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A dynamic world for deep, cold-water corals

28 August 2013

A recent study off the coast of Scotland has provided the clearest picture yet of the highly dynamic conditions faced by cold-water corals. The research, as part of the UK Ocean Acidification research programme (UKOA) and published in Global Change Biology, has shown that corals at this cold-water site experience a more variable environment than previously thought; an important consideration when making predictions about future conditions with respect to the response of marine ecosystems to ocean acidification* and climate change.

As a habitat cold-water corals are just as important as their tropical, shallow-water cousins, but studies of them are still in their infancy due to their deep, largely inaccessible locations. Cold-water corals enhance deep sea ecosystems and provide a vital nursery habitat and refuge for many commercial fish as well as being home to a whole host of other deep sea organisms; a habitat which would otherwise be a dark, underwater desert.

Dr Helen Findlay from Plymouth Marine Laboratory, accompanied by scientists from Heriot-Watt University, National Oceanography Centre, Southampton and the Scottish Association for Marine Science, spent 10 days at the Mingulay Reef Complex (NW of Scotland) studying the carbon and nutrient dynamics, which are highly variable in this area. This is as a result of a tidal downwelling; when the surface water is “pulled” into the depths due to a wave of tidal water passing over structures on the seabed. In the case of the Mingulay Reef Complex, this downwelling is known to supply warmer, oxygenated, plankton-rich waters to the corals growing on the reef as well as causing short-term changes in the surrounding acidity; a shift that is the equivalent to a 25 year leap into the future with respect to projected levels of atmospheric CO2.

Maps of the study site location (a) shown in relation to UK (b) off the coast of Scotland (c) bathymetric map of the MingulayThis natural site study showed that the daily fluctuation in conditions was more than double that expected for waters at this depth and is nearly 4 times greater than the seasonal variation projected by computer models. It also highlights the methodological challenges for short-term laboratory experiments on slower growing organisms, such as cold-water corals, as they may not have the time to respond to the altered conditions.

The study identifies that further research is required to assess the impact of multiple stressors, such as the combination of warming and ocean acidification as a result of increasing CO2 emissions, on cold-water corals as well as a wider range of time-scales in lab-based experimental studies. Investigations should also be supported by continued monitoring of these ecologically and biologically significant habitats, all of which will help further our understanding of how they will respond to the changing ocean.