HUMAN DISTURBANCE AND LONG-TERM CHANCES ON A ROCKY INTERTIDAL COMMUNITY

The effects of human recreational activities on a rocky intertidal habitat on the coast of San Diego, California, USA were investigated. Organisms susceptible to collection for food, bait, or aquaria were identified and served as key species for the study of biota disturbance. This study examined three major aspects: (1) Distribution and activities of people along the shoreline were documented. (2) Distribution and density of echinoderms and molluscs inhabiting the cryptic underrock surface were sampled along an identified gradient of disturbance. (3) Densities of conspicuous organisms inhabiting the underrock surface at the most disturbed location detected in the spring of 1971 were compared with those detected in the spring of 1991. Surveys of human activity made during weekends with low tides exposing most of the intertidal zone (below 0 MLLW) during the daylight hours between December 1990 and August 1991 showed a definite pattern. People concentrated in an area with a 200 m radius centered on the primary accesses; areas farther from these points were less visited. The study site stood along a gradient of human disturbance, and the sampling of organisms along this indicated a gradient of biota disturbance as well. The density of all species was reduced in the more heavily visited intertidal area. The underrock community at the most heavily visited location changed substantially from spring 1971 to spring 1991. The density of most of the macroorganisms decreased between the two dates, with the exception of the density of small gastropods, which increased. Even if more long-term studies are needed for determining the actual status of communities under the influence of human disturbance, the combination of spatial and longterm studies shows the importance of setting better policy and establishing more effective reserves in order to enhance and maintain species diversity and density.