NESTLER, J.R.*; WHEELING, R.J.; BRIDGER, C.; Walla Walla College; Walla Walla College; Union College: Circadian Cycle of Activity and Metabolism in the California Sea Cucumber (Parastichopus californicus)

Sea cucumbers (Holothuroidea) are important in ocean communities by affecting physical and chemical characteristics of sediment through their deposit feeding activities. We examined the daily cycle of movement, feeding, respiratory activities, and metabolism in Parastichopus californicus, a common sea cucumber of the North American west coast. Twelve free-ranging cucumbers were individually tagged. Distance moved, feeding status, and cloacal status were determined every two hours for two 24 h periods. Mean rates of movement during daylight hours (0600-2000 h) ranged from 0.11 to 0.19 m/h. Mean rates of movement at night (2000-0600 h) were significantly higher (ANOVA, p<0.0001), ranging from 0.38 to 0.40 m/h. Feeding tentacles were more likely to be extended and the animals actively feeding during the night (60.0% feeding), while during the day the feeding tentacles were more likely to be withdrawn within the oral hood (24.0% feeding; Chi square=12.59, p=0.0004). Cloacas were more likely to be open during the night (76.3%) than during the day (31.0%; Chi square=19.95, p<0.0001), allowing gas exchange through the respiratory trees. Metabolic rate was measured in situ in eight cucumbers during the day (0800-1800 h) and eight additional animals at night (2300-0400 h). Oxygen consumption at night (0.066 mg O₂/g/h) was more than double the daytime rate (0.031 mg O₂/g/h; t-test, t = 3.898, p=0.0016). Several studies have examined activity patterns during daylight hours under the assumption that P. californicus is diurnal due to its conspicuous and apparently active behavior. However, the current study demonstrates that this species has significantly increased rates of movement, feeding and respiratory activity, and metabolism during the night.