EXCYSTMENT AND GROWTH OF CHRYSOPHYTES AND DINOFLAGELLATES AT LOW-TEMPERATURES AND HIGH SALINITIES IN ANTARCTIC SEA-ICE

Extreme environmental conditions have been thought to limit algal grow th in the upper sea-ice. In McMurdo Sound, Antarctica, chrysophyte sta tocysts (stomatocysts) and dinoflagellate hypnozygotes (resting cysts) overwinter in first-and second-year land-fast sea-ice exposed to temp eratures of -20 degrees C or lower. In early November, when temperatur es in the upper ice are <-8 degrees C and brine salinities are >126 ps u, dinoflagellate cysts activate and shortly thereafter excyst. During early November, chrysophyte statocysts also begin to excyst. Net dail y primary production occurs in the sea-ice brine at temperatures as lo w as -7.1 degrees C, at brine salinities as high as 129 psu, and at av erage photon flux densities as low as 5 mu mol photons.m(-2).s(-1). Di noflagellate densities were >10(6) vegetative cells.L-1 of ice while t emperatures in the upper ice were between -6.8 and -5.8 degrees C and brine salinities were similar to 100 psu. Chrysophyte densities reache d >10(6).L-1 of ice by early December. High densities of physiological ly active cryo- and halotolerant algae can occur in the upper land-fas t sea-ice under extreme conditions of temperature and salinity.