Small-scale spatial variation of macrobenthic community structure

Examination of small-scale spatial variation is essential to understanding the relationships between environmental factors and benthic community structure in estuaries. A sampling experiment was performed in October 1993 to measure infauna association with sediment composition and salinity gradients in Nueces Bay, Texas, USA. The bay was partitioned into four salinity zones and three sediment types. Higher densities of macrofauna were found in sediments with greater sand content and in areas with higher salinity. High diversity was also associated with high homogeneous salinity (31-33 parts per thousand) and greater sand content. Macrofauna biomass and diversity were positively correlated with bottom salinity, porewater salinity, and bottom dissolved inorganic nitrogen (DIN). Furthermore, species dominance shifted along the estuarine gradient. Streblospio benedicti dominated at lower salinity, but Mediomastus ambiseta and Mulinia lateralis were the dominant species at higher salinity. Statistical analyses revealed significant correlations for sediment characteristics (i.e., increased fine sediments, water content, and total organic carbon) with decreased total abundance and diversity. increased salinity and DIN were correlated with increased total biomass, diversity, and macrofauna community structure. These physico-chemical variables are regulated by freshwater inflow, so inflow is an important factor influencing macrofauna community structure by indirectly influencing the physico-chemical environment.