Effects of temperature and the presence of benthic predators on the vertical distribution of the ctenophore<Emphasis Type="Italic"> Pleurobrachia pileus</Emphasis>

This study details the investigations of the effect of temperature and the presence of predators on the vertical distribution of the ctenophore Pleurobrachia pileus. Previous studies had suggested that P. pileus moves to the sediment when exposed to colder temperatures as an energy saving strategy. Although we did observe an effect of temperature on the movement of the ciliate combs, the effect of temperature on the average depth of animals in the water column was not significant, but a significant interaction was found between temperature and exposure time. In the presence of benthic predators or of water previously inhabited by these predators P. pileus changed its vertical distribution significantly, and moved away from the sediment, thus reducing the risk of being predated. We conclude that P. pileus can sense the presence of its predators, and changes its behaviour accordingly.Communicated by O. Kinne, Oldendorf/Luhe