The second great challenge faced by marine dwellers is ocean acidification. What effect does this have on organisms?
In the process of ocean acidification carbon dioxide accumulates in seawater and enters the bodies of ocean dwellers. There it lowers the pH value of the bodily fluids and causes disorders in metabolism as well as, in the case of mussels, snails, sea urchins and corals, for example, disorders in the formation of calcareous shells. Among shell-forming organisms the so-called calcification decreases and thus also their ability to create powerful shells as supporting elements or as protection against predators. Corals in particular are important in this context as they build large-scale ecosystems. They are the engineers of the seas that create habitats for other species. These habitats are currently threatened by warming, acidification as well as by local pollution and invasive species.
Do some species also profit from ocean acidification?
There are species that benefit from ocean acidification. They primarily include species that take up carbon dioxide, carry out photosynthesis and, like macroalgae and seagrasses, do not build calcareous shells. If an algae species forms calcareous structures at the same time, its capabilities are impaired.
In the climate debate the Arctic is often compared to the “canary in the coal mine”. Does this metaphor also apply to ocean acidification?
We can assume that the concentration of atmospheric carbon dioxide is roughly balanced out worldwide. However, we have to take into account that the solubility of carbon dioxide varies according to water temperature. The gas not only dissolves extremely well at low water temperatures, but also in places where the seawater is diluted, or freshened so to speak, due to melting ice or increased precipitation. These two findings indicate that the Arctic is particularly hard hit because the two processes come together there. The Antarctic seas, too, can be described as significantly affected due to low temperatures.
You already said that different species react differently to the effects of climate change. Can you say anything about how the changes will impact ecosystems overall?
The varying geographic shift of species results in increasing mixing of ecosystems. At higher latitudes, for instance, species diversity increases. At the same time there is a displacement of the previously native species because they react sensitively to climate change and because many new species migrate into their habitat and compete with them. If, in addition to that, the oxygen-deficient zones spread, the areas in which bigger animals, including fish, can live, become smaller. This leads to a greatly reduced community of species and a dominance of unicellular organisms and bacteria.