Effects of human trampling on macro- and meiofauna communities associated with intertidal algal turfs and implications for management of protected areas on rocky shores (Southern California)

Human visitation to coastal rocky shore ecosystems has numerous impacts via activities such as harvesting, rock-turning, pollution, and trampling. Human trampling, in particular, has been suggested to decrease the density and diversity of rocky shore organisms, especially large foliose algae. Inconsistent results have been seen in studies of the effects of human trampling on coralline algal turfs and the invertebrate communities (macro-and meiofauna) that inhabit them. Here, a relatively long-term manipulative trampling study based on realistic levels of human visitation was conducted in intertidal areas off Southern California dominated by coralline algal turf. Experimentally trampled plots ('impact plots') and control plots protected from foot traffic ('protected control plots') on turf-covered rocky intertidal benches were observed for 17 months in an area closed to human visitation. Control plots were also established at several other open-access sites ('open-access control plots') to determine whether patterns at the experimentally trampled site resembled those from sites where human visitation is allowed. Bare space increased in trampled plots as compared to pre-impact levels, but the percentage of bare rock in control plots did not change significantly. Trampled plots exhibited shifts in invertebrate community composition and significant declines in the abundances and richness of invertebrate taxa as compared to protected control plots throughout the experiment. Additionally, the trajectory of invertebrate community change through time in trampled plots was significantly different than that of both protected and open-access control plots. Nine months after trampling had ceased, the structure of the invertebrate communities from trampled plots was similar to protected control plots and bare space had decreased to pre-impact levels (ANOSIM analysis). However, trampled plots had significantly more taxa and higher Shannon diversity values than controls. These results indicate that to manage visitor impacts on rocky shore communities, 'no-access' zones may be as important as 'no-take' zones. However, the rapid recovery seen here also indicates that perhaps rotating or seasonal closures might be an effective management strategy to protect turf communities.