Soft-sediment benthic assemblages of Bahía de Navidad (Jalisco, México): spatial and seasonal patterns

Abstract

Spatial and seasonal patterns of benthic assemblages in a semiexposed sandy bay were analyzed in relationto sedimentary variables and organic load. Four sampling stations with different environmental conditions; sedimentsize, wave exposure and proxmity of freshwater runoff; were selected along the bay. Monthly samplings were carriedout during a year using a suction sampler. Sediment samples were also taken to analyze granulometry and organicload. For analysis purposes data were pooled according to climatic periods present in the area, dry season-winterand rainy season-summer. The north part of the bay showed fine sediment, silt and clay, with higher organic matterpercentage, doubling the south percentages during summer, higher density of macrofauna, with a clear dominance ofscaphopods and polychaetes; 88% of total abundance; and lower diversity and evenness. Scaphopods showed densitiesup to 9 788 ind·m-2. The south part of the bay showed coarser sediment; mainly fine sand; with lower organic mattercontent, lower macrofaunal density and higher diversity and evenness. Scaphopod densities were much lower in thisarea. High significant correlation was found between macrofaunal assemblages and the percentage of silt and organicmatter (Spearman rs= 0.94).