The Balearic Islands welcome an invasive plant that until now was impossible in its waters

In October 2023, a group of divers were fully immersed in the Bay of La Palma when they found something that should not be there: a tropical marine plant rooted in the bed, where we usually find either sandy bottoms or Posidonia meadows. The notice from the Balearic Center for Applied Biology was confirmed through dives by the CSIC-UIB and CEAB-CSIC teams and the discovery was published in Mediterranean Marine Science.

The presentations. The name of tropical marine plant is Halophila stipulacea and it is a seagrass and not an algae (unlike algae, it has roots, stems and leaves), much smaller than the native Posidonia Oceanica, with which it now shares spaces.

And although it has appeared about 3 kilometers from the port of Palma, on a sandy bottom, it is foreign: its origin comes from the Indian Ocean, Red Sea and the Persian Gulf, although as a good tropical came to the Caribbean. The opening of the Suez Canal in 1869 was its one-way ticket to the Mediterranean, however in these 150 years its expansion was only recorded in the eastern area, never as far west as the Balearic Islands. It is already a total colonization.

Context. The waters of the Mediterranean Sea are warming more than the global average: between 1982 and 2019, its surface temperature increased by 1.3 °C compared to a global average of 0.6 °C, according to MedECC data. In summer, the temperatures of the Mediterranean Sea recorded in the Balearic Islands They are around 30 °C.

This point is important because it marks a milestone: the conditions of the Mediterranean are changing. That is, Halophila may have reached this far west before, but it did not have favorable conditions to survive and now it does. As explains Andrés Arona, first author of the study and Imedea researcher, is “a clear indication of the ‘tropicalization’ of the Mediterranean.”

Why is it important. To begin with, because Halophila Stipulacea acts as a biological thermometer of real change in the Mediterranean. A tropicalization that opens the doors to some species and closes them to otherslike Posidonia or corals. But it also matters because the worrying precedent of the Caribbeanwhere its rapid colonization of large areas reduced biodiversity, altering the ecosystem. Something that is already happening in the eastern Mediterranean.

Potential environmental impact. Given its presence in degraded sandy bottoms, its effect is ambivalent: it can increase structural complexity, although it can also displace the fauna typical of these bottoms. The greatest risk, however, would be if it came to compete with native phanerogams such as Posidonia oceanicasomething it has already done with other species in the Caribbean, where it colonized large areas in less than 20 years.

The difference between both plants is not trivial. in words from Imedea researcher, Fiona Tomàs, “Posidonia is like a sequoia, Halophila is much smaller”: Posidonia generates a structural complexity that supports breeding habitats for hundreds of species and accumulates carbon in another order of magnitude. Halophila It does not generate anywhere near that architecture or that carbon storage. A change in species dominance would profoundly alter the ecosystem.

What can be done. The good news is that this detection has been early and the sooner the warning comes, the more room there is to take action. The not so good thing is that it is a plant with its seeds and that the most definitive thing would be for the Mediterranean to reverse its tropicalization, but that means stopping the global warming. Little joke.

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Cover | Benjamin Guichard and Mariya Oliynyk