THE ENVIRONMENTAL TOLERANCES AND BEHAVIORAL ECOLOGY OF THE SUB-ANTARCTIC BEACH-HOPPER ORCHESTIA-SCUTIGERULA DANA (CRUSTACEA, AMPHIPODA) FROM HUSVIK, SOUTH GEORGIA

''Orchestia'' scutigerula Dana (Amphipoda: Talitridae) was found benea th supralittoral stones at Kanin Point, S. Georgia, Microhabitat tempe ratures recorded over 6 summer weeks varied widely (hourly, diurnally, weekly), especially under stones highest upshore. In air, ''O.'' scut igerula tolerated temperatures between -2 and 19 degrees C. Temperatur es between 19 and 28 degrees C were survivable only in fully saturated air. In water, a temperature of 19 degrees C was tolerated for 6 h. T he locomotory behaviour (walking) of amphipods for 3 h underwater was the same in distilled water as seawater. After 6 h in distilled water, amphipods exhibited distress, and after 7 h most were incapable of wa lking. ''0.'' scutigerula is a strong hyper/hypo-osmoregulator during short-term exposure to a wide range of salinities. All individuals tes ted survived any combination of salinity and temperature between 5 and 34 parts per thousand and 2 and 12 degrees C. Amphipods chose, (a) sh aded conditions both in air or in water, (b) moist to dry gravel, and (c) moist gravel to moist sand. They did not burrow into moist sand, e ven though markedly thigmokinetic. In uniform, featureless containers amphipods were quiescent during the day, clumping together. At night s uch clumps dispersed and exploratory activity increased. Swimming was never observed, and when out of water these talitrids hopped rarely. T ussock grass and macroalgal debris dominated their gut contents in sit u, with terrestrial plant debris increasing in prominence in amphipods from higher upshore. Feeding trials revealed high consumption of rott ing tussock grass debris and green algae (Ulothrix, Ulva). Soft materi als were consumed preferentially. Rate of passage of food through the gut was very variable, both within and between individuals. Underwater , ''O.'' scutigerula fed at half the rate in air. Food preferences of individuals sometimes switched between equally available foods over ti me, Fecundity is linearly related to female body length. Eggs more tha n double in volume during development.