Asian algae continue to invade the beaches of Cadiz: what was once a bothersome problem is now an out-and-out catastrophe

Cadiz. Miles and miles of beaches with fine white sand bathed by the sea. A paradise that nobody wants to miss. According to data from the Junta de Andalucía, 5.8 million tourists visited Cadiz in 2023. However, since 2015, the province has been facing an problem difficult to solve, at least until now: the appearance on many of its beaches of Asian algae, an invasive species of seaweed that is calling checkmate on the local authorities.

"The first time it was detected was in 2015 in Ceuta," said Prof Juan José Vergara from UCA (Cadiz University). From then on its growth has been unstoppable. Right now it is the beaches in the Campo de Gibraltar area and La Janda that are suffering the most. Nevertheless, the state of La Caleta beach in Cadiz city is increasingly worrying.

"In the last few days we have been in La Caleta and right now Asian algae (Rugulopteryx okamurae) is there. It has also become established; it is growing in the rockpools on the beach," said Vergara. Despite the fact that its spread along Cadiz city's coastline is increasing compared to previous years, "it still has not reached worrying levels in terms of it displacing local fauna and flora". This differs greatly with the situation in Tarifa and on beaches close to the Strait of Gibraltar where the effects of this invader are greater, both ecologically and socio-economically.

It has come to stay. The main hypothesis for its arrival in Spain is believed to have been via the ballast water from cargo ships arriving from Asia. "This does not mean that it came on a ship as a specimen. Moreover, the fact that it also resembled other species of seaweed meant that the arrival of this newbie went unnoticed by researchers," explained Vergara. Now listed in the Spanish catalogue of invasive, non-native species, Rugulopteryx okamurae grows in southern Spanish waters because of "the ideal conditions of water temperature, light and nutrients".

Although it is present all year round, spring and summer are the periods of greatest growth, because this is when there is more sunlight, longer days and temperatures are higher. It is also, unfortunately, when they cause the most inconvenience on the social level for beach visitors. Asian algae tends to live in quite deep water. "It is rare to see it at the surface. It usually appears at a depth of one metre. If you're already seeing it in the intertidal zone [where the sea meets the shoreline between high and low tides], you can be sure that it's in the subtidal [the zone where there is shallow water even at low tide], in the submerged rocks."

"We need all levels of government to get involved because this is a major problem. There is even talk of it being a catastrophe," said Dr Iván Franco, researcher in the Structure and Dynamics of Aquatic Ecosystems group at UCA. The environmental impact is devastating. "It affects biodiversity because it is growing a lot and is eliminating other algae communities. The large deposits of algae that are formed not only kill flora but also fauna such as invertebrates," added Vergara. Moreover, large accumulations of such algae cause a loss of oxygen in the water.

Invasive algae also affects tourism for Cadiz province. A shoreline full of algae gets a bad press from those who visit from abroad. "To have it talked about that the beaches of Cadiz have been invaded by seaweed is very bad news," said Antonio de María Ceballos, president of Horeca (an association and branding for the hospitality sector in Spain), although he cannot say whether in previous years the seaweed's presence has been detrimental to the sector. It does mean bathing is practically impossible and unpleasant, despite the fact that these large deposits of algae "in principle are not toxic for people". "If they keep up with the collection and removal of the algae, then that's a different matter, but if for economic or logistical reasons the days go by and it's not removed, it would be disastrous," said Ceballos.

To cover the cost of cleaning and removing the large quantities of Asian algae along the beaches that can reach almost a metre in height, the provincial government of Cadiz has increased the budget for the aid programme going to the local councils of Tarifa, Barbate, La Línea, Algeciras and Conil by a further 25%. The subsidy totalling 340,000 euros is shared out according to "the estimated cost of cleaning and removing algae deposits on the beaches". Thus, Tarifa will receive 140,000 euros, Barbate 92,000, La Línea 70,000, Algeciras 20,000 and, finally, Conil will receive 18,000 euros.

This is the first time that Conil has been included in the aid programme. The situation in Conil is getting worse and worse. One of the sectors that is suffering the most is the fishing industry. "I have fleets in the tuna fishing area and every now and then they come back laden with algae," said Nicolás Fernández, president of the Federation of Fishermen Guilds of Cadiz. Furthermore, the fact that it is not possible to fish in Barbate means that the fleet has to move to waters where this invasive species is less present. "For our boats from Barbate it is impossible for them to go out fishing and not return loaded with seaweed; therefore, they move to Conil and both fleets occupy, thanks to the efforts of our fellow fishermen, 25% of an entire fishing ground that was previously only used by the local fleet."

Fernández also flags up that fish species have been lost. "There are species that have disappeared: sablefish (aka black cod), jack mackerel, redfish and grouper. "The fleet that covered the Strait, Conil, Barbate, Tarifa and Algeciras landed 800 tonnes of sablefish in 2015, 600 kilos in 2019, and from 2020, zero."

Faced with a problem of this magnitude, the first question that comes to mind is what is the solution. "Invasive species are very complicated. The solution is to adapt: often invasive species, after a period of time and an explosion of growth and development, will level out and adapt to the habitat; but there are times when it invades everything and may be here to stay," explained Iván Franco. Along the same lines, Juan José Vergara argued that "over the years this problem will end up being resolved, but almost in a natural way".

In an attempt to mitigate the impact of this invasive species, researchers are studying what use(s) it can be put to. "They are trying to make compost with it or use it as biofuel." Regarding the possibility of the sea urchin feeding on this organism: there are different views and contradictory research on this option.

"Several research groups say that the sea urchin can eat it up, but another group has asserted that the seaweed is toxic to the sea urchin, causing it harm. Besides, how many sea urchins would you have to have to bring this invasion under control? There aren't enough of them to eat it all. Biological control by consumption is difficult with this algae because it has a certain toxicity," said Vergara.

Prevention and control in ports is vital to avoid future invasions of other species. "What needs to be done to control invasive species is early detection. And that means monitoring and surveillance of those places where an invasive species is most likely to enter. The solution started 15 years ago, because in order to find solutions you need data," concluded Iván Franco.