Spatiotemporal variability of some shallow-bottom macroinvertebrates (Gastropoda, Bivalvia and Echinodermata) from Espíritu Santo Archipelago, Baja California Sur, Mexico

Four surveys (October 2001, and January, April and June 2002) were conducted at nine sites around the Espíritu Santo Archipelago, Baja California Sur, Mexico, to identify spatiotemporal variation patterns in the structure of the rocky, shallow-bottom macroinvertebrate community. The abundance of the conspicuous macrobenthos (gastropods, bivalves and echinoderms) was estimated visually by free diving at 4-6 m depth along two band-transects parallel to the coastline. Each transect was 5 m wide and 50 m long, covering an area of 500 m² per site. Sea surface temperature, wave exposure, type of substrate and slope were also recorded. Thirty-two species were identified. The echinoderms were the best represented group, with 18 species from 13 families, followed by the molluscs, with 14 species from 13 families. The highest mean abundance and density values were recorded for Tripneustes depressus (140.25 ± 64.21 ind and 0.28 ind m^-2, respectively). There were no significant differences in diversity, equitability and species richness among sampling months, though differences were found among sites (P <0.05). A spatial diversity pattern was identified, with low values (0.4 bits ind^-1) for exposed shores and high values (2.0 bits ind¹) for semi-protected areas.