At a fish shop in the village of Aspra, near Palermo, the capital of Sicily, the day’s catch is decorated with green paint. But rather than being an ingredient to be cooked as a side dish, it is the local fishermen’s worst enemy. known as Rugulopteryx okamuraeThis invasive seaweed has become the bane of their lives. For the past two years they have been spending several days trying to untangle it from their webs, and have seen their income suffer as a result.
This problem is well known among their fellow fishermen in Spanish waters. “We’ve had algae here for 10 years,” says Gregorio Linde, captain of a small-scale fishing boat in Tarifa on the Strait of Gibraltar. “The sea floor is a carpet, and the nets catch nothing.”
His family has lived on the fruits of the sea for generations, but now his day is often spent hauling up seaweed – just to throw it back. And he is not alone. Losses from such small-scale fisheries in Spain exceed €3 million ($3.48 million) annually.
And it’s also hurting coastal tourism in countries like Spain and Italy, where vacationers sometimes scrunch their noses through foul-smelling mats of algae on white-sand beaches. Despite the effort and cost of taking it to landfill, new tides refill the beaches.
However, the biggest damage is out of sight. Underwater, seaweed is destroying vital seagrass beds, harming sea urchins and taking over fish habitats.
“The socioeconomic impacts can be compensated for with money, but this unprecedented ecological impact cannot be compensated for,” warns Maria Altamirano, a researcher at the University of Málaga who first identified the algae in Spain. The “invasion”, she says, “is like a wildfire in a national park: everything is destroyed, and only one species is left.”
The Mediterranean Sea: a hotspot for non-native species invasions
Although it covers less than 1% of the world’s maritime area, the Mediterranean Sea hosts almost a quarter of global maritime traffic. And that, according to the European Environment Agency, is responsible for half of all non-native species introduced into the ocean since 1970.
According to Luca Castriotta, an invasive species expert at Palermo’s National Institute for Environmental Protection and Research, more than half of all non-native species found in European waters live in this semi-enclosed sea. He says one in 10 becomes invasive, displacing native marine life and reshaping ecosystems.
Rugulopteryx okamuraHe is a big criminal. It is native to the Pacific region, where it lives in balance with ecosystems in Japan, China, Taiwan, Korea, and the Philippines. The species was first identified as invasive in 2015 in Ceuta, a Spanish enclave on the North African coast along the Strait of Gibraltar.
Encouraged by overfishing and pollution – which weakens ecosystems – as well as warm waters and the absence of natural predators, its aggressive progress didn’t stop there. Since then it has spread to different parts of the Mediterranean Sea and reached Atlantic archipelagos such as the Canary Islands, the Azores and Madeira. In 2022, it became the first algae on the EU’s list of concerned alien species.
How ballast water balances ships and unbalances the sea
Scientists believe the seaweed reached the Mediterranean Sea via ballast water left by cargo ships traveling between Asia and Europe. Before leaving port, ships pump water into their internal tanks to stabilize the cargo. They then expel it at its destination – along with any hidden spores, larvae or eggs.
“Today the world is interconnected. For example, we buy products in China, which are distributed all over the planet. But along with the goods we want, we are also transporting species from one place to another,” explains María García of the Spanish National Research Council (CSIC). She has been monitoring invasive species in the Mediterranean’s coastal waters for 30 years and says the trade is “completely aging out” its fauna and flora.
In 2004, the International Maritime Organization (IMO) adopted a convention requiring ships to treat ballast water – although it only went into effect in 2017. And since September last year, ships flying the flag of a signatory country or discharging ballast in its ports must install onboard treatment systems that prevent anything except tiny particles – 10 microns – from being discharged.
Experts call it a step forward, but enforcement remains weak. Garcia admits, “Efforts have been going on for years, but compliance is difficult because of the cost. It often depends on the goodwill of shipowners and crew.”
Checks rarely take precedence over other port priorities such as ship security. Authorities in countries like Spain are short of funds. Other countries, such as Italy, have not ratified the IMO Convention, meaning foreign ships can legally discharge untreated ballast water into the country’s ports.
“We cannot interfere directly with private individuals, because that would conflict with economic activity,” Castriota says. “Until the IMO Convention is ratified, our hands are tied.”
Citizen science: an ally against the tide
Once a species is established, it becomes necessary to slow the spread. “We know that algae can thrive in a much larger area than at present. We must prevent it from getting there,” Altamirano stressed.
Strong ballast water controls and cooperation with fishermen and recreational boat owners are important, as nets and hulls often carry algae. But civic engagement also matters.
It was a citizen science platform that first flagged the arrival of Asian algae in Murcia in southeastern Spain. And García’s team collaborates with more than 5,000 volunteers in the northern Catalonia region, which is also affected. They upload photos of suspected invasive species to the Observadores del Mar platform. “We scientists work in our laboratories, but there are huge areas of the ocean that we can’t cover,” Garcia says.
But preventing future attacks will take more than dawn sails and laboratory experiments.
Altamirano says this requires international coordination, dialogue between science and policy makers and affected areas, and active citizen participation.
,Rugulopteryx okamurae It’s one of many invasive species,” she adds. “We definitely need to get the machinery running smoothly for the next species to come in.”
Edited by: Tamsin Walker
This reporting was supported in this story JournalismFund Europe.