Corals respond to changes in their environment. This applies to both tropical and cold water corals and includes changes in temperature, salinity and pH levels, among other things. MARUM researchers, in a study led by Dr. Rodrigo da Costa Portilho-Ramos now investigated how warmer temperatures due to climate change affect cold water corals. To do this, they examined in detail how these corals have responded to environmental changes over the past 20,000 years. Their research has been published in the journal PLOS Biology.
Cold water corals and the species Lophelia pertusa in particular are the architects of complex reef structures. They lay the foundation for important habitats for deep-sea organisms that find both protection and food within the structures. However, coral reefs react very sensitively to changing conditions. These include warming ocean waters, acidification, declining oxygen levels and the variable food supply. A change in any of these parameters, for example due to global climate change, could affect the health of the entire coral reef. According to the new study, it is therefore important to understand exactly how these ecosystems respond to environmental changes in order to better protect them in the future.
First author Rodrigo da Costa Portilho-Ramos of MARUM – Center for Marine Environmental Sciences at the University of Bremen and his colleagues examined sediments from six cold-water coral sites in the North Atlantic and the Mediterranean to identify the critical parameters that could lead to the mortality and consequent proliferation of cold water corals. Information is stored in these sediments that provides insight into the environmental conditions of the past. This fact allows researchers to determine when and why cold-water corals flourished or not. The authors point out that the results could also be used to show how corals might respond to future climate changes. The study analyzes the changes in key environmental factors over the past 20,000 years, the period of global warming since the last ice age, and compares them with the occurrence of the cold water corals.
“We looked back into the past to understand how Lophelia pertusa responded to environmental changes,” says Portilho-Ramos. The corals disappeared from or returned to a region, mainly when the food supply or the oxygen content of the water changed. Cold water corals feed on microscopic plankton and other particles transported by ocean currents. The temperature and salinity of the water had little influence on the mortality or proliferation of cold water corals. As Portilho-Ramos points out, “we therefore assume that food supply and oxygen availability are the main factors determining the life or death of cold-water corals.” The long-term impact of ocean acidification is not clear, as there is no paleoceanographic indicator for this parameter.
As ecosystem engineers, cold water corals contribute significantly to the formation of biodiversity hotspots in the deep sea. With their influence on food webs and nutrient cycles, their role as fish farms and their impressive biodiversity, cold water coral reefs provide important ecosystem services. To continue these services in the future under the influence of climate change, the results of this research provide an important basis for developing knowledge-based management strategies for such deep-sea ecosystems. They also contribute significantly to the goals of the Bremen Cluster of Excellence, which is dedicated to the study of the ocean floor.
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