Composition, richness and taxonomic diversity of Polychaete assemblages from La Paz Bay and adjacent oceanic areas of the Southern Gulf of California

Abstract

In the present study, the composition and structure of the assemblages of polychaetes of La Paz Bay and adjacent oceanic areas of the Gulf of California was analyzed. A total of 56 species belonging to 39 genera and 22 families were collected from eight stations sampled during the spring of 2006 at 31 to 208 m depth. Onuphidae (14 species), Paraonidae (7 species) and Spionidae (6 species) were the best represented families. The highest number of species and individuals (mean= 13 species station−1; 76.7 ind. 0.1 m−2) was found in stations located in the Gulf shelf while inside of La Paz Bay, the fauna was less abundant and diverse (mean= 9 species station−1; 47.0 ind. 0.1 m−2). Differences in species composition defined two main faunal groups, which were linked by their spatial distribution: assemblage Aricidea (Acmira) simplex – Aglaophamus verrilli inside the Bay, and assemblage Paraexogone molesta – Cirrophorus furcatus – Prionospio dubia in the Gulf shelf. The composition and structure of the fauna was mainly associated with the sediment type (Rho= 0.48; p=0.06): muddy habitats inside the bay and sandy bottoms in the Gulf. Only 11 out of the 39 identified genera (28.2%) had more than two species, and only seven of the 23 families (30.4%) had two or more species. This taxonomic heterogeneity caused a wide variability in the “average taxonomic distance” of every pair of individuals at each station (64.69 to 89.58). Therefore, the distribution patterns of the taxonomic diversity values between the sites inside La Paz Bay (mean= 79.45) and those found outside, in the Gulf (mean= 79.77), were similar.