Temporal and spatial variation of an aquatic invertebrate community subjected to avian predation at the Odiel salt pans (SW Spain)

We studied the temporal variation in abundance and distribution of inverte- brates in the water column in both traditional and industrial salt pans in the Odiel marshes, south-west Spain, in 2001. We selected 12 ponds that were representative of different salinities and stages of salt production. Every two months, invertebrates were sampled within the 0 - 20 cm depth range used by foraging waders. We identified 40 taxa, including 30 aquatic and eight terrestrial metazoan invertebrates. Aquatic inverte- brate taxa richness and diversity decreased significantly with increasing pond salinity, whereas total biomass showed a non-significant increase. Overall, Artemia partheno- genetica constituted 67.6 % of invertebrates by number, and 95.5 % of the biomass. The copepod Cletocamptus retrogressus represented 31.1 % of invertebrates by num- ber, and 0.6 % of the biomass. Invertebrate biomass and dominance of A. parthenogen- etica was highest in September and lowest in November. There was significant spatial and temporal variation in abundance for all aquatic taxa, and for a given pond and month, the depth, distance to shoreline and fetch (wind effects) all had important par- tial effects on invertebrate distribution. Ordination methods showed a strong relation- ship between community structure and water chemistry (salinity, pH and redox poten- tial), with the salinity gradient being the most important. There was a clear separation between low salinity ponds with fish and submerged macrophytes and other ponds. The more intensively managed industrial salines held lower densities and biomass of invertebrates than traditional salines, perhaps owing to greater protection from wind or greater inputs of detritus. The beetle Ochthebius corrugatus was abundant in the tradi-