Biodiversity and structure of the polychaete fauna from soft bottoms of Bahia Todos Santos, Baja California, Mexico

This paper describes diversity patterns of the polychaete fauna in Bahía Todos Santos (Pacific Ocean, Baja California, Mexico). Thirty-nine stations were sampled in October 1994. Measurements of depth, temperature, salinity, dissolved oxygen, organic content and sediment particle size were made. Polychaetes constituted 64% of all invertebrate macrofauna, with 13,757 specimens in 44 families representing 203 species. The best represented families were Spionidae, Capitellidae, Paraonidae, Cirratulidae, Maldanidae, Ampharetidae and Nephtyidae. Bahía Todos Santos presented high species richness (species/station); values varied between 6 (near the harbor) and 67 species (next to Estero Punta Banda). Higher species richness values (48 species to 67/station) were located in the southern section of the bay. Abundances (individuals/station) were generally high (120–1434) except for some coastal stations. Nearly one-third of the stations presented <f>H′</f> values higher than 4.00. Diversity (<f>H′</f>) values ranged from 2.06 to 4.80; higher diversity values were found in the southern section of the bay.The stress-predictability modeling characterized approximately 70% of stations as presenting favorable and stable conditions. Pearson and Bray–Curtis coefficients separated stations in relation to their sediment particle size, depth and location in the bay. Principal component analysis determined that organic matter content, percentage of silt-clay, and water depth accounted for 95% of the total variance for all environmental factors measured. Correspondence analysis distinguished three groups of species: Group A species with an extensive distribution throughout the bay and relatively high abundances, Group B species abundant in the shallow areas, especially near the harbor, and Group C species present in the area of the submarine canyon. Non-metric multidimensional scaling analysis separated five groups of stations, depending on depth, grain size and location in the bay. Our results show that Bahía Todos Santos is a favorable environment for polychaete development, their distribution being strongly related to sediment characteristics. The dominant trophic group corresponds to deposit-feeders (91 species). [Copyright &y& Elsevier]