Abstract
The soft-bottom macrobenthos of Bahía San Julián intertidal was surveyed to identify infaunal assemblages and analyze their relationships with the main environmental factors determining species distribution. Four seasonal surveys (summer, autumn, winter and spring) were performed in the middle and lower intertidal levels at seven sampling stations established on both sides of an urban sewage discharge point, and water and sediment variables were measured. To explore possible spatial variations in the community, environmental and biological data were analyzed using univariate and multivariate statistics. Community composition varied with intertidal level, sediment characteristics and distance to sewage discharge site. In sediment with high mud content, the community was characterized by Darina solenoides, Mysella patagona, Eteone sculpta, Scolecolepides uncinatus and Capitella sp., in the middle intertidal, and was characterized by M. patagona and Ampelisca sp. in the lower intertidal. In sediment with dominance of fine sand, the community was characterized by Aricidea sp. at both intertidal levels. Near the effluent discharge site, the community was largely dominated by M. patagona. Intertidal level and sediment particle size are the main factors determining the composition of benthic assemblages in the study area. Sewage discharge also affects the composition of the infaunal community, possibly as a result of the contribution of particulate organic matter in suspension that stimulates the populations of detritus feeders.
Highlights
The distribution of benthic communities in tidal flats has been studied both in temperate and tropical regions (e.g., Beukema 1976, 1989; Armonies & Hellwig-Armonies 1987, Reise, 1991, Dittmann 2000, 2002; Dittmann & Vargas 2001)
The substrate in the intertidal flat was dominated by mud and fine sand, which together accounted for almost 100% of the sediment at all sampling stations (Table 1)
Principal component analysis (PCA) showed spatial variations in sediment composition; PC1 and PC2 axes explained more than 76% of the variance in the data
Summary
The distribution of benthic communities in tidal flats has been studied both in temperate and tropical regions (e.g., Beukema 1976, 1989; Armonies & Hellwig-Armonies 1987, Reise, 1991, Dittmann 2000, 2002; Dittmann & Vargas 2001). Several studies suggest that tidal height, time of exposure, and substrate characteristics, such as particle size composition of sediment, are the main factors determining composition and distribution of benthic communities in these environments The responses of benthic communities to a certain process of environmental degradation vary between geographical areas, depending on the specific composition of the natural community, the biological and ecological characteristics of the species, and the environmental conditions
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