A Changing Mediterranean Warming Mediterranean seas: native invasions and new alien arrivals
The Mediterranean Sea is warming quickly, with more frequent and intense marine heatwaves reshaping habitats and species’ ranges. However, not all species that become problematic in a changing ecosystem are alien; native species can also become invasive.
A species is considered alien when it is introduced outside its natural range, whereas the term invasive refers to a species that spreads and causes significant negative impacts to biodiversity, whether alien or not.
The bearded fireworm (Hermodice carunculata), is a good example. Native to the Mediterranean, it is a warm-water species whose distribution has expanded into areas where it was previously uncommon; when in high numbers heavily feeding on corals, anemones and echinoderms and altering rocky bottom communities.
Simultaneously, the Mediterranean is also receiving new species, particularly from tropical and subtropical regions through the Suez Canal, a major pathway for their arrival, which connects the Red Sea with the Mediterranean. Species that naturally move through the canal and subsequently establish and spread in Mediterranean waters are known as Lessepsian migrants.
Lessepsian migrants such as the lionfish (Pterois miles), the silver-cheeked toadfish (Lagocephalus sceleratus), and rabbitfishes (Siganus spp.) thrive as rising temperatures create suitable conditions; some pose health risks because of venomous spines or tetrodotoxin, a powerful neurotoxin that is not destroyed by cooking.
These examples illustrate two sides of a Mediterranean in transition: climate change can modify the behaviour and distribution of native or long-standing species and facilitate the establishment of new alien taxa.
Citizen science can also play an important role in monitoring these changes. As more people explore the Mediterranean by snorkelling, diving or walking along the coast, they can contribute to monitoring marine biodiversity by reporting unusual or unfamiliar species. Such observations can provide valuable information to researchers, helping them track changes in species distribution and detect new arrivals at an early stage.
In the photo: Top left the silver-cheeked toadfish (Lagocephalus sceleratus), bottom left the bearded fireworm (Hermodice carunculata), top right the rabbitfish (Siganus luridus), bottom right the lionfish (Pterois miles)