Climate and shipping: how the Mediterranean is invaded by alien species

Stressing the importance of research and monitoring is Ernesto Azzurro, a researcher at the CNR, also in the light of the sightings recorded especially in the Ionian Sea. "The observation of a new tropical species may arouse curiosity, but it is actually only the tip of the iceberg of a profound upheaval in marine biodiversity," he says. "The Mediterranean, as we have known it, is disappearing. Species no longer adapted to the new climatic conditions are rapidly regressing, and among them many that for millennia have represented our nourishment, our culture and our traditions. This process is leading to the formation of new ecosystems, with profoundly different and as yet largely unknown ecological arrangements.

So the causes 'depend on multiple factors'. "In particular, as far as biological invasions are concerned, it is crucial to remember that alien species must first be introduced into a new environment, a process that by definition takes place thanks to human activities,' he adds. 'Think, for example, of the opening of the Suez Canal in 1869, which created a direct corridor between the Red Sea and the Mediterranean, or the numerous vectors, such as ships' ballast water. It is very important to be able to recognise these new species, also to prevent potential risks such as poisonous spines or toxic meat'. In this scenario there is the role of citizens who 'can make a fundamental contribution to monitoring biological invasions, simply by reporting their observations to the scientific community'.

Quite complicated then, as is the case on land, to proceed with eradication since 'the vastness of the sea makes this impossible'. 'It would be desirable for all of us, as citizens, to become more aware of the extent of these changes,' he concludes. 'Only in this way will we be able to make our voice heard by the political class. It will not be possible to reverse the course, or even slow down the phenomenon, if we are not able to question a development model that continues not to care about planetary limits and to act as if we lived on an infinite planet'.

The changing Mediterranean does not only affect the waters. In Spain's Mediterranean regions, climate change is also manifesting itself on land: increasingly intense heat waves and water stress are putting Mediterranean forests - made up of holm oaks, cork oaks and pine trees - in crisis and causing increasingly frequent fires.

According to the Pyrenean Climate Change Observatory, alterations in the life cycles of animals and plants are leading to phenomena such as migration to higher latitudes and altitudes, desynchronisation between species (e.g. between pollinators and plants), and the expansion of pests such as the pine processionary moth.

Spain's seas are also warming: the rising temperature is jeopardising delicate ecosystems such as posidonia meadows, which are essential for biodiversity and coastal protection. Native fish populations are decreasing and tropical ones are increasing, including exotic fish and invasive jellyfish.

In recent years, there have also been mass deaths of corals and gorgonians, and a colonisation of the Balearic Sea by exotic species. Between 2019 and 2023, 11 Caretta caretta turtle nests were identified on Balearic beaches: an unprecedented event that experts attribute directly to global warming.

In response, Spain has extended its network of marine protected areas and participates in programmes to monitor biodiversity and control invasive species. But the urgency for structural interventions remains high.

*This article is part of the European collaborative journalism project "Pulse"