Seasonal Variability in the Vertical Distribution of Benthic Macrofauna and Sedimentary Organic Matter in an Estuarine beach (NW Spain)
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This study was designed to investigate seasonal changes on food available for benthic consumers in relation to tidal levels and sediment depth in an estuarine beach. The relationships between the biochemical characteristics of sedimentary organic matter and benthic macrofauna were analyzed quarterly over 2 years (from January 1997 to January 1999), in an estuarine soft intertidal zone from the NW coast of Spain (42°64′04″N, 8°88′36″W). Sediment samples were collected to provide a two-dimensional view of macroinfauna distribution in the intertidal zone and its relationship with the quantity and quality of the organic matter. The nutritional value of organic matter (i.e., lipid, protein, and carbohydrate) and the content of chlorophyll a of the sediment were measured. Macrofaunal assemblages and food availability in the sediment were studied at three tidal levels on the shore: two intertidal and one supratidal. Macroinfauna and biochemical compounds showed a clear vertical stratification with the highest macrofaunal abundance at the superficial layer of the sediment, where redox potential discontinuity was also observed. Crustaceans were found mainly inhabiting the supratidal level of the estuarine beach, while polychaetes and mollusks occupied the intertidal level. Food availability, measured as biopolymeric carbon, and also chlorophyll a from the sediment were better related to macroinfauna abundance, biomass, and abundance of main taxonomic groups. Macrofauna assemblages showed particular distribution in both vertical and horizontal ranges suggesting specific preferences to several abiotic factors. No clear seasonal pattern was found in macrofauna and sedimentary organic characteristics suggesting that macrofaunal assemblages are controlled by complex and unpredictable factors, including small-scale changes in substrate and hydrological characteristics.
KeywordsEstuarine beaches Macroinfauna Spatial and temporal patterns Biopolymeric carbon Food availability NW Spain
The authors thank the “Benthos Team” from the University of Vigo for their assistance during sampling. We are grateful to three anonymous reviewers, whose critical and constructive comments strengthened this paper. This research was supported by the Regional Government of Galicia (PGIDIT02RMA30101PR) and the University of Vigo (C505 122F 64102). I.F. Rodil was supported by a Ph.D. grant from the Xunta de Galicia (programa María Barbeito).
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