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.

Response of Cymodocea nodosa to ocean acidification and warming in the Canary Islands: Direct and indirect effects.

As detected in warming and ocean acidification, global change can have profound impact on marine life. Its effects on seagrasses are becoming increasingly well-known, since several studies have focused on the responses of these species to global change conditions. However a few studies have assessed the combined effect of temperature and acidification on seagrasses. Overall in this study, the combined effects of increased ocean temperature and pH levels expected at the end of this century (+5 °C and pH 7.5) on Cymodocea nodosa from Canary Islands, were evaluated for one month through manipulative laboratory experiments. Growth, net production, respiration, gross primary production, chlorophyll-a concentration and its vulnerability to herbivory were quantified. Results showed a positive effect of decreased pH on growth and gross primary production, as well as greater vulnerability to consumption by the sea urchin Paracentrotus lividus. In contrast, increased temperature limited net and gross primary production. This study shows than in future scenarios, C. nodosa from the Canary Islands may be a losing species in the global change stakes.