First biological measurements of deep-sea corals from the Red Sea.

C Roder,M L Berumen,J Bouwmeester,A Al-Suwailem,E Papathanassiou,C R Voolstra

doi:10.1038/srep02802

C Roder, M L Berumen + Show 4 more

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https://doi.org/10.1038/srep02802

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Abstract

It is usually assumed that metabolic constraints restrict deep-sea corals to cold-water habitats, with ‘deep-sea’ and ‘cold-water’ corals often used as synonymous. Here we report on the first measurements of biological characters of deep-sea corals from the central Red Sea, where they occur at temperatures exceeding 20°C in highly oligotrophic and oxygen-limited waters. Low respiration rates, low calcification rates, and minimized tissue cover indicate that a reduced metabolism is one of the key adaptations to prevailing environmental conditions. We investigated four sites and encountered six species of which at least two appear to be undescribed. One species is previously reported from the Red Sea but occurs in deep cold waters outside the Red Sea raising interesting questions about presumed environmental constraints for other deep-sea corals. Our findings suggest that the present understanding of deep-sea coral persistence and resilience needs to be revisited.

Highlights

It is usually assumed that metabolic constraints restrict deep-sea corals to cold-water habitats, with ‘deep-sea’ and ‘cold-water’ corals often used as synonymous
While temperature in the aphotic zone of the Red Sea barely varies from 21.5uC and salinity below the thermocline increases to more than 40 PSU, oxygen concentrations were found to be lower than 2 mg l21 in subthermocline water (. 200 m depth), and at depths around 300 m declined even below 1 mg l21 (Fig. 1)
In accordance with what is known from the presence of deep-sea scleractinian corals elsewhere[2,8,29], deep-sea corals in the Red Sea were exclusively encountered in areas displaying strong topography such as steep walls or seamounts and attached to or associated with hard substrate, i.e. overhangs, rocks, edges, or faults

Summary

Introduction

It is usually assumed that metabolic constraints restrict deep-sea corals to cold-water habitats, with ‘deep-sea’ and ‘cold-water’ corals often used as synonymous. In addition to nutrient availability, the main factors determining coral settlement include temperatures not exceeding 12uC2,3,6, aragonite saturation[7], and sufficient oxygen levels[8]. While the latter two are vital to maintaining calcification and aerobic metabolism in corals, the low temperature regimes decelerate food decay and reduce metabolic demands. The ecology of the Red Sea is under-studied, outside of the Gulf of Aqaba[20] It is known for its extensive shallow water coral reefs of which some species are known to occur in depths outside the photic zone, in areas where available light is below 1% of that from the surface[21]. 1 22u46.0259N/ Sp A (Caryophyllidae) [JX629249] 600–700 on hard substrate, sometimes on sandy bottom and close to rocky structures

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