Starfish: climate saver or climate victims?

Study provides first estimates of the impact of echinodermata on the marine ecosystem

Starfish © Stephanie Pohl, Sabrina Warnk, Alena Gall
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During their lifetime, they produce lime and bind carbon from the water column. When they die, it deposits on the seabed: animals like starfish and sea urchins, called echinodermata, apparently play a much bigger role in the global carbon cycle than previously thought. On the other hand, they are endangered by increasing ocean acidification. In a study in the journal "Ecology Monographs", an international research team has now presented initial assessments of their impact on the entire marine ecosystem.

In order to form their protective sheaths or skeletons, but also for various other processes, Echinodermata consume carbon from seawater. Starfish, sea urchins, snake stars, sea cucumbers and sea lilies belong to this group of animals, which is represented in all seas from the tidal range to the deep sea.

Calcification as a "hobby"

During calcification they absorb calcium and magnesium in different proportions into their bodies. Their skeletons thus include a significant amount of inorganic carbon that enters the water from the atmosphere. The echinodermata release this carbon to the ocean floor when they die.

Unlike the substance taken up by plankton or algae, it is not remineralized in the water column. The new study in the ESA Ecological Monographs is now the first evidence of the significant impact of Echinodermata on the organic and inorganic carbon budget in the oceans.

Uncertainties in the global calcium carbonate budget uncovered

"Our paper illustrates that we know little about the extensive carbon processes involving lime-forming species such as Echinodermata. This is one of the biggest uncertainties in the global calcium carbonate household. It is important to us that the contribution of the benthos, that is, the organisms living on the seabed, such as echinodermata, be reassessed on the global carbon cycle, "explains Mario Lebrato from the Kiel Leibniz Institute for Marine Sciences (IFM-GEOMAR). display

Models of the so-called "biological pump", which describe the uptake of CO2 and its conversion by algae and plankton, should in future also take into account organisms living near the ground. After all, they process more than a tenth of a gigaton of carbon per year, which far exceeds, for example, the contribution of foraminifera, the Kammerlingen, and is just below the total production in the entire water column. "We urgently need to gain more knowledge about the biochemical processes on the ground that are as important as the processes in free water, " continued Lebrato.

Ocean acidification with dramatic consequences?

Equally important to researchers is to learn more about the consequences of ocean acidification - a consequence of the extensive use of fossil energy sources - for echinodermata and other lime-forming species. First attempts suggest dramatic effects. Because when the pH of the water drops, it is more difficult for the organisms and finally even impossible to build up durable limestone structures.

The more research is done, the more contradictory trends emerge, making it harder to understand the process as a whole, Leb Lebrato adds. "Echinodermata are a good example of a species that shows unexpected patterns and challenges us as scientists."

(idw - Leibniz Institute for Marine Sciences, 14.01.2010 - DLO)