Allying physiology, ecology and phylogeny in hard corals (Anthozoa, Scleractinia): is ecophysiological evolution associated with tolerance to climate changes?

Abstract

A functional association established by the symbiosis between cnidarians and photosynthetic microalgae (known as zooxanthellae) is found in most shallow-water coral species. Regarding the energy supply, photosynthesis reaches up to 100% of energetic requirements in corals from strongly oligotrophic environments, while heterotrophy contributes up to 60% of the energy demand in eutrophic, turbid or deep waters. The physicochemical niche, therefore, can affect the coral-zooxanthellae relationship, promoting bleaching and/or reduction of calcification, although the overall physiological variability could be phylogenetically constrained. Here, we intend to evaluate selected ecophysiological traits in several scleractinian coral species from the oligotrophic environments of Bermuda - the northernmost coral reefs of Western Atlantic Ocean - under natural and simulated conditions of climate change. Such findings will be phylogenetically compared with data from the eutrophic waters of Brazil - the southernmost coral reefs [data already sampled]. We hypothesize that: (i) reef physicochemical nature has driven the evolution of photosynthesis/heterotrophy balance; (ii) antioxidant capacity and calcification rate correlate with the dependence level of heterotrophy; (iii) species from eutrophic environments are more tolerant to climate changes; and (iv) photosynthesis/heterotrophy balance, antioxidant capacity and calcification processes are evolutionary convergent. Little is known regarding the phylogenetic pattern of physiological resilience to climate change in corals from different environments and the relative influence of the physicochemical nature and/or phylogenetic history. Our future findings can propose some phenotypic responses as markers of sensitivity in a systematic framework for cross-species investigations, underpinning putative monitoring strategies in a clade-specific manner.