Spatial and bathymetric trends in composition and taxonomic diversity of Polychaeta (Annelida) assemblages from the deep Southern Gulf of California

Abstract

The deepsea fauna from the southern Gulf of California is currently poorly known, with only 193 species reported to date. The aim of this study was to analyze the composition, density, species richness, and taxonomic diversity (Δ) of the deepsea polychaetes of this region. Fifteen stations (238–2900 m depth) were sampled in 2012 and 2013. Eighty-four species from 58 genera and 26 families were identified. Density ranged from 4.76 to 42.86 ind 0.1m−2 and was not significantly correlated with depth; species richness ranged from 2 to 17 species per station, the lowest (2–6 species) occurring between depths of 651 and 915 m. Four assemblages were identified associated with depth (RANOSIM = 0.43, P = 0.002) and geographic position (RANOSIM = 0.56, P = 0.001): Prionospio elhersi–Subadyte mexicana–Syllis alternata (<350 m depth) and Aricidea sp. A–Ninoe jessicae (600–1000 m) in the western gulf; Onuphis similis–Aricidea (Acmira) simplex (1300–1600 m) and Aglaophamus paucilamellata–Sthenolepis spargens (>1200 m) in the middle gulf; stations 14A and 2A, sharing only their position at the far eastern gulf, remained isolated from any other assemblage. The highest diversity was found at 1300–1600 m (Δ = 86.1) and at >2000 m (Δ = 83–98) but decreased to Δ = 61.85 at 600–1000 m. The assemblage structure based on genera and family levels were similar to those based on species (Rho > 0.6), suggesting that either of the former two could be suitable surrogates for monitoring changes at the studied depths.