Effects of water temperature on diurnal feeding activity of Japanese spiny lobster Panulirus japonicus

The diurnal feeding activity rhythm of the Japanese spiny lobster Panulirus japonicus was observed at a temperature of 22.1+/-1.1 degreesC and further the relation between feeding activity and water temperature was studied under laboratory conditions where the water temperature fell gradually from 23.3 to 7.9 degreesC. The experiments were conducted from November 1997 to February 1998. The feeding activity of lobsters was detected by measuring the tension of wire attached to the prey, Mytilus edulis. The deviation of measurements for each 15 sec segment was obtained and those larger than 0.5 g were assumed to represent lobster feeding activity. The occurrence frequency of these deviations for each 1 hour period was calculated and used as a measure of the lobster feeding activity. There is a clear trend that the feeding activity of the lobsters responds to the diurnal brightness variation 12L:12D; very low activity in the day period and high activity in the night period. The activity suddenly increases just after the night period starts and remains at a high activity level for 2 to 3 hours, and some activity remains for the first 1 hour of the day period. When the water temperature was lower than 13.7 degreesC, the accumulated feeding activity over a 24 hour period became zero. Above this temperature the feeding activity increases as the water temperature increases at a rate of from 10 to 12 frequencies degreesC(-1) (95% confidence interval).