Corals in deep-water: will the unseen hand of ocean acidification destroy cold-water ecosystems?

Abstract

Listen

Translate article

Scleractinian cold-water corals, sometimes referred to as deep-water or deep-sea corals, form perhaps the most vulnerable marine ecosystems to the human dependence on burning fossil fuels (Guinotte et al. 2006). While coldwater corals were discovered two centuries ago, their significance in habitat formation is only just emerging with the deployment of manned and unmanned submersibles and the development of advanced acoustics to map their distribution (Hovland et al. 2002; Roberts et al. 2005; Grasmueck et al. 2006; Fig. 1a). They are found throughout the world oceans, usually between approximately 200– 1,000+ m depth, and unlike many warm-water corals do not contain photosynthetic symbiotic algae (Freiwald 2002 and see papers within Freiwald and Roberts 2005). They are long-lived (several 100 s of years old), form reef frameworks that persist for millennia and are thought to experience relatively little environmental variability (reviewed by Roberts et al. 2006). Reef-like structures can be sizable (e.g., the Rost Lophelia Reef off northern Norway is 100 km with some parts reaching 30 m off the seabed) and may cover a similar or even greater proportion of the oceans as warm-water coral reefs (Mortensen et al. 2001; Freiwald and Roberts 2005; Guinotte et al. 2006; Fig. 1c). Whilst only around 6 out of the 700 known species act as reef framework-forming species in deep waters, these deep-water reef structures are biodiversity hotspots and play an important role as a refuge, feeding ground and nursery for deep-sea organisms, including commercial fish (Rogers 1999; Fossa et al. 2002; Husebo et al. 2002). Little is known about the feeding behaviour of cold-water corals, but they are thought to depend on zooplankton and organic matter that sinks from the productive euphotic zone or organic matter laterally transported by currents for their nutritional requirements (Duineveld et al. 2004; Kiriakoulakis et al. 2004). They are therefore sensitive to changes in currents, surface ocean productivity and the strength of the biological pump of particles to deeper waters. Their slow growth and limited ability to recover make them particularly vulnerable to anthropogenic activities such as bottom trawling, seabed mining, cable and pipe laying, and oil and gas exploration. Some NE Atlantic deep-water reefs have now been severely damaged by bottom trawling (Rogers 1999; Roberts et al. 2000; Fossa et al. 2002; Hall-Spencer et al. 2002; Reed 2002; Freiwald et al. 2004; Wheeler et al. 2005). High atmospheric carbon dioxide concentrations caused by emissions from fossil fuel burning are now recognised to be the major cause of global warming, but these emissions are also acidifying our oceans (IPCC 2007). The oceans are a massive reservoir for CO2 and there is a flux Communicated by Editor in Chief B.E. Brown.