Benthic foraminiferal community changes and their relationship to environmental dynamics in intertidal muddy sediments (Bay of Cadiz, SW Spain)

The temporal and vertical variability of live intertidal benthic foraminifera was studied in parallel to environmental variables such as porewater and overlying water nutrients, salinity, temperature, sedimentary pigments and organic carbon. About 80% of benthic foraminifera were concentrated in the upper 0-4 mm sediment layer, which was also the maximum oxygen penetration depth under light conditions as determined by oxygen microsensor measurements. Significant changes in the composition of the foraminiferal community over the course of the study were found in the surface layer (0-2 mm), whereas no differences were detected in the deepest sediment layers (10-30 mm). Univariate measures, such as abundance, species richness and diversity showed few differences over time and little relation to environmental variables. On the other hand, multivariate regression analysis for the whole community assemblage showed that the significant community composition changes over time in the surface layer could be related to fluctuations of several environmental variables, mainly those related to sediment food availability. The macroalgal bloom that occurred during the winter months had no detectable effect on benthic foraminiferal abundance or community patterns. Overall, the intertidal foraminiferal community in the Bay of Cadiz showed a highly dynamic character and a clear vertical distribution which could be effectively captured by studying the uppermost sediment layer at sub-centimetric vertical resolution.