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Patterns in diversity and composition of the microbenthos of subarctic intertidal beaches with different morphodynamics

Andrey I. Azovsky*, Yuri A. Mazei, Maria A. Saburova, Philip V. Sapozhnikov

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ABSTRACT: Diversity and composition of benthic diatom algae and ciliates were studied at several beaches along the White and Barents seas, from highly exposed, reflective beaches with coarse-grained sands to sheltered, dissipative silty-sandy flats. For diatoms, the epipelic to epipsammic species abundance ratio significantly correlated with the beach index and mean particle size, while neither α-diversity measures nor mean cell length were related to the beach properties. By contrast, most of the characteristics of ciliate assemblages (diversity, total abundance and biomass, mean individual weight and percentage of karyorelictids) demonstrated a strong relationship to the beach properties, remaining low at the exposed beaches but increasing rapidly toward the more sheltered conditions. Beta-diversity did not correlate with the beach properties for either diatoms or ciliates. We suggest that wave action and sediment properties are the main drivers controlling the diversity and composition of the intertidal microbenthos. Diatoms and ciliates, however, demonstrate divergent response to these factors. Epipelic and epipsammic diatoms exhibit 2 different life strategies to adapt to their environments and therefore are complementarily distributed along the environmental gradient and compensate for each other in diversity. Most ciliates demonstrate similar mode of habitat selection but differ in their degree of tolerance. Euryporal (including ‘mesoporal’) species are more tolerant to wave action and therefore occur under a wide range of beach conditions, though their abundance and diversity are highest in fine, relatively stable sediments on sheltered beaches, whereas the specific interstitial (i.e., genuine microporal) species are mostly restricted to only these habitats.