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Patterns in macrobenthic diversity in the lower shore of northeastern Atlantic macrotidal sandy beaches

Adeline Tauran*, Nolwenn Quillien, Jacques Grall

*Corresponding author:

ABSTRACT: Although knowledge of sandy beaches has increased recently, the benthic diversity of macrotidal sandy beaches in the northeastern Atlantic Ocean (more specifically, the western Channel and the northern Bay of Biscay) is poorly known. We present here a regional scale account of the species diversity, both observed and estimated, of the macrobenthic fauna of Brittany, based on an analysis of a species-level dataset from 18 sandy beaches in Brittany that were sampled annually for 13 years on the lower shore. In total, 526 species were identified, including 210 Annelida, 167 Arthropoda, 103 Mollusca, 19 Echinodermata, and 27 species of other phyla. Four distinct habitats were distinguished based on their benthic communities and characterised using environmental variables. Sediment heterogeneity appeared to enhance diversity as heterogeneous muddy sand harboured significantly more species than (muddy) fine sand. The role of environmental variables as structuring factors of benthic communities was investigated using redundancy analysis and variance partitioning. Beach morphodynamics and sediment structure explained most diversity variations (25.40% and 24.91%, respectively) followed by wave characteristics (13.46%). Finally, we offer some habitat-specific reference values regarding species richness and Shannon index for M-AMBI computation during Water Framework Directive and Marine Strategy Directive evaluations for a more reliable characterisation of sandy beaches' ecological status.