Estepona fishing boat takes part in research on effects of invasive Asian seaweed on the industry

It is 4am on 29 June and the 'Jaime and Sara' fishing boat belonging to brothers José Antonio and Eduardo Peña is ready to go to sea to fish, departing from the port of Estepona on the Costa del Sol. Also with them is a doctor in biology David León - a member of the Asociación Hombre y Territorio.

For the last year, the boat has been serving research purposes thanks to the efforts by Estepona's fishermen guild. Like all boats in the area, it is suffering the effects of the invasive Asian algae (seaweed), which has made these research actions vital for the fishing sector.

The red mullet is the most affected by algae fish, as it has always fed on the green growth on rocks. That green growth has gradually been overtaken by the "weed," as local fishermen from Estepona call it. The algae first appeared in the area in 2016, detected in the Strait of Gibraltar, near Tarifa, and instead of disappearing, it has continued to spread. "This area around Estepona and Manilva has been the most impacted by the algae ever since, nearly ten years now," says David León.

Eduardo Peña is 46 years old, but he has been fishing since he was 13. Coming from a family of fishermen from Caleta de Vélez-Torre del Mar, he says that life at sea is "very hard - there is no fixed salary, you earn as you fish, some days more, some days less, but it's getting worse now". The invasive species is largely to blame.

Eduardo showed SUR's team a video, which shows how the seaweed gets caught in all his trammel nets, used for a fishing method that he knows well but finds increasingly difficult to maintain. "We throw the net into the sea with buoys and stones and haul it in. For mullet fishing, the net stays in the water for an hour and then rises like this," he says. Dozens of invasive algae get entangled in the net, moving with the currents and invading everything. This makes the net visible to the fish, which decreases the success rate of the activity.

"You don't earn a penny and you get fed up with working. The trammel net is lost with this. There are places we can't even go near because of the amount of seaweed there is," says Eduardo.

David León adds: "The impact of the algae on the fishing sector is enormous, starting with the time spent cleaning the net. The algae pulls the net down from its natural position, makes it visible to the fish and there is no fishing. The seaweed also takes up a lot of space on the seabed, on the shoreline and throughout the water column, choking the shellfish and pushing other species out."

"No species feeds on it, it is very difficult to eliminate," says León, highlighting the nature of the Asian algae as "uncontrollable". He adds that "it has already been found even on the Galician coast; it adapts to little light, little oxygen, to areas with more salinity, with less, it has no predators, it goes unnoticed with other species".

The solutions for the fishermen include changing fishing areas, in which Eduardo is already an expert, and changing certain aspects of the fishing gear.

Ruguplas project

There is a ban on the manipulation and exploitation of algae for commercial use due to its invasive nature. However, the Asociación Hombre y Territorio and the Instituto Tecnológico del Plástico (AIMPLAS), with the collaboration of the fishermen's guilds of Estepona, Sanlúcar de Barrameda (Cadiz) and Gandía (Valencia), are carrying out research to see what uses it could have.

The project is called Ruguplas. Its first phase, which ends in January 2026, aims to obtain bioplastics derived from it for use by the fishing sector in areas where the algae is already established.

"Algae are already used in the textile industry or cosmetics and alternative uses are being sought as fertilisers or as insulation for roads. We are studying the feasibility of using it to make bioplastics, in order to remove it from the environment and help reduce plastics and marine litter," says David León. "I go on board with Eduardo every term, I see how he works, we take samples from the sea, I learn a lot with him, while my colleague Bárbara Conejero collects samples of the seaweed that ends up on the beach." The samples are then analysed at the institute of plastics.

The second phase of the research will begin in January 2026 and the Peña brothers' ship will continue to be a useful vessel, because the sea is their life and they want to protect it.