Unexpected effects of coastal storms on trophic ecology of two rocky reef fish species

Coastal storm risks have been increasing over the last couple of decades, affecting both marine infrastructure and human security. Nevertheless, the ecological impact on intertidal marine fishes has not been addressed yet. We carried out a field experiment during austral summer 2018, using statistical wave parameters, characterizing coastal storms as a factor, and the gut content of two sympatric intertidal triplefins, Helcogrammoides chilensis and Helcogrammoides cunninghami, as a proxy for trophic interactions. Three locations were sampled before and after the arrival of three consecutive summer coastal storm events. From all gut contents, a total of 16,597 prey items were found. Both species are micro-carnivorous, predating mostly on harpacticoid copepods, amphipods and chironomid larvae, without significant differences in prey composition with the passing of the summer coastal storms. However, after coastal storms, heavier-at-length fish (0.05–0.5 g weight gain) were found in the intertidal. Indeed, after the impact of the coastal storms, H. chilensis increased their ingestion of larger prey (amphipods, chironomid larvae), while H. cunninghami decreased the number of prey ingested. When compared between species, the feeding success after the passing of coastal storms was greater for H. chilensis than H. cunninghami. Finally, trophic overlap between species was high, but after the coastal storms passed, it decreased noticeably due to small changes in proportion of large chironomid and gammarid amphipods in the diet. Therefore, summer coastal storms affected the foraging behavior, increasing the weight of two recurrent cryptobenthic rocky reef fish from central Chile. In a broader ecological context, the shift from pelagic (i.e., copepods) to benthic prey (i.e., amphipods, polychaetes) may change the relative contribution and the subsidy production in nearshore habitats via pelagic-benthic coupling.