Northern North Atlantic biogenic habitat calcium carbonate production: geographic variation and vulnerability to climate change

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Calcareous algae and cold-water corals are habitat-forming organisms that produce calcium carbonate skeletons in the cold-water environments of the North Atlantic. Their ability to build skeletons, and for those skeletons to endure after the algae or corals have died, is crucial for their ability to form habitats and produce calcium carbonate sediments. Ocean acidification threatens skeleton formation, and especially the ability of skeletons to make a habitat that will remain after the algae or corals are dead.   Calcareous algae, and the calcareous soft corals that inhabit the cold waters of eastern Canada are particularly vulnerable to ocean acidification because their skeletons are composed of high-magnesium calcite. The goal of this research is to understand the current and predicted impacts of ocean acidification on the habitats formed by calcareous algae and cold-water corals. This research program will compare skeleton formation, post-mortem skeleton loss, and carbonate production across the natural ocean acidification gradient between the Northwest Atlantic (Canada, specifically Newfoundland and Labrador, and the Eastern Canadian Arctic) and the Northeast Atlantic (N Europe, specifically NW France). Furthermore, this research will examine the history of calcareous algae and cold-water coral-based ecosystems over the last several hundred to several thousand years. Sediment cores will be collected and analyzed from calcareous algae and cold-water coral habitats on soft bottoms to reveal how these habitats have evolved in relation to changing oceanographic or climatic conditions or changes in coastal land use.  In hard-bottom environments, we will use the chemistry of the calcareous algae or cold-water coral skeletons to reveal the records of past climatic or oceanographic conditions.  Pressurized aquarium experiments on dissolution of calcareous algae or cold-water coral skeletons under high CO2 conditions predicted under emissions reduction targets or business-as-usual will measure the response of cold-water coral skeletons to acidified deep oceans. Calcareous algae, especially unattached algae called rhodoliths, and cold-water corals are already threatened by direct impacts of human activities, such as bottom-contact fishing. Understanding and predicting their fate in relation to climate change and ocean acidification will help protect these habitats in the long term. The ability of rhodolith beds and cold-water coral forests to host other biodiversity depends partly on their ability to maintain a positive net carbonate budget, that is, to be producing more calcium carbonate skeletons and sediment than the carbonate lost to dissolution, biological erosion, and sediment export.    Hosting biodiversity supports fisheries.  Understanding the effects of ocean acidification on carbonate biogenic habitats will help protect biodiversity and sustainable fisheries in Atlantic and Northern Canada.