Spatio-temporal variability of micro- and meiobenthic communities in a White Sea intertidal sandflat

Meiobenthos (harpacticoids), microzoobenthos (ciliates) and microphytobenthos (epipelic diatoms and dinoflagellates) were collected during July 1999 using nested sampling at the scales of decimeters, meters and tens of meters. Similarity between samples decreased rapidly with distance for all groups, but unicellular organisms were distributed more heterogeneously at a large scale than meiobenthos. Microspatial (decimeter scale) variations contributed the main part of total variation of harpacticoid abundance, while the large-scale differences were less important. On the contrary, these differences yielded the main variability for ciliates and especially for microalgae. The relative role of temporal variability decreased steadily for the smaller-sized organisms. Stability of spatial structure at multiple scales was estimated by Mantel correlations, Rm, between the successive similarity matrices. For harpacticoids, the results showed intensive and chaotic turnover of microaggregations. For microbenthos, rather high Rm values were found in smaller scales: tens of metersdfor ciliates, from meters ondfor dinoflagellates, and already from decimeter scale and ondfor diatoms. Thus, the general spatial pattern (that is the arrangement of micropatches) was more stable for microbenthos than for meiobenthos. Temporal variability of species structure, in contrast to the spatial one, was highest for the smallest organisms. Correlations between size groups, using both total abundance and species composition, differed for microspatial, meso-spatial or temporal distribution. At the microscale, there were slight but significant negative correlations between harpacticoids and microalgae. Meso-scale distribution of dinoflagellates and diatoms differed significantly due to their different preferences in sediment properties. Ciliates were strongly positively correlated with dinoflagellates. At the microscale, each group had an individual community pattern. At larger scales, species composition of diatoms, ciliates and harpacticoids varied in space in coordination, while dinoflagellates behaved independently. It is hypothesized that body size determines the spatio-temporal scale of the perception of environmental heterogeneity.