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The sea urchin, a new ally in the fight to stop the invasion of Asian seaweed on the beaches of southern Spain
Environment

The sea urchin, a new ally in the fight to stop the invasion of Asian seaweed on the beaches of southern Spain

This highly prized delicacy and endangered species has included Rugulopteryx okamurae in its diet

La Voz

Cadiz

Wednesday, 24 April 2024, 23:15

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Asian seaweed, Rugulopteryx okamurae, is one of the biggest headaches for this province. The invasion has ended up shrouding not only the beaches, but also the seabed, even causing the extinction of some species native to the Cadiz coastline. A huge blow to the fishing and tourism industries and as much an environmental as an economic disaster.

The fight against the invasion of this seaweed has as an ally in a much-depleted species, the sea urchin, a big consumer of seaweed. A ban on catching sea urchins has been in place since last October covering the entire Andalusian coastline due to the risk of it disappearing thanks to abusive fishing practices (as happened with sea anemones).

Sea urchins (erizos de mar) are edible and easy to catch as they live in the shallows - two factors that have led to overfishing by humans, with their capture reaching a peak right before carnival season and celebrated with their own festival known as the Erizada. Now, the sea urchins have to come from other fishing grounds, either Galicia or mostly Morocco.

A group from the Institute for Agricultural, Fisheries and Food Research and Training (IFAPA) is investigating to what extent the sea urchin would be able to mitigate the invasion were there a population recovery.

One of the researchers, Ismael Hachero, confirmed to the media that Rugulopteryx okamurae is indeed part of the sea urchin's diet.

The researchers have been following this line of research since 2021, first in saltwater pools where they found sea urchins surviving on a diet of this macroalgae from Asia. Next they collected samples from Sotogrande's coastline (in Cadiz province) where the seaweed has been present since 2016, La Herradura (since 2019) and Almería (from 2022).

"After dissecting the stomachs and using various genetic techniques, we found that it [the sea urchin] consumes this algae in the natural environment, with no preference for or against it, it eats whatever's available and in the same proportion," says Hachero from IFAPA, who is working with researchers from the Institute of Marine Sciences and the universities of Cadiz and Almeria.

Another line of research under development for this year is to find out whether an herbivorous fish, the salema porgy (Sarpa salpa - also known as dreamfish or cow bream), is also eating the Asian seaweed, and from there they will assess what further actions to take.

These Andalusian researchers also aim to study what to do with the algal blooms deposited on beaches.

Their key conclusion is to use it as a fertiliser for industrial greenhouses after mixing it with other plant waste from the land. The work of researcher Mariluz Segura, from IFAPA in La Mojonera (Almeria), has proven that it is nutritious having tested it last year on courgette and cucumber crops.

José Carlos García Gómez pointed out that this macroalgae, which is now showing up the Azores and the Canaries, was first detected in the Mediterranean in 2002, specifically in the Gulf of Marseilles, having been introduced to the waters there through aquaculture farming of the Japanese oyster.

Sea urchins on the critically endangered list

The "critical situation" of the sea urchin, according to the Ministry of Agriculture and Fisheries, led to the closure of all fishing grounds located very close to low tide markers.

At that time there were 14 licences in Andalucía for catching sea urchins as well as the sea anemone known as ortiguilla. To be precise, there were six in Granada, four in Malaga and four in Cadiz, each of which permitted catches of 30 kilos per day of sea urchins (Paracentrotus lividus) between November and April.

As stated by the Junta when the order was issued, the eating of sea urchins is a traditional practice in towns in Cadiz province, but "it has been spreading to the other provinces and other regions of Spain, such as Galicia", which has caused a progressive increase in catches, in almost all cases done illegally.

Overfishing is compounded by two other factors: the continuing rise in seawater temperatures, which has affected numerous invertebrate species, and the arrival of the Asian seaweed, the now infamous Rugulopteryx okamurae.

This plant has taken up residence on the rocks where sea urchin larvae once settled, but when the sea urchins disappeared, the algae took over, explained Prof José Carlos García Gómez, marine ecologist at the University of Seville.

When it appeared in 2015 in Andalucía "it was a real I came, I saw, I conquered moment", he said, simply because the waters are much warmer than in other areas.

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