Distribution and trophic structure of benthic communities in a Patagonian fjord (Puyuhuapi Fjord, Southern Chile, 45°S).

Benthic marine food webs, which recycle organic matter and sustain unique biodiversity, are an important component of estuarine Patagonian fjords. These benthic communities in the Chilean Patagonia are highly diverse as the spatial variation of its habitats and food sources. Environmental stress from glacier melt and river discharge are known drivers of benthic community dynamics; However, other pressures such as salmon farming may be strongly influencing over benthic community structure. Under the above conditions, this study focus in described the trophic structure of the subtidal benthic communities in the Puyuhuapi fjord (45°S), evaluate primary food sources that support these communities using stable isotope Bayesian analyses, and identify key benthic species based on carbon and nitrogen stable isotopes as potential tracer associated to fish farm wastes. The results showed that in the Puyuhuapi fjord different environmental and anthropogenic forces act as drivers of changes in the structure and composition of the benthic communities, such as allochthonous sources of organic matter (OM) coming mainly from glaciofluvial discharges with high contributions of terrestrial OM and salmon farming waste. Briefly, carbon and nitrogen stable isotopes analyses revealed that the highly variable isotopic niche widths respond to food supplies from marine and terrestrial OM. In addition, particulate and dissolved waste from salmon farming activities were found to modify isotopic composition ratios in many suspension feeders. Particularly, our results indicate high δ15N values in the sponge Cliona chilensis and the encrusting coral Incrustatus comauensis, which appear to be potential ecological indicators for evaluating stoichiometry imbalances and trace organic pollution sources in fjord environments.