Effects of Fluctuating Salinity, Nutritional State, and Temperature on Leptasterias Spp. From Little Port Walter, Alaska.

The effects of fluctuating salinity, nutritional state, and temperature on activity, oxygen consumption, feeding, and growth rates were analyzed on seasonally collected Leptasterias spp. (Echinodermata: Asteroidea) from Little Port Walter, AK. Leptasterias aspera and L. epichlora were collected on June 10, 1994, divided into size groups, and perivisceral fluid osmolality was measured every three hours during a 12 h 30-10-30‰S fluctuating cycle. The perivisceral fluid osmolality of larger individuals fluctuated less than that of smaller sea stars. The perivisceral fluid osmolality of small and large Leptasterias spp. closely tracks the ambient water osmolality during tidal cycles. Leptasterias spp. were collected on August 31, 1994 and separated into three nutritional treatment groups and analyzed over 31 days. Starved individuals had lower oxygen consumption rates than fed individuals. Feeding and starvation data suggest that Leptasterias spp. from Little Port Walter can survive beyond 31 days with a negative energy budget. For studies of temperature acclimation, Leptasterias spp. were collected at the annual temperature minimum (1°C; 19 November 1995, 27 February 1998) and the annual temperature maximum (12°C; 1 September 1996, 2 July 1997). Individuals from seasonal collections were step-wise acclimated (2°C every two days) or acutely exposed to 5°C, 7.5°C, 10°C, 12.5°C, 15°C, 17.5°C, 20°C, or 22.5°C. The 28-day LC50 of winter acclimatized, acutely exposed animals were 8 and 10°C lower than summer acclimatized, step-wise acclimated and summer acclimatized, acutely exposed individuals, respectively. Acute exposure and step-wise acclimation to experimental temperatures above the normal environmental maximum, 12.2°C, resulted in suppressed feeding and elevated oxygen consumption rates. Leptasterias spp. exist near the upper limit of capacity adaptation when environmental temperatures reach the annual summer maximum and undergo seasonal acclimatization to water temperature. Leptasterias spp. are adapted to withstand sublethal temperature shifts, which occur both seasonally and diurnally in the intertidal zone. Activity only partially correlated with environmental changes (temperature exposure, fluctuating salinity, and nutritional state of the animal). Reduced salinity negatively affected activity in Leptasterias spp. Activity coefficients varied with starved and fed feeding regimes, but were not significantly different between feeding treatments or time. Activity coefficients of Leptasterias spp. did not vary significantly with temperature