cor beyond 17 thousand animal species and almost 25 thousand plants present, the Mediterranean Sea – which includes the Adriatic, Tyrrhenian and Ionian Seas – contains unique forms of life, typical of this area. As the monk seal, the white corals madrepora oculata and Lophelia pertusacapable of building real reefs on deep seabeds, or the ferrous limpet, a gastropod mollusc with a beautiful star-shaped shell.
Rising seas: difficult predictions
To dangerous factors such as anthropic pollution of all kinds, trawling, the immeasurable exploitation of fish and the effects of excessive or disrespectful tourism for the environment, plus the consequences of climate change, induced by human activity. The rains, floods and low temperatures of last May should not be misleading.
“It is difficult to formulate precise forecasts, but the general trend, beyond the variability between one season and another, is that of a hotter summer, as has happened in recent years” he comments Susanna Corti, climatologist and research manager all‘Isaac (Institute of Atmospheric and Climate Sciences) of the Cnr. To get an idea, the scholar invites us not to stop at a single season.
“We need to be aware that climate change is taking place, the effects of which are an increase in variability and extreme events,” he clarifies. «Periods of long drought could alternate with extremely rainy moments. It is necessary to act in time. Our area is very vulnerable, we need to think in terms of planning and prevention, and not just responding to emergencies» comments Corti.
It serves a dual action of adaptation of human activities and mitigation, to prevent the situation from worsening further. Italy has 7500 km of coastline, which in the last fifty years has often been subject to wild management, building where it shouldn’t have been. If the hydrogeological instability already existed, now it worsens with the presence of extreme phenomena.
A typical Mediterranean marine environment. Posidonia oceanica is the protagonist, a native plant which is however very negatively affected by climate change
Designing barriers to defend the seas like in Holland
Lands that collapse are unfortunately not the only problem. Do you remember the disaster film The Day After Tomorrow, released in 2004? In a chilling scene, a tidal wave engulfed Manhattan.
“It’s very unlikely, for now,” reassures Corti. “But let’s not forget that millions of people around the world live along the coasts. Sea level rise is a phenomenon that has already begun, more evident where the coast is lower. And it will continue, even if there is a lot of uncertainty about its speed. The cause is the melting of the glaciers, not only in our mountains, but in Greenland and in the Arctic, due to the increase in temperatures due to carbon dioxide. “If we do nothing, in 2100 the seas will rise by a meter,” he specifies.
“But even with zero CO2, they will still go up. The atmosphere is quicker to react, but the seas are slow once the process is triggered.” In an optimistic scenario, the level will rise by half a meter by 2100. In a more apocalyptic one, the growth will be 2 or 3 meters and more lands will be submerged. Even the Mediterranean would be involved, and it would no longer be a question of saving only Venice, but also other areas, for example, along the Adriatic coast. We need to start thinking about the future now, designing barriers like the ones existing in Holland for its territories below sea level.
Blue crab versus green crab
The atmospheric temperature is rising, it is now a fact. According to the UN World Meteorological Organization, we have a 66 percent probability that by 2027 we will exceed the threshold of 1.5 degrees of increase compared to the pre-industrial period. The waters of the Mediterranean are also warming up: by 2100, up to 3.5 degrees more are expected, according to the Soed 2020 report. The tropicalization of our seas is already underway. “New animal and vegetable species settle and their presence has effects on the whole marine system in terms of habitat and biodiversity» explains Alessandra Pugnetti, marine ecologist and researcher at Ismar (Institute of Sea Sciences) of the Cnr.
“In the Venice lagoon, a large presence of two brown algae is documented, sargasso and undaria, both non-native and originating from the eastern seas”. The vehicle of these migrations is always man. The water discharged from ships, or even the ships themselves, rather than imported shellfish, helps the algae to establish themselves. Then, the increase in water temperatures helps to favor its proliferation. This is also the case with some animals.
«For ten years I have been taking care of the blue crab (Callinectes sapidus) that arrived in the lagoons of the Gargano area» he says Lucrezia Cilenti, marine biologist and Irbim researcher (Institute for Biological Resources and Marine Biotechnology) of the Cnr. «The blue crab larvae have found a welcoming habitat. The population grows rapidly: each female produces from two to eight million eggs. They have reached as far as Venice and threaten the native, smaller green crab».
Can this invasion be contained? “We have worked on selective fishing of the females and on promoting the consumption of this crustacean, organizing show cooking: the pulp is tasty”. Higher water temperatures attract fish migrating from the Red Sea. «The barracuda, the spotted puffer fish, the rabbit fish have reached our seas» adds Cilenti.
A warmer sea, on the other hand, does not please the gorgonian, a wonderful red or yellow Mediterranean coral: it bleaches and dies.
Some plants will migrate north
“Long periods of drought with high temperatures or a flood alter the marine balance and affect all living organisms,” explains Pugnetti. «We imagine our sea as a three-dimensional environment, a column of water with many depths and different light conditions and densities, influenced by the temperature and by the flows of the rivers. It’s not static: there are reshuffles that happen naturally. An extreme event such as flooding does not only impact the temperature, but pours a quantity of water with pollutants, fertilizers and organic matter that change an already complex and non-uniform system. For example, a lagoon is different from the open sea».
In addition to causing the climate alterations that generate extreme phenomena, carbon dioxide is also responsible for the acidification of the oceans and the Mediterranean: a lower pH affects the capacity of corals, molluscs and crustaceans to accumulate carbonate, which serves their structures or shells. “The Mediterranean is a climatic hotspot,” adds Corti. «In the long term, the trend is one of overall drying up especially in the summer: it will rain less, and from a temperate region it will become more arid. Agriculture and flora will change.’
Many plants will migrate north. And we will have to take into account the salt wedge: when rivers run dry, salt water makes its way into estuaries and deltas, can seep into groundwater making water resources unusable for agriculture and further drying up the land. It is urgent to get to know these phenomena better in order to then act. Putting pressure, as citizens, on administrators and politicians. It’s not too late, as long as we move now. More and more, saving the Mediterranean also means saving ourselves.
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