Spatial variation in kelp forest communities along the Big Sur coast of central California, USA

Abstract

Giant kelp [ Macrocystis pyrifera (Linnaeus) C. Agardh] forests are commonly called a community, but their composition varies among sites and depths. While numerous studies mention this variation and it is the descriptive basis for general models of kelp community structure, it has rarely been quantitatively assessed. We described kelp forest structure among four depths (6, 9, 12, and 15 m) at nine sites along 80 km of the relatively pristine Big Sur coast of California. Density and cover of common organisms were assessed in replicate quadrats at each depth in each site. Macrocystis pyrifera formed a surface canopy at eight sites, and bull kelp, Nereocystis luetkeana (Mertens) Postels & Ruprecht, at one site. The understory kelps Pterygophora californica Ruprecht and Laminaria setchellii P.C. Silva and the bat star Asterina miniata Brandt were the most abundant organisms counted as individuals. Geniculate and nongeniculate coralline algae and encrusting invertebrates had the highest cover. Abundances of giant kelp and the two understory kelps, and sessile invertebrates were significantly different among sites, and differences in sessile invertebrate abundance suggest two general ‘types’ of kelp forests in the region; one with abundant understory kelps and coralline algae and the other with an understory dominated by sessile invertebrates. Among the eight abundant taxa only the abundance of the two types of coralline algae varied significantly among depths when all sites were combined. Cluster analyses indicated two depth zones within these forests.