Effects of Giant Kelp (Macrocystis) on the Density and Abundance of Flshes in a Cobble-Bottom Kelp Forest
Abstract:The density of fishes was compared among regions with differing densities of giant kelp (Macrocystis pyrifera) at San Onofre Kelp bed (SOK), off northern San Diego county, California, during the fall periods of 1985 and 1986. Fish densities and the density of giant kelp were estimated by divers on belt transects. Bedwide (total) fish abundance was computed as the product of fish density and area of the respective kelp density region, summed over all regions of differing kelp density. Fish-kelp density relations were evaluated by ANCOVA and fish abundances compared between fall seasons by t-test, adjusted for unequal variances. Fish density was significantly related to the density of giant kelp for 18 of 30 life stages of the 14 major species tested; and in all 18 cases the relation was positive. Kelp-by-year interactions were significant for 15 life stages of 11 species. Year effects were apparent for 13 cases involving 8 species. Bedwide fish density was twice as great during the second versus first fall season. Bedwide abundances of fish were 75% greater (numbers) and 100% greater (biomass) during the second fall season, when both the density and abundance of Macrocystis at SOK was about half the respective value in fall 1985. Thus, more fish were concentrated within less kelp in the second year. The implications of these observations for describing fish-kelp relations are discussed.
Document Type: Research Article
Publication date: March 1, 1990
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