GAMMARIDAE Latreille, 1802

Graening, G. O., Rogers, D. Christopher, Holsinger, John R., Barr, Cheryl & Bottorff, Richard, 2012, Checklist of Inland Aquatic Amphipoda (Crustacea: Malacostraca) of California, Zootaxa 3544, pp. 1-27 : 16

GAMMARIDAE Latreille, 1802

Gammarus daiberi Bousfield, 1969 (euryhaline, exotic)

Records: Found in dredge samples collected in Contra Costa, Sacramento, San Joaquin, and Solano Counties at San Pablo Bay, Grizzly Bay, Suisun Bay, Sherman Lake, Frank’s Tract, Sacramento R., Old R., Mandeville Tip, Brown's Island, and Mildred Island, San Joaquin R., and West Canal at Clifton Court Forebay intake ( Toft 2000; CDWR database).

Comments: Introduced into the Delta probably from ballast water discharging ( Cohen and Carlton 1998, Toft 2000, Toft et al. 2002, Chapman 2007).

Gammarus lacustris sensu lato Sars, 1864 (stenohaline)

Records: Inyo Co. “ Lakes of Owens R. drainage basin (Mildred L., etc.), Bishop, N. Reimers coll., 1954 ” ( Bousfield 1958); Owens R. at Hwy 136 (Usjak, in manuscript). Kern Co. Railroad Spring (Usjak, in manuscript). Lassen Co. Eagle Lake at Spaulding Rocks , 22 specimens, 22 May 1987, D.C. Rogers; Eagle Lake , trout stomach contents, taken off Gallatin Beach , 19 Aug. 1994, D.C. Rogers; Cleghorn Reservoir , 20 Aug. 1994, D.C. Rogers; Grasshopper Valley , unnamed spring at south end, 26 Apr. 1998, D.C. Rogers. Mono Co. Mono Lake in Dechambeau Cr. ( Usjak , in manuscript). Solano Co. South of Suisun City , Hill Slough, in freshwater pools above Salicornia marsh, 2 Apr. 1994, D.C. Rogers .

Comments: Gammarus lacustris is reported from cold lakes, tundra ponds, sloughs, etc., of midwestern and western USA, Canada, Alaska, northwestern Europe, and Asia ( Bousfield 1958, Holsinger 1972, Barnard and Barnard 1983, Hou et al. 2007). This holarctic taxon undoubtedly consists of several species ( Barnard and Barnard 1983, Chapman 2007). G. lacustris was introduced to Lake Tahoe (Franz and Cordone 1966) and the Salton Sea ( Barnard and Barnard 1983), but neither population established.

Gammarus mucronatus (Say, 1918) (euryhaline, exotic)

Records & Comments: Native to North American Atlantic coastal waters, this species was introduced to the Salton Sea probably in 1957 when the marine grass Diplanthera from Texas was intentionally introduced ( Barnard and Gray 1968). Simpson et al. (1998) reported that, “ in the absence of fish Gammarus mucronatus dominated the benthos at the lower salinities.”, but they also predicted that, “ Gammarus will disappear from the Salton Sea as the salinity increases.”