How cold-water corals are responding to global warming

Cold-water corals, and in particular the species Lophelia pertusa, are the architects of complex reef structures. They build the foundations of important habitats for deep-sea organisms that find protection as well as food in structures. Coral reefs, however, react very sensitively to changing conditions. These include warming ocean waters, acidification, declining oxygen content and variable food supply. A change in any of these parameters, as a result of global climate change, for example, can impact the health of the entire coral reef. According to the new study, it is therefore important to understand exactly how these ecosystems react to environmental changes in order to be better able to protect them more effectively in the future.

First author Rodrigo da Costa Portilho-Ramos of MARUM – Center for Marine Environmental Science at the University of Bremen, together with his colleagues, examined sediments from six cold-water coral sites in the North Atlantic and the Mediterranean to identify critical parameters that could trigger mortality and subsequent proliferation of cold-water corals. Information providing insight into past environmental conditions is stored in these sediments. This fact allows researchers to determine when and why cold-water corals thrived or not. The authors point out that the results could also be used to show how corals might respond to future climate change. The study analyzes changes in the most important environmental factors over the past 20,000 years, the period of general global warming since the last glaciation, and compares them with the presence of cold-water corals.

“We looked into the past to understand how Lophelia pertusa reacted to environmental changes,” says Portilho-Ramos. Corals have disappeared or returned to an area mainly when the food supply or the oxygen content of the water has changed. Cold-water corals feed on microscopically small plankton and other particles carried by ocean currents. Water temperature and salinity had little effect on cold-water coral mortality or proliferation. 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 type of impact of ocean acidification in the long term is unclear because there is no paleoceanographic indicator for this parameter.

Acting as ecosystem ‘engineers’, cold-water corals contribute significantly to the formation of biodiversity hotspots on the deep seabed. With their influence on food webs and nutrient cycles, their role as fish nurseries and their impressive biodiversity, cold-water coral reefs provide important ecosystem services. In order to continue these services in the future under the influence of climate change, the results of this study provide an important basis for developing knowledge-based management strategies for these deep-sea ecosystems. They also contribute significantly to the objectives of the center of excellence in Bremen, which is dedicated to the study of the seabed.

Original release:

Rodrigo da Costa Portilho-Ramos, Jürgen Titschack, Claudia Wienberg, Michael Georg Siccha Rojas, Yusuke Yokoyama, Dierk Hebbeln: Main environmental factors determining the life and death of cold-water corals through time. PLOS Biology 2022. DOI: https://doi.org/10.1371/journal.pbio.3001628

About MARUM:

MARUM produces fundamental scientific knowledge on the role of the ocean and the seafloor in the whole Earth system. The dynamics of the oceans and seabed have a significant impact on the entire Earth system through the interaction of geological, physical, biological and chemical processes. These influence both the climate and the global carbon cycle, resulting in the creation of unique biological systems. MARUM engages in basic and unbiased research for the benefit of society, the marine environment and in accordance with the United Nations’ sustainability goals. It publishes its quality-assured scientific data to make them accessible to the public. MARUM informs the public about new discoveries in the marine environment and provides practical knowledge through its dialogue with society. MARUM’s cooperation with companies and industrial partners is carried out in accordance with its objective of protecting the marine environment.

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Teresa H. Sadler