Diel activity of the sea cucumber Apostichopus japonicus is affected by the time of feeding and the presence of predators but not by time–place learning

Abstract

We examined the diel activity pattern of the sea cucumber Apostichopus japonicus with or without the presence of food and predators. We also tested whether they have the capability for time–place learning. In the feeding experiment, juvenile and adult sea cucumbers were fed at either 00:00 or 12:00, at a fixed feeding place for 12 days, and the presence of animals in the feeding area was recorded. In the predator experiment, juvenile sea cucumbers were kept in a tank with or without a filefish, and the emergence of juvenile sea cucumbers outside the oyster shell area was recorded. Juvenile sea cucumbers did not show a diel activity rhythm, whereas adults were nocturnal, but this was altered by feeding at 12:00. Neither juveniles nor adults appeared in the feeding area before feeding time, suggesting an inability for time–place learning. Juvenile sea cucumbers hid under the oyster shells during the daytime and were active at night in the presence of a filefish, but without a filefish, they also showed high activity in the daytime. We suggest that sea cucumbers change their activity depending on the presence of food and predators, but without the influence of time–place learning.