Authors:  Tana Baier Hadsbjerg and Georgia Sarmiento McNeil, Y10

Maintaining the health of the ecosystems in the Mediterranean is vitally important to the preservation of our future, and to do this, Posidonia oceanica, an endemic seagrass to the Mediterranean Sea, is of critical importance. 

Posidonia brings multiple benefits to the environment, and has quite a similar function to the amazon rainforest: they both sequester carbon dioxide and provide oxygen. However, many people don’t know that posidonia meadows are fifteen times more effective. Furthermore, the Posidonia meadows buffers wave intensity, protecting shorelines; and its ecosystems rich in biodiversity, containing around 1,000 different species in them. Despite posidonia being generally quite durable, due to its long leaves and strong roots, its area and expansion has been declining massively because it is harmed by high temperatures and human activities, and to top it all off, the seagrass is now being displaced and eliminated by an algae called Rugulopteryx okamurae.

okamurae is an invasive species in the Mediterranean, native from the Northwest Pacific and was first spotted in France, where it had been introduced along with Japanese oysters. After that, it was spotted in the Strait of Gibraltar in 2015 and was given its invasive status. It now covers 90% of the seafloor at 10 – 20 metres depth in that region, and is spreading rapidly through other areas of the Mediterranean, including Malaga. 

The causes for such a rapid spread throughout the Strait of Gibraltar have been linked to multiple factors. First of all, the algae has cytotoxic properties, which explains why it has no natural enemies and why herbivores do not eat it. Also, it can grow on the surface of other algae, plants and sea animals, resulting in them dying because of a deficiency in sunlight. Moreover, R. okumurae thrives in environments with temperatures above 15ºC, which means that the Mediterranean, with its warm waters, is an ideal habitat for it. Rugulopterix okamurae was first spotted in 2015, the same year when there was an abnormally high water temperature in the area. Therefore, this could associate the spread of the algae with global warming. 

Removing the algae is complicated and has had so far no rates of success. It cannot be displaced by introducing another species, and removing it manually seems unlikely. Therefore, instead of desperately trying to find the solution, we are focusing on how to contain and inhibit R. okamurae from spreading to other areas of the Mediterranean Sea, such as the Balearic Islands.

As scientist at IFISC (Institute for Cross-Disciplinary Physics and Complex Systems) Eva Llabres explains, by taking into account certain factors, such as currents, temperature, sea depth, health of ecosystems, human activity, growing rates of species, and their interaction with each other, experts are able to gather that data and create computer models. These models could provide us with a prediction on R. okamurae’s path and development in the Mediterranean. 

Knowing that R. okamurae can spread through the different water regions and currents of the Mediterranean on its own, it has to be taken into account when making a computer model to predict its path. However, there isn’t much that we humans can do to stop it, since we can’t control the currents. But, on the other hand, when making computer models, one also has to take into account human activity, which is something we can control and that disperses species at much faster rates and further distances. The Mediterranean is a bustling trading area, with boats travelling back and forth all the time. This could result in the algae travelling to a different area, carried by fishing boats, in cargo boats’ ballast waters or in their anchors.

Additionally, it is also important when creating this computer model to take into account the interaction between P. oceanica and R. okamurae. As mentioned before, P. oceanica is generally a durable plant, so when it is healthy, invasive algaes usually have no chance of taking over the environment. However, when the temperature of the water surface goes above 28°C, the seagrass decays massively. These sorts of conditions are perfect for invasive species, because the posidonia is weak, and they can spread and displace it. As the Earth’s temperature increases, the scenario mentioned above takes place more and more often. 

To prevent the spread of R. okamurae, the use of data and modelling can help us predict R. okamurae’s path and know where to act most efficiently, for example, setting up protective measures and extra vigilance in the area. Whilst it is out of our power to change the currents that control the Mediterranean, we can become mindful of boat activities that are carried out and take precautions on where the boat has been, where it’s going and what it’s carrying. Most importantly, it is vital to protect the P. oceanica and ensure that it is strong and healthy, so that invasive species cannot displace it. The most prominent way of doing that is by taking any actions possible to prevent climate change and keep the sea at lower temperatures.

Small actions can also make a large difference in keeping the Posidonia oceanica in good health. You can make one by reducing your carbon footprint, not placing your boat anchor in a posidonia meadow, and not flushing toxic or contaminating substances down the toilet or drain, such as cooked oils, aggressive cleaning products or the contents of your home aquarium (this last thing could result in exotic species ending up in the sea). Furthermore, if you happen to spot an algae similar to R. okamurae, you can inform Observadores Del Mar, a citizen science portal, who will know exactly what action to take next in order to prevent the spread of this invasive species. 

It isn’t just the underwater world that would be benefiting from your small actions, but we as humans would benefit too, since everything and everyone is in some way connected. 

Top left: Posidonia oceanica meadow in the Mediterranean. Photo credit: Martin Colognoli / MedGardens

Top right: Reference: García-Gómez, J. C., Sempere-Valverde, J., González, A. R., Martínez-Chacón, M., Olaya-Ponzone, L., Sánchez-Moyano, E., Ostalé-Valriberas, E., & Megina, C. (2020). From exotic to invasive in record time: The extreme impact of Rugulopteryx okamurae (Dictyotales, Ochrophyta) in the strait of Gibraltar. Science of the Total Environment, 704, 135408. https://doi.org/10.1016/j.scitotenv.2019.135408

Right: Rugulopteryx okamurae (E.Y.Dawson) I.K.Hwang, W.J.Lee & H.S.Kim. Photo credit: M. Altamirano /Algaebase

 

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