The ‘tropicalization’ of the Mare Nostrum advances due to its warming and international ship traffic
The Mediterranean is the most invaded sea on the planet. There are more than 1,000 exotic species, that is, from other ecosystemswhich in recent decades have found their new home in this basin, according to the report The effect of climate change in the Mediterranean Produced by the World Wildlife Fund (WWF).
This is the consequence of a compendium of factors that come together in the Mare Nostrum and that go from the effects of climate change to the intense maritime trade of this geostrategic zonea, for being a union of three continents. The natural physiognomy of this closed sea also influences. All this is contributing to the proliferation of exotic animal and plant species, while increasing the threat to endemic Mediterranean ones.
The Mediterranean Sea is heating up and it is doing so faster and faster. Specifically, that temperature increase occurs 20% faster than the global average and is already one and a half degrees higher than the average for pre-industrial times (1880), according to the report Risks associated with climate change and environmental changes in the Mediterranean region, produced by the MedECC network.
Likewise, researchers from the Mediterranean Climate Change Group of the Spanish Institute of Oceanography (IEO) together with experts from the Balearic Islands Coastal Observation System (SOCIB) and the Barcelona Institute of Marine Sciences (ICM-CSIC) add another piece of information: that temperature increase is solidly placed at two degrees per centuryas concluded in a study published in the journal Frontiers in Marine Science.
Thus, the Mediterranean is moving towards its tropicalization and is becoming more and more a comfortable area for new species of warm waters, but less welcoming for those that need colder waters, which move towards more northerly latitudes.
This is what the researcher at the Institute of Marine Sciences-CSIC, Pere Abelló, qualifies as “natural movements” of species, which have occurred since the first ice ages and which now continue with the imbalances of climate change, increasing the presence of species exotic species and the displacement of autochthonous and endemic species.
“If a species likes cold water and the water gets warmer, what it does is go north in a natural way. They are looking for their optimal temperature. This is a reality that we are observing, especially in recent decades », he explains.
closed sea
However, in the case of the Mediterranean, being a semi-enclosed sea, connected to the Atlantic by the Strait of Gibraltar and to the Black Sea by the Bosphorus Strait, native marine species have little room to find new locations, so if they are unable to adapt, their survival is threatened. «The cold-water species, if they go up north, meet the coasts of France or Italy. Either they adapt, or they die of heat. Meanwhile, African species can enter through the Strait of Gibraltar”, continues Abelló.
“They could also migrate deeper, but there are species that need light, such as all plant species, algae, seagrasses or even some corals, since the depth they can reach is limited by the light that reaches them. That it is a closed sea has consequences, especially for native species, ”adds Núria Marba, researcher at the Mediterranean Institute for Advanced Studies (IMEDEA-CSIC).
Suez Canal
In 1869, the Suez Canal was inaugurated, a 163-kilometer artificial route that connects the Mediterranean Sea with the Red Sea. After two centuries, this route has become a key element for international trade, since it allows the connection between Europe and Southeast Asia without having to go around Africa.
Beyond the commercial achievements, the construction of this channel also meant the opening of the largest gateway for species from the Red Sea and the Indian Ocean that now live in the Mediterranean. An example of this is the rabbit fish, a species of subtropical origin that is green, light brown and yellow in color and has poisonous spines on its dorsal fins.
«These species normally stayed in the area of Egypt, Israel, Turkey, Greece… very hot waters, but they did not reach the western Mediterranean area. What happens is that as the waters of the Mediterranean have been warming up quite a bit, especially during the last decades, clearly due to the effect of climate changethe species that have been established in the Eastern Mediterranean for more than a century have already arrived, or are arriving,” adds Abelló.
ballast water
Another of the most effective ways for the introduction of invaders in the Mediterranean is ballast water, used to ensure the stability of ships carrying merchandiseyes Thus, ships flood tanks installed inside the hull in a controlled manner, which are loaded and unloaded as needed.
“In salty and warm waters, the boat floats more, it needs to take in more water to maintain its stability and, at the same time, in cold waters it needs to release water,” says the researcher.
Due to the globalized commercial structure, it may happen that a ship loads its ballast water tanks in Florida and unloads them, for example, near the Spanish or Greek coasts, which generates an excellent international distribution system for larvae and small organisms. .
Fish, crabs and algae: the new hosts
The Caulerpa cylindracea, a green algae endemic to southwestern Australia that is believed to have been introduced through shipping and aquaria, the hobby of fish farming.
According to the International Union for Conservation of Nature (IUCN), it is one of the 100 worst invasive species in the Mediterranean, since it is capable of altering the physical and chemical conditions of the natural environment.
In the same way, the Lophocladia lallemandiia stringy red algaeis displacing the Posidonia oceanicaa fundamental species in the face of climate change, since it acts as a store of carbon dioxide.
However, not all exotic species have negative effects on the ecosystems where they are introduced. It is the case of the Halophila stipulacea, which contributes to the sequestration of CO2 in the Mediterranean. That was the conclusion of an international study in which IMEDEA (CSIC-UIB) participated, which analyzed the effects of this plant species from the Red Sea and the Indian Ocean, which was introduced through the Suez Canal and has colonized the eastern and central Mediterranean coast.
“The halophila it is a very small herb that grows where native herbs have disappeared or where there were no herbs before”, explains Núria Marba, a researcher at the Mediterranean Institute for Advanced Studies (IMEDEA-CSIC).
“What we have seen is that they are important in burying carbon. It can generate carbon sinks just like the other seagrasses we have in the Mediterranean, such as Posidonia.”
As for the exotic animal species found in the Mediterranean, two stand out. The Lion fish It is characterized by its conspicuous white and red streaks and its fins with poisonous spines. It comes from the Indo-Pacific. «It is a voracious predator, it is very similar to the scorpion fish we have here. It is causing problems in Greece and Turkey,” says Pere Abelló.
Another exotic is rabbit fish, also poisonous, with shades ranging from brown to greenish gray, and light brown to yellow on the belly. Its origin lies in the Red Sea and the Indian Ocean.
It has very poisonous spines that can be lethal, which is why it poses a risk for sport fishing and a handicap for tourism in coastal areas.
“If a fisherman catches it, it cannot be marketed. You have to be careful”, warns the researcher from the Institute of Marine Sciences.
In the case of crustaceans, Abelló points to the american blue crabfrom the coasts of North and Central America (to a lesser extent also present in Brazil) as one of the species that is causing the most problems.
In the Western Mediterranean, they have already been detected in the Mar Menor de Murcia, although without major effects, and in the Ebro Delta, where significant populations were created.
“It is a species that is trying to be mitigated through fishing extraction. It is found in areas of brackish water, also in fresh water upriver, although normally in areas that have a certain salinity”, explains the researcher. “It has a very complex reproductive cycle and a very high fertility rate that makes it a difficult species to eradicate.”