Over recent years we have all become aware of vast volumes of rotting seaweed strewn all over Western Beach. The smell is pungently putrid and its invasion of the shores is relentless. As of late, trickles of the weed have begun landing on Eastern Beach and Little Bay but on the other side of the bay vast quantities have been washing up relentlessly, drawing attention from major corporations. So, what has changed and why is this algae here? Why has this problem suddenly started and how bad is it likely to get?

Rugulopteryx okamurae is a brown seaweed which originates from the Western Pacific area. I

n 2002 its presence was discovered within the Mediterranean in Thau Lagoon, France. It is postulated that it was brought over through the importation of Japanese oysters, its presence in France drew little concern as the algae was not demonstrating the classic signs of an invasive species; drastically outcompeting the local algae.

It was not until it was discovered in Tangiers, Morocco in 2017, that alarm bells began to ring as this species had seemingly increased its range drastically from the original location in France. Researchers began looking for signs of this species in many coastal regions to be sure it had come from the same source, and they found it, everywhere! Records of the algae were discovered down the Spanish Mediterranean coastline all the way to Algeciras. Investigators also found R.okamurae on the Atlantic coast from Tarifa all the way up to Cadiz and from Tangiers all the way to Ceuta; a Mediterranean invasion had been quietly taking place and we had been caught horribly off guard.


Fishermen began hauling up nets filled with the algae and beaches began to be engulfed with the volumes being washed up. In some cases, the shore has disappeared underneath metre deep quantities of algae. Under the water a similar picture emerged as R.okamurae was engulfing and outcompeting all the other native species. Anywhere you could find a hard substrate you would find the presence of the invader.

Locally we are faring no better. Our western coastline, mainly rocky, has been taken over by the weed and this summer we have already begun to see the algae washing up on Sandy Bay and Eastern Beach. So, what effects will this have on the ecology? After all, isn’t seaweed meant to be in the sea? The First Mediterranean Symposium on the non-indigenous species, which was held in Antalya Turkey, published some worrying findings. Some areas of coastline had been engulfed by up to 90% coverage between a 5-30 metre depth. To put this into context the range is the most important zone for coastal photosynthesis to take place, we are talking about the base of the food web; the potential this has to alter complete ecosystem is very real indeed.


We cannot rely on the herbivores to consume their way out of this issue because published scientific research by Campos De Paula et al has suggested that chemicals within the algae actually suppress hunger of the local herbivores. Anecdotally, we have observed herbivores consuming and stripping the local algaes around R.okamurae which only creates new habitats for the brown weed to colonise. This behaviour is amplified because as R.okamurae colonises more area of coastline it removes the available habitat area for our local algal species and these species are a food source for local herbivores. Instead of eating part of an algae, hungry herbivores are stripping rocks bare of any food available on them.  Consequently, it appears that our local herbivores are actually aiding the conquest of our coastline which could spell disaster for local diversity.

So how serious is this invasion? Each year, Spain removes around 5000 tonnes of algae from its coastline between Cadiz and Tarifa. This comes at a substantial cost for the region and is a very short-term measure as the algae keeps washing up. Further, if, as predicted, the situation continues to worsen, it could have profound consequences on their valuable tourist industry along its southern coastline. Cepsa, Endesa, Acerinox and the Spanish Electric Network are financing a €400,000 research project lead by the University of Seville into how they can control the invasion and its potentially devastating consequences. Perhaps that seems like a small sum to some but the fear is very real and a research project of that magnitude speaks volumes.

Chemicals within the algae actually suppress hunger.

So, what will happen and what can we do about it? My position on the matter is clear; to quote a line from Jurassic Park, Dr Ian Malcom says “Life, uh, finds a way!”. Mother Nature has been through much worse than this, and she typically comes out on top. The pause for concern which should be on our minds as a species is if that solution contains us as a necessary component.

Rocky substrate
Interesting Fact:
The Mediterranean invasion of this algae is presently in full swing with potentially catastrophic consequences.