The environmental tolerances and behavioural ecology of the sub-Antarctic beach-hopper “Orchestia” scutigerula Dana (Crustacea: Amphipoda) from Husvik, South Georgia

“Orchestia” scutigerula Dana (Amphipoda: Talitridae) was found beneath supralittoral stones at Kanin Point, S. Georgia. Microhabitat temperatures recorded over 6 summer weeks varied widely (hourly, diurnally, weekly), especially under stones highest upshore. In air, “O.” scutigerula tolerated temperatures between −2 and 19 °C. Temperatures between 19 and 28 °C were survivable only in fully saturated air. In water, a temperature of 19 °C was tolerated for 6 h. The 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 walking. “O.” scutigerula is a strong hyper/hypo-osmoregulator during short-term exposure to a wide range of salinities. All individuals tested survived any combination of salinity and temperature between 5 and 34‰ and 2 and 12 °C. Amphipods chose, (a) shaded 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, even though markedly thigmokinetic. In uniform, featureless containers amphipods were quiescent during the day, clumping together. At night such clumps dispersed and exploratory activity increased. Swimming was never observed, and when out of water these talitrids hopped rarely. Tussock grass and macroalgal debris dominated their gut contents in situ, with terrestrial plant debris increasing in prominence in amphipods from higher upshore. Feeding trials revealed high consumption of rotting tussock grass debris and green algae (Ulothrix, Ulva). Soft materials 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 time. Fecundity is linearly related to female body length. Eggs more than double in volume during development.

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