STUDIES ON THE BIOLOGY OF THE SEA URCHIN : V. FOOD CONSUMPTION OF STRONGYLOCENTROTUS INTERMEDIUS

Abstract

Some laboratory experiments concerning food consumption were carried out on Strongylocentrotus intermedius. The animals eat a wide variety of sea-weeds. The daily amount of food eaten per adult specimen (ca. 50mm in test diameter) varied largely among different kinds of sea-weeds ; the largest amount of food eaten was about 3g in wet weight when supplied with Laminaria japonica and the lowest was about 0.5g in Ulva pertusa. These values correspond to respectivelly 6 per cent and 1 per cent of the body weight of the sea urchin. Marked decline in the daily amount of food eaten per adult specimen of sea urchin was between July and October, while such decline was not recognized in the young specimen. The above restriction of the feeding of the adult urchins may bs attributed to some physiological factors correlated with gonadal development. The daily rate of feeding decreased as the urchin grew larger. However, there was no significant difference of sea urchins of different size in their ability to assimilate the food eaten. Assimilation efficiency increases with rising water temperature and vice versa ; the mean value of assimilation efficiency was about 70 per cent in summer and about 55 per cent in winter, when Laminaria japonica was supplied as food for the sea urchins. The amount (in dry weight) of food (Laminaria japonica) assimilated kept a high level (ca. 270mg/day/individual)during February to June and fell to about 50mg/day/individual in September and October.