Digestion of the Alga, Macrocystis pyrifera, by the Sea Urchin, Strongylocentrotus purpuratus

Abstract

IT has been known for some time¹ that sea urchins when fed and then starved seem to retain for long periods the food present in the intestine. Furthermore, in vitro experiments have shown that a battery of digestive enzymes exist, some of which can digest complex polysaccharides such as iridophycin¹ and algin². During a series of experiments on the digestion of various substrates by sea urchins we had occasion to feed and afterwards starve an adult urchin and then recover all the material remaining after digestion. So far as we are aware no evidence exists on the percentage of algal food that can be completely degraded to assimilable products by a sea urchin. An urchin was prestarved until no fæcal pellets were passed. The animal, a female, weighing 99.3 gm., test height and test diameter measuring 26.5 mm. and 63.1 mm. respectively, was then fed a 33.3 mgm. (dry weight) piece of Macrocystis pyrifera, a food for which the sea urchin exhibits a high degree of preference³, and fed no further food for 18 days. The algal piece was consumed within 8 hr. No fæcal pellets were passed during the observation time, and the animal was killed at the end of this time.