Vertical and horizontal distribution ofDesmophyllum dianthusin Comau Fjord, Chile: a cold-water coral thriving at low pH

Laura Fillinger,Claudio Richter

doi:10.7717/peerj.194

Laura Fillinger, Claudio Richter

Open Access

https://doi.org/10.7717/peerj.194

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Abstract

Cold-water corals provide an important habitat for a rich fauna along the continental margins and slopes. Although these azooxanthellate corals are considered particularly sensitive to ocean acidification, their responses to natural variations in pH and aragonite saturation are largely unknown due to the difficulty of studying their ecology in deep waters. Previous SCUBA investigations have shown an exceptionally shallow population of the cold-water coral Desmophyllum dianthus in near-surface waters of Comau Fjord, a stratified 480 m deep basin in northern Chilean Patagonia with suboxic deep waters. Here, we use a remotely operated vehicle to quantitatively investigate the distribution of D. dianthus and its physico-chemical drivers in so far uncharted naturally acidified waters. Remarkably, D. dianthus was ubiquitous throughout the fjord, but particularly abundant between 20 and 280 m depth in a pH range of 8.4 to 7.4. The persistence of individuals in aragonite-undersaturated waters suggests that present-day D. dianthus in Comau Fjord may show pre-acclimation or pre-adaptation to conditions of ocean acidification predicted to reach over 70% of the known deep-sea coral locations by the end of the century.

Highlights

Similar to their tropical counterparts and in spite of their lack of photosynthetic endosymbionts, azooxanthellate scleractinian cold-water corals (CWC) provide the structural 3-dimensional basis and habitat for a rich deep-reef associated fauna (Cairns & Stanley, 1982; Mortensen & Buhl-Mortensen, 2005; Roberts et al, 2009)
The persistence of individuals in aragonite-undersaturated waters suggests that present-day D. dianthus in Comau Fjord may show pre-acclimation or pre-adaptation to conditions of ocean acidification predicted to reach over 70% of the known deep-sea coral locations by the end of the century
As the quantity of CO2 absorbed by the ocean increases, the saturation state of the aragonite carbonate mineral used by scleractinian corals to build their skeleton decreases, leading to its dissolution

Summary

Introduction

Similar to their tropical counterparts and in spite of their lack of photosynthetic endosymbionts, azooxanthellate scleractinian cold-water corals (CWC) provide the structural 3-dimensional basis and habitat for a rich deep-reef associated fauna (Cairns & Stanley, 1982; Mortensen & Buhl-Mortensen, 2005; Roberts et al, 2009). As the quantity of CO2 absorbed by the ocean increases, the saturation state of the aragonite carbonate mineral used by scleractinian corals to build their skeleton decreases, leading to its dissolution (see e.g., Caldeira & Wickett, 2003; Orr et al, 2005). As carbonate solubility increases with decreasing temperature and increasing pressure, saturation states are lower in deep and cold habitats than in shallow and warm waters (Feely et al, 2004). Deep-dwelling cold-water corals are expected to be the first exposed to aragonite undersaturation (Doney et al, 2009)

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