Using habitat as a proxy for species diversity and species richness in marine reserve site selection for rocky intertidal areas of Laguna Beach
The annealing algorithm in MARXAN was used to build possible marine reserves by selecting the best of 26 heterogeneous rocky intertidal sites using various modeling parameters. Because comprehensive data on biological diversity is impractical to gather for large areas, four surrogate data sets were used to design marine reserves; habitat, substrate, mobile species abundance and sessile species percent coverage. Habitat data was quantitatively assessed for the entire 7.12 miles of Laguna Beach coastline. Habitat characteristics observed were; substrate type; formation type; slope; habitat heterogeneity; presence of microhabitats and wave exposure. The habitat data was used to develop a map and database of these heterogeneous intertidal areas in ArcGIS. Using the ArcGIS, substrate coverage in square feet was determined for each site. Species assemblage data was collected for 26 of the rocky intertidal sites. Macro-algae and macro-invertebrate abundance and coverage were quantified for a 30 m2 area of each site. Three transeets and nine quadrats were placed at random within the 30 rn2 area to determine mobile species abundance and sessile species percent coverage. Variable by site Multi Dimensional Scaling showed similarities between surrogates and Canonical Correspondence Analysis ordination displayed a significant correlation between substrate and species distribution. MARXAN was used to develop a network of sites for each biodiversity surrogate, conserving 10%, 30% and 50% of the surrogate input variables and minimizing the sites chosen. Mean species richness and diversity were higher in the sites chosen to be included in a reserve than outside a reserve, for the mobile and sessile surrogates. Mean species richness and diversity were higher for reserves designed based on species assemblages than reserves designed based on habitat or substrate, but not significantly so. These findings suggest that habitat level surrogates would be an effective method to identify valuable intertidal areas as high priority sites for inclusion in a larger MP A network. Site irreplaceability analysis determined that several sites were chosen > 65% of the time for all annealing runs. The habitat at these sites suggests that two different types of intertidal produce unique species assemblages: low sloping boulder fields and large areas of bedrock bench. Given that different habitats produce diverse species assemblages, it would therefore be important to include representatives of multiple intertidal habitat variations in a reserve network. Keywords Marine reserves, habitat diversity, species richness, species diversity, rocky intertidal habitat, marine protected areas, MARXAN, coastal resource management.