Studies of Food Preference in Algivorous Invertebrates of Southern California Kelp Beds

Stands of the giant kelp, Macrocystis pyrifera, frequently suffer attack by grazing organisms and in some cases complete destruction has been observed. The present investigation of the feeding habits of grazing organisms is primarily concerned with food preferences. Discrimination in choice of plant foods was examined in 11 common invertebrate species of the sublittoral rock bottom fauna of southern California by measuring the differential consumption of seven common algal species in the laboratory. The algae were selected as representing the major floral elements of the kelp bed (Macrocystis pyrifera) community. All of the grazers exhibited high degrees of preference for Macrocystis. Shallow water grazers revealed stronger preferences for Egregia than for Macrocystis. Herbivores found at greater depths indicated strongest preferences for Macrocystis, Laminaria, and Pterygophora, plants that are generally common at these depths . The deepest-living herbivore, Lytechinus, showed greatest preference for a red alga, Gigartina; red algae generally supplant brown algae in dominance at greater depths. Some of the invertebrates refused certain of the marine plants. A specific distaste factor may exist in these cases