Distribution and Abundance of Planktonic Crustacea in Sturgeon Bay and Shawanaga Inlet, Georgian Bay, Ontario

Abstract

Distribution and abundance of 27 planktonic crustaceans in an inshore area of Georgian Bay characterized by horizontal differences in temperature and electrolyte concentrations are described on the basis of duplicate vertical hauls on eight dates at six stations during ice-free months of 1970 and on one date at four stations through the ice in 1971. Most species were found at all stations on at least some occasions in 1970, although some differences in periods of maximum abundance between stations, probably related to temperature, were noted. Daphnia ambigua and Diaptomus reighardi were confined to the inner stations. Limnocalanus macrurus and Diaptomus sicilis were absent during periods of highest water temperatures. Eubosmina coregoni, although found throughout the system in February 1971, was restricted to the outer stations in 1970. A marked late-summer drop in populations of all species except Bosmina longirostris and Tropocyclops prasinus mexicanus in 1970 might have been due to either normal seasonal fluctuations or heavy predation by planktivorous fish.