Abstract
Despite the importance of deep-sea corals, our current understanding of their ecology and evolution is limited due to difficulties in sampling and studying deep-sea environments. Moreover, a recent re-evaluation of habitat limitations has been suggested after characterization of deep-sea corals in the Red Sea, where they live at temperatures of above 20 °C at low oxygen concentrations. To gain further insight into the biology of deep-sea corals, we produced reference transcriptomes and studied gene expression of three deep-sea coral species from the Red Sea, i.e. Dendrophyllia sp., Eguchipsammia fistula, and Rhizotrochus typus. Our analyses suggest that deep-sea coral employ mitochondrial hypometabolism and anaerobic glycolysis to manage low oxygen conditions present in the Red Sea. Notably, we found expression of genes related to surface cilia motion that presumably enhance small particle transport rates in the oligotrophic deep-sea environment. This is the first study to characterize transcriptomes and in situ gene expression for deep-sea corals. Our work offers several mechanisms by which deep-sea corals might cope with the distinct environmental conditions present in the Red Sea As such, our data provide direction for future research and further insight to organismal response of deep-sea coral to environmental change and ocean warming.
Highlights
The importance of deep-sea corals and the reefs they build is becoming increasingly evident[1, 2]
Rhizotrochus typus and Eguchipsammia fistula, two of the species identified in the Red Sea, are not Red Sea endemics
Domain enrichment was remarkably conserved across deep-sea corals and distinct from cnidarian genomic gene sets indicating that deep-sea coral have a common set of enriched functions
Summary
The importance of deep-sea corals and the reefs they build is becoming increasingly evident[1, 2]. Lowest measured oxygen concentrations for deep-sea corals from the Red Sea were below 1 mg/l4. At least seven distinct calcifying deep-sea coral species have been observed in the Red Sea so far[4, 5]. The Red Sea showed extreme tissue reduction, where individual corals were rarely covered by tissue below the growing edge of the polyps and different polyps were rarely connected by tissue[4]. This was offered as one possible adaptation to reduce metabolic demands in the oligotrophic, warm, and oxygen-depleted Red Sea deep-sea environment[4]. This adjustment might represent a case of extreme phenotypic plasticity, as regularly fed aquaria-reared coral specimens of E. fistula from the Red Sea displayed substantial tissue re-growth over the entire skeleton[8]
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