The influence of a large SW Atlantic shelf-break frontal system on epibenthic community composition, trophic guilds, and diversity

Productivity gradients (i.e., through bottom-up control) have an important influence on variability in species diversity and community composition in marine systems. At the SW Atlantic shelf-break front (SBF), we hypothesized that a high and stable food supply in areas under the core of a frontal influence (F) promotes a different benthic community structure (i.e., species diversity, taxa biomasses, and composition of feeding guilds) than in areas located under marginal influences of the front (M). In 2007, we sampled 34 trawling stations located across the SBF to evaluate this hypothesis. We compared epibenthic community composition, diversity indices, and species and trophic guild biomass in F and M areas. We observed differences in community composition, predator biomass, and the biomass of some taxa. However, we did not detect any changes in diversity indices, suspension feeder biomass, or grazer-omnivore biomass. The scallop, Zygochlamys patagonica, sponges, and the brittle star, Ophiacantha vivipara, together with the sea star Diplasterias brandtii characterized frontal areas. Marginal areas were characterized by the scallop, Z. patagonica, the parchment worm, Chaetopterus variopedatus, the basket star, Gorgonocephalus chilensis, the sea urchin, Austrocidaris canaliculata, and the sea star, Ctenodiscus australis. These shifts in taxa were not always reflected in biomass differences between areas. These results demonstrate that spatial variations in oceanographic structure, even over spatial scales of tens of kilometers, can affect composition and shift species dominance in benthic communities.

Research highlights
► We assess composition and diversity indices of an epibenthic community at a front.
► We found two epibenthic assemblages associated with marginal and frontal areas.
► The front dynamic, via food supply shifts, can influence the epibenthic composition.
► Different mechanisms could allow similarities in diversity, evenness and biomasses.
► Small spatial variations of a front can generate community’s composition shifts.