Distributional patterns and diets of four species of sea urchins in giant kelp forest (Macrocystis pyrifera) of Puerto Toro, Navarino Island, Chile

The distribution pattern of microhabitat and diet was studied in 4 species of sea urchins (Loxechinus albus, Pseudechinus magellanicus, Arbacia dufresnei, Austrocidaris canaliculata) in a forest of Macrocystis pyrifera in southern Chile. We conclude that: (1) There is no overlap in space utilization (microhabitat) except for the species pair P. magellanicus -A, canaliculata. (2) All 4 species of sea urchins feed on M. pynfera in different percentages; this results in a high diet overlap in at least 3 of them; however, this resource does not appear to be limiting. (3) Neither competition among adults nor predation on adults appears to be a key factor in regulating the present population densities of the four species of sea urchins in the habitat studied. Our results further indicate that differences in intensity of water movement, correlated with bathymetric distribution, regulate population density, size of test and biomass in these four species.