How are your Cold-Water Corals Today?

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Deep sea corals provide important habitats for other marine animals

Being so far north of tropical coral reefs, some might ask “what corals?” But deep down – where you least expect it, in the cold waters of the North Atlantic – we find rich coral reefs and gardens in abundance, providing protection and important hunting and breeding grounds for a myriad of other animals, just like warm water corals.

Deep sea corals thrive between 40 and ca. 6000 meters below sea level, in temperatures as low as 4-5°C. The reefs’ framework mainly consists of stony corals, which can live in colonies or as solitary corals. Large cold-water coral reefs can be found along the coast of Norway, south of Iceland and, importantly, along the shelf edge west and south of Ireland. Extensive canyon systems connect this shelf with the deep sea and create perfect conditions for the deep sea reefs to propagate.

For decades, many fishing techniques, like trawling, destroyed huge parts of these unseen reefs and with them the fishing grounds they supported. However, awareness of this issue is increasing and larger areas of the ocean are now actively protected in the North Atlantic. The establishment of Marine Protected Areas (MPAs) provides one important basis for such protection.

With increasing ocean warming and acidification, however, a new threat arises. Like all marine animals with carbonate shells, stony corals are affected by the so-called calcite/aragonite saturation horizon (CSH/ASH) which defines the depth above which the mineralization of this shell material is possible. Warming oceans and shoaling horizons aggravate shell precipitation and force a migration into more favourable waters. We still have a very poor understanding of the dynamics of these deep sea environments and the mechanisms of coral growth as well as the short and long-term effects of environmental change. Recent research has focused on answering some of these questions.

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A Remotely Operated Vehicle (ROV) is used to study and sample the canyon environments at several thousand metres depth. Here, ROV Holland I is deployed from the RV Celtic Explorer, one of the Marine Institute’s research vessels.

In collaboration with the Marine Institute and the National University of Ireland, Galway, the Biogeochemistry Research Group at TCD has been investigating these environments and cold-water coral biomineralization processes. One aspect of ongoing investigations seeks to improve our understanding of growth patterns in the calcifying deep sea corals that build the framework of reef structures. This includes a closer look at species interactions and a comparison of different habitats. To collect the necessary data, members of the group participated in several research cruises to deep sea coral reef locations in Irish waters. Onboard a team of researchers from different disciplines and institutes works together to collect as much data as possible during their restricted time at sea.

While the 2012 cruise was complicated by storms, the most recent cruise of June 2013 met good weather, calm seas and few technical problems. Within the 3 weeks at sea we had the chance of successfully deploying the ROV (remote operated vehicle) over 10 times, gaining an insight into many areas of the canyons at different depths. This included measuring water parameters as well as investigating the biodiversity of the reefs. The findings can help improving our understanding of those deep sea environments and their vulnerability, as well as providing the necessary data for their better protection.

Authored by Alexandra Oppelt, PhD Student, TCD Geography

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