1963 was small causing record low lake elevation and high salinity. Gunnison Bay was dominated by only 6 species and about 15 species may have been present in Gilbert Bay. Record high runoff during 1982-87 resulted in large dilution of the brine and significant changes in the ecosystems of both bays, particularly Gilbert Bay where 32 species were present by 1987. Annual changes in runoff volume generally result in small changes in salinity and in the species composition in both bays but may greatly alter the abundance of individual species. Successive annual declines in salinity of about 2 percent in Gilbert Bay from 1995 to 1997 altered the phytoplankton community and resulted in a relatively large decline in shrimp productivity in 1997. In general, higher salinity restricts the lake ecosystem to fewer tolerant organisms in both bays. Lower salinity allows greater diversity in the biota, but cumulative small changes in salinity may decrease the productivity of the ecosystem.