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Assessing sea floor functional biodiversity and vulnerability

Olivier Beauchard*, Murray S. A. Thompson, Kari E. Ellingsen, Gerjan Piet, Pascal Laffargue, Karline Soetaert

*Corresponding author:

ABSTRACT: The marine benthos has been largely studied through the use of response traits that characterise species vulnerability to disturbance. More limited has been the specific use of effect traits that represent other species descriptors and that express ecosystem functions. In the sea floor, the benthos is a key ecosystem engineering component of which functions can be relevantly derived from effect traits. This study provides a typology of sea floor functions based on an extensive data compilation of effect traits. 812 benthic invertebrate species from the northeast Atlantic were documented for 15 effect traits expressing substratum alteration and habitat creation. Cluster analysis identified 15 species groups that represented various epi- or endobenthic functions. Beyond function-habitat specificity, we show that soft sediment species exhibited broader functional niches in the trait space that increase multi-functionality, and were endowed with rare combinations of traits that expanded the functional extent of the species assemblage. As a consequence, soft sediments can host a higher functional diversity than hard substrata because a wider range of above- and below-substratum activities in soft bottoms are possible. Then, based on response traits documented for the same species and used to express vulnerability to natural or human-induced disturbance, we showed that vulnerability within sea floor functions can be considerably variable. This can be consequent of the independence between the evolutionary nature of response traits versus the contingent engineering abilities of benthic species through effect traits. The paper brings theoretical and utilitarian clarifications on this trait dichotomy.