On a global scale, cold-water reefs are at risk from ocean acidification caused by anthropogenic based rises in atmospheric CO2 levels (Turley et al., 2007).A consequence of this is a shallowing of the aragonite saturation horizon and under saturation of aragonite (Guinoette et al., 2006; Turley et al., 2007) as shown in Fig.10. Based on evidence from warm-water corals, changes to the chemistry governing calcification could have dramatic impact on the distribution and persistence of cold-water reefs. Indeed, information based on palaeographic studies combined with climate predictions suggest more than 70% of cold-water corals will be in locations that are under-saturated by 2099 (Guinoette et al., 2006), spelling a dire future for cold-water corals and the reef ecosystems. Carbon sequestration, a proposed method for capturing and storing rising CO2 emissions, could also adversely affect corals by lowering ocean pH but this is yet to be tested (Freiwald et al., 2004).
Ocean acidification is not the only issue with rising CO2 emission; changes in ocean currents and salinity could have a knock-on affect on cold-water reefs in a number of ways (Guinoette et al., 2006). Temperature rises pose a serious threat to calcification rates (Guinoette et al., 2006) and to the physiology of the corals. Experiments have shown that cold water corals e.g. L. pertusa have limited tolerance to changes in oxygen concentrations from rising temperatures (Dodds et al., 2007). Survival of the coral and hence the reefs long-term is likely to suffer as a result of metabolic stress to the corals (Dodds et al., 2007).The affects of climate change at the levels of local populations, habitats and wider reef ecosystem are currently unknown and require greater attention in future research. Overall, anthropogenic-based threats to cold-water coral reefs are complicated and extensive issues, requiring more research to predict the consequences and implement conservation strategies.