2023-06-11 00:05:36
The temperature of the oceans recorded a new record in May, due to global warming, which is not without consequences for marine plants and animals. Coral reefs are particularly threatened.
« She is good ? Yes, and even a little too much. Sea surface water temperatures hit a record high in May, following a previous record high in April, according to Copernicus, the European Union’s planetary observation programme, in a statement released on the occasion of World Oceans Day, June 8. Water above 21 degrees on average, warmer water means maybe a human dream, but it can turn into a nightmare for marine biodiversity.
A first consequence for the animals that inhabit the seas and oceans has already been observed for several years, in the northern hemisphere as in the southern hemisphere: forms of climatic migrations. Marine species move up north or down south to find cooler water. Conversely, in the Mediterranean, we have seen “via the Suez Canal, with the arrival of species originally living in the Red Sea,relief Serge Planes, research director at the CNRS. There is therefore necessarily a competition: the indigenous species of the Mediterranean find themselves having to share resources with these new species. »
A significant warming
Global warming, and therefore the warming of the water in the seas and oceans, can even influence the size of certain fish. According to a study by Ifremer, the French Research Institute for the Exploitation of the Sea, sardines have lost an average of 4 centimeters in 10 years, because the available quantity of microalgae, their food, is decreasing.
But the first victims of sea heat waves are coral reefs, a “structuring” species: a third of the planet’s marine species depend on them. The water here is shallow and warms up even faster. The corals bleach, and risk death, with the disappearance of the zooxanthellae. “This small unicellular algae in symbiosis with the coral provides the coral with what are called carbon chains: basically the sugar, the energy that the coral needs”, explains Serge Planes, a specialist in coral reefs in French Polynesia. The warming of the water leads to the disappearance of the zooxanthellae “and the coral will find itself with almost no partner to produce energy for it. You will then have a starving coral, which will, in quotation marks, “starve to death”, simply for lack of sugar, which leads to cell death and the death of the colony. »
Hope for corals
When sea heat waves are prolonged, the coral mortality rate exceeds 50%, “up to 70%”according to Serge Planes, also scientific director of the Tara mission in the Pacific, for whom all is not lost.
“We are not going to drastically change CO2 emissions, and we are therefore not going to drastically change the warming that we observe. On the other hand, in the next ten years, we can change certain behaviors which are all the other stresses that corals undergo: stress linked to pollution, stress linked to the transformation of watersheds and the supply of sediments… I think that’s what we have to play on to finally leave the coral reefs facing only one stress, climatic stress. And there we could make these coral reefs gain in resilience and allow them to finally pass the course of future sea heat waves. »
The human species still has the means to limit the damage it has caused – as long as there is hope, there is life!
Why should seagrass beds also be preserved?
These are underwater plants, not algae, which capture about 5 times more CO2 than a terrestrial forest. And seagrasses, threatened, have two major allies, two animals, two predators. Otters, first, which feed on sea urchins, which proliferate without predators and which decimate these meadows… By digging into the vegetation, otters also promote the production of seeds and their germination.
As for the tiger sharks, we noticed in Australia that they frightened the turtles, which had to find other refuges. Without tiger sharks, seagrasses would be on the verge of extinction. But the sharks themselves are threatened with extinction.
#hot #marine #biodiversity