SALINITY TOLERANCE, SALINITY PREFERENCE AND TEMPERATURE TOLERANCE IN THE HIGH-SHORE HARPACTICOID COPEPOD TIGRIOPUS-BREVICORNIS

Tigriopus brevicornis (O.F. Muller) were collected in 1992 from rock pools close to U.M.B.S. Millport, Isle of Cumbrae, U.K. and acclimated to various combinations of salinity and temperature for at least 1 wk prior to laboratory experiments. Higher salinities of acclimation enhanced tolerance to high salinity stress, while tolerance of low salinities was hardly affected by acclimation salinity. Acclimation to low temperature (10 degrees C) extended the survivable salinity range for T. brevicornis. High-salinity acclimation enhanced the survivable temperature range. Copepods acclimated to 60 parts per thousand survived significantly lower and higher temperatures than did 34 parts per thousand-acclimated individuals. At high temperature, 75 parts per thousand-acclimated female copepods had the highest median lethal temperature, 38.9 degrees C. Females were significantly more resistant to high temperatures than males. The copepods were seen to have a very low median lethal temperature when frozen into solid ice for 2 h; 50% mortality occurred at -16.9 degrees C in 10 degrees C, 34 parts per thousand-acclimated T. brevicornis. Salinity preference experiments demonstrated an ability to discriminate between salinities differing by as little as 3 parts per thousand. Copepods acclimated to 34 parts per thousand chose salinities near their acclimation salinity; individuals acclimated to 5 parts per thousand favoured slightly higher salinities, while copepods acclimated to 60 parts per thousand chose rather lower salinities.