Abstract
Several forms of calcifying scleractinian corals provide important habitat complexity in the deep-sea and are consistently associated with a high biodiversity of fish and other invertebrates. How these corals may respond to the future predicted environmental conditions of ocean acidification is poorly understood, but any detrimental effects on these marine calcifiers will have wider impacts on the ecosystem. Colonies of Solenosmilia variabilis, a protected deep-sea coral commonly occurring throughout the New Zealand region, were collected during a cruise in March 2014 from the Louisville Seamount Chain. Over a 12-month period, samples were maintained in temperature controlled (∼3.5 °C) continuous flow-through tanks at a seawater pH that reflects the region’s current conditions (7.88) and an end-of-century scenario (7.65). Impacts on coral growth and the intensity of colour saturation (as a proxy for the coenenchyme tissue that covers the coral exoskeleton and links the coral polyps) were measured bimonthly. In addition, respiration rate was measured after a mid-term (six months) and long-term (12 months) exposure period. Growth rates were highly variable, ranging from 0.53 to 3.068 mm year−1 and showed no detectable difference between the treatment and control colonies. Respiration rates also varied independently of pH and ranged from 0.065 to 1.756 µmol O2 g protein−1 h−1. A significant change in colour was observed in the treatment group over time, indicating a loss of coenenchyme. This loss was greatest after 10 months at 5.28% and could indicate a reallocation of energy with physiological processes (e.g. growth and respiration) being maintained at the expense of coenenchyme production. This research illustrates important first steps to assessing and understanding the sensitivity of deep-sea corals to ocean acidification.
Highlights
Deep-sea corals (Phylum Cnidaria) are an abundant and diverse group that are found worldwide and, like their shallow water counterparts, several groups are characterised by their ability to form calcium carbonate skeletons
One study by Thresher et al (2011) in nearby Australian waters investigated the effects of chronic low carbonate saturation levels on the distribution, growth and skeletal chemistry of several deep-sea corals off southeastern Tasmanian seamounts and found that the distribution of scleractinian corals is constrained by low carbonate saturation levels
A recent synthesis assessed the potential threat posed by ocean acidification (OA) to the diversity and productivity of New Zealand marine ecosystems, including corals, and highlighted the knowledge gaps in understanding the impacts (Law et al, 2018)
Summary
Deep-sea corals (Phylum Cnidaria) are an abundant and diverse group that are found worldwide and, like their shallow water counterparts, several groups are characterised by their ability to form calcium carbonate skeletons. Deep-sea corals are generally found in water temperatures between 4 and 12 ◦C (Roberts, Wheeler & Freiwald, 2006; Buhl-Mortensen & Mortensen, 2005). This largely corresponds to relatively shallow depths (between 50 and 100 m) at high latitudes, and greater depths (up to 4,000 m) at low latitudes (Roberts, Wheeler & Freiwald, 2006). Compared to the large numbers of shallow-water, reef building corals that have been described, only 10 deep-sea scleractinian reef-building species have been described globally (Cairns, 1979; Freiwald et al, 2004)
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