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Managing the growing number of non-Indigenous species in the Mediterranean Sea

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Managing the growing number of non-Indigenous species in the Mediterranean Sea
Copyright  Euronews
By Denis Loctier

Hundreds of non-Indigenous species have invaded the Mediterranean Sea over the past few decades. 

Today, they are altering local biodiversity, disrupting fisheries and aquaculture throughout the region. But some of these invasive species are generating commercial opportunities for the fishing and aquaculture sector. 

The rise of the Blue Crab

The Ebro Delta is Catalonia's largest wetland, home to hundreds of aquatic species and a place with a long fishing tradition. 

For centuries, the local association - 'Brotherhood of San Pere' - has been fishing in the largest lagoon, the Encanyissada. But a few years ago, their usual catch suddenly dropped. Instead, they found a surprising newcomer: the blue crab, a ferocious North American crustacean that has invaded the area, decimating local species.

"What happens is that it eats all the young species, it eats all the eggs, and destroys our nets! It eats everything! It ate all the endemic fish here," explains local fisherman Raul Paulino.

With other species largely gone, local fishermen switched to catching the blue crab.

"In the first few years, they were abundant but weren't highly-priced. Now it's the opposite - fewer but worth more. But hey, that's the fisherman's life," Raul says. 

Local researchers say allowing professional fishing of these new crabs is the best hope of stopping an explosion in the population.

Catalonia has put in place a special co-management committee with the aim of providing better scientific advice, improving the capture and streamlining blue crab trade through the fishing market. 

This part of Spain is being closely watched by other regions, increasingly affected by the blue crab invasion. 

The General Fisheries Commission for the Mediterranean has launched a regional research programme on blue crab propagation across the Mediterranean Sea. 

"We need to solve problems with the knowledge. And this knowledge comes from all parties involved in the problem — that is fishermen, fisheries administration and also scientists, but also NGOs," Pere Abelló, Senior researcher in crustacean biology, ICM-CSIC, says. 

Some reasons to be cheerful

Innovative technology and Catalonia’s large-scale fishing infrastructure appear to have had an impact: its blue crab population has apparently stopped growing, though more studies are needed.

In any case, the invasive blue crab, likely brought from America in the ballast waters of commercial ships, is here to stay.

"For now it must be said that eradication of this species is virtually impossible due to its inherent characteristics. But our goal is to be able to control the population to minimum levels, to allow the other species to recover, and thus allow fishermen to once again take advantage of all the resources they once had," says fishery biologist Verónica López.

A major positive is that the blue crab tastes great, so fishing the species intensively is a win-win for the environment, the fishing sector and consumers.

Restaurateurs like Albert Guzmán have embraced the North American invader as a local delicacy.

The Atlantic blue crab might seem unfamiliar to Mediterranean cuisine, but the chef says it fits in perfectly with other seafood, served either as the main dish or in broths, snacks, appetizers, sauces and paellas.

"We used to use different, much more expensive species, such as lobsters or the spider crab, which is not native — it had to be delivered from Galicia. And now we have the blue crab which has a similar flavour and taste - so we have a great, top quality product at a price that is suitable for affordable restaurants, which is also a good thing," says Guzmán. 

Not just a Catalonian problem

But invasive species aren't just in Catalonia. In Greece, in the Gulf of Elefsina west of Athens, local fisherman Giórgos Grívasregularly gathers non-Indigenous bivalve molluscs. Originally from the Indo-Pacific region, they spread to this part of the Mediterranean through the Suez Canal - one of the primary pathways for non-Indigenous marine species into the Mediterranean.

"This is the so-called pearl oyster, Pinktada imbricata radiata. In addition to the food, we sometimes find pearls. It can be consumed raw, baked, steamed or fried, in pasta or risotto," Giórgos says. 

The fishermen sell the pearl oysters to local fishmongers who then sell them for €5 per kilo - but the trade is constrained by a lack of regulation.

Unlike mussels and other popular local molluscs, pearl oysters are considered an exotic species, and Greek legislation doesn't cover their exploitation for human consumption.

John Theodorou, an Associate professor at the University of Patras is working to change that. His research calls for the legalisation of pearl oyster fishing in Greece so that they can be fished sustainably and sold for higher added value.

"It’s very important because it offers an alternative for the fishermen to improve their income as the pressure on the natural stocks of other shellfish increases due to overfishing and climate change, he says. 

"Pearl Oysters a superfood"

Researchers at the University of Patras have concluded that pearl oysters don't harm endemic species and can be fished sustainably.

They have drawn up new rules and standards for the whole value chain - from fishing specifications to best storage and transportation practices.

Recipes with pearl oysters are already being studied at cooking schools in Greece.

Eleni Liakea, a professor of tourism and hospitality told Euronews: "People like this meal immensely! I would even call pearl oysters a superfood, they are rich in proteins with minimal carbohydrates and fat, and they have a lot of flavour and a delicious taste."

Pushing for regulatory change

Legalisation could be good for aquaculture too. In Sagiada, near the Albanian border in western Greece, Spyros and his father grow shellfish on submerged ropes.

The only invasive species that gives them trouble is the translucent ascidians that need to be constantly cleaned off the ropes. But the farmers don't mind the pearl oysters, occasionally found among their main harvest. 

They say this could be another product to sell if the regulatory framework accounted for this non-Indigenous species.

"We can't grow them legally, nor sell them. So we just basically gather them for our own consumption, whenever we have parties or whenever special people come," said Spyros Stasinos, from Stasinos Mussel & Oyster Farm.

The aquaculture sector is expanding rapidly in this part of Greece. Mussels and oysters help keep the water clean from excessive nutrients. They are also a great healthy food source, so the cultivation of pearl oysters could be a harmonious fit.

"It grows fast, it tastes good, the markets are present. So I think it's a matter of time to commercialise this new resource. We cannot eradicate this species. We have to co-evolve with them as a society and as a production sector," explains Costas Perdikaris, the head of the Epirus Regional Fisheries Department. 

The invasion of hundreds of non-Indigenous species in the Mediterranean Sea over the past few decades is a major challenge – but also an opportunity for the fishing sector to adjust and make the most of it.