Reef fish assemblages associated to new mat-forming zoantharian communities in the Canary Islands.

Proliferations of zoantharians along tropical and subtropical regions are increasingly common and usually associated with anthropogenic impacts and ecosystem degradation. In the Canary Islands, we studied how the dominance in the substrate of Palythoa caribaeorum and Zoanthus pulchellus affected fish communities. For that purpose, we recorded the composition and biodiversity of fish assemblages associated to both zoantharian and macroalgae dominated habitats. In general terms, we found significant reductions of total fish abundance and richness at P. caribaeorum dominated habitats compared with macroalgae stands. However, in terms of trophic structure, there were significant changes within both zoantharian habitats depending on their coverages of the substrate. Herbivores and small invertebrate feeders, which are more adapted to forage in the macroalgae canopy, were less abundant in zoantharian habitats. This study demonstrates that the increasing dominance of zoantharians throughout the archipelago restructure the ecosystems and impact the native fish communities, that may offer a positive feedback for invasive tropical species to thrive.