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Marine Science


New arrivals in an ancient sea

New arrivals in an ancient sea

The Mediterranean is changing fast. Over the last few decades, its waters have seen the appearance of unprecedented numbers of new fish, crustaceans, plants and other forms of life, so-called non-indigenous species (NIS).  The new arrivals are competing with native marine life and causing major ecological and economic impacts, and the scale of the issue is revealed in a ground-breaking new scientific study from the General Fisheries Commission for the Mediterranean (GFCM) of the Food and Agriculture Organisation of the United Nations (FAO).

GFCM researchers have catalogued more than 900 NIS in the Mediterranean; over half of which have now established permanent populations and are continuing to expand their ranges.

How and why is this occurring? Most NIS have migrated from the Indian Ocean and Red Sea through the Suez Canal. Climate change is happening 20 percent faster in the Mediterranean than the global average, and the fast-warming waters of the basin, particularly in the south and east, are now temperate enough to support many tropical species.

Other NIS – algae, clams, barnacles and the like – hitch a ride in fouling on ships’ hulls, with small fish sometimes hiding among them. Meanwhile ballast water pumped into ships to stabilise them when they’re not carrying cargo is pumped back out when they reach their Mediterranean destinations, along with alien plankton, spores and eggs, which sometimes go on to thrive in their new home.

NIS can also be moved by humans. Mosquito fish were introduced into Black Sea wetlands to eat mosquito larvae and eggs in an attempt to combat malaria, and now they’ve become abundant across the Black Sea basin. Foreign species imported for aquaculture sometimes escape into the local environment – the Pacific oyster, for example, now outcompetes its native Mediterranean relatives.

NIS can have very serious impacts on native biodiversity – and the livelihoods that depend on it. They compete for food and habitats, in some cases displacing native species almost entirely. The rabbitfish is a notorious example, monopolising food supplies in Turkish waters and swiftly transforming complex algal forests into rocky barrens; while the voracious lionfish – first caught in a trawl in Israel in 1991 but now spreading widely across the basin – is judged by some to be the single most damaging invasive species known to science.

Non-indigenous jellyfish numbers have exploded since the 1980s, and they’re thriving in the warming waters. They’re now eating so many fish eggs and larvae that commercial catches of small pelagic fish have dropped significantly. Jellyfish of all kinds are clogging fishers’ nets and tourist beaches alike, causing serious economic problems in many countries.

But NIS sometimes offer economic potential too. The rapa whelk originated in the western Pacific and was first observed in the Black Sea in 1947, where it had a detrimental impact on native oysters and mussels. But enterprising locals began to harvest the invasive snail, and today it supports a lucrative Asian export market. Last year, the GFCM launched a scientific survey-at-sea of the specie, as a benchmark for future cooperative efforts to assess similar situations.

“Countries of the Black Sea are performing, for the first time, a sea research survey at the same time with the same methodology throughout the Black Sea,” said Dr Elisabetta Betulla Morello, GFCM Fishery resources officer. “We are hoping to extend this synergy to other key species and create shared memory in the Black sea and the Mediterranean.” 

The economic potential of lizardfish, goatfish and various mackerels is also highlighted in the GFCM report; along with crustaceans including several species of prawn and swimming crab. Blue crab are a good example: first found off Tunisia in 1993, by 2014 they were causing significant harm to small-scale fisheries, damaging gear, feeding on fish caught in traps, and outcompeting other species for food. “Blue crabs eat everything, leave nothing and reproduce very quickly,” lamented Mouradh, a fisherman from the Tunisian islands of Kerkennah. But the crabs themselves are good to eat, and local fishers began to target them. In May this year more than 2,000 tonnes were harvested, worth over $7 million. Private sector investment is expanding markets around the world.

Via its technical unit in Malaga, dedicated to the Western Mediterranean, the GFCM is supporting governments and fishers in the region with a research programme and stock assessment of the two species of crabs that entered the Mediterranean Sea: the blue swimming crab (Portunus segnis) and the American blue crab (Callinectes sapidus).

This research programme, involving all Mediterranean countries, will monitor the dispersion of these species along coastlines as well as determine their impact on fishery resources and assess their income potential in countries throughout the region.

The ultimate goal in the near future is to create a regional observatory for NIS where data and best practices can be shared by fishers, managers, scientists, environmentalists, economists and others across the Mediterranean basin.

“Gathering reliable data on changes in distribution and abundance of NIS is essential for understanding and managing their impacts, as is spreading information and raising awareness,” says Pilar Hernandez, head of the GFCM Technical Unit for the Western Mediterranean. “We’re focused on learning a great deal more about these new arrivals so we can build capacity to manage the dangers they pose to native ecosystems, while exploring their potential as new commercial species that could benefit from proactive fisheries management.”

Learn more about Non-indigenous species in the Mediterranean and the Black Sea

New Arrivals in An Ancient Sea Source