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Changes in benthic community structure are strongly related to environmental factors, and we need to determine how these natural changes occur in order to interpret the possible changes associated with anthropogenic impacts. The aim of this survey was to characterize and classify the polychaete assemblages inhabiting unpolluted soft bottoms in the Spanish Mediterranean in relation to environmental factors. Thirteen localities were sampled at depths between 9 and 31 m, from 2004 to 2006. Multivariate techniques showed that the structure of polychaete assemblages detected in 2004 was consistent over time and correlations between polychaetes and environmental factors were detected. The study area comprises four kinds of communities mainly characterized by polychaete assemblages, sediment types, and depth. [ABSTRACT FROM AUTHOR]

Spatial and temporal variations in the distribution of the grain-size characteristics of surficial sediments were studied and the areas susceptible to contamination associated with fine-grained sediments were identified in Cullera Bay, Spain. We analyzed 90 sediment samples collected during six sampling campaigns in July (mid-summer), September (end of summer) and November (mid-autumn) 2002, and February (mid-winter), April (mid-spring) and July 2003. Different methods of grain-size analysis (bivariant analysis and discriminant functions) were applied to interpret the environments and mechanisms of sediment deposition. To identify zones that showed greater susceptibility to contamination by toxic substances associated with fine-grain sizes, contour maps of sediment distribution were prepared for the six sampling campaigns. The surficial sediments at Cullera Bay were classified according to the deposition scenario into shallow marine deposits and fluvial sediment deposits associated with the Júcar River discharge. The spatiotemporal variation showed that coarse sediments concentrated in the area nearest to the river mouth, whereas the finest sediments concentrated in the central and northern areas of the bay during the dry season, making them susceptible to contamination by harmful substances associated with the fine-grained fraction. [ABSTRACT FROM AUTHOR]