Many processes occurring underwater have been changing in time. Whether the changes occurred once or are still on-going depends on the factors that influence them. One such factor is temperature. The planet is getting warmer faster than ever because of natural fluctuations, but it is suspected that the anthropogenic impacts are those that affect the warming even more. The multiple consequences, like the presence of alien species, ecosystem shifts, more frequent and longer harmful algal blooms, to name a few, can be observed in the Canary archipelago.
In 2017, there has been an intense bloom of Trichodesmium spp., which is a diazotrophic cyanobacteria. It has the ability to fix atmospheric nitrogen into ammonium that is later assimilated by other marine organisms. After the event, the TV reported that the bloom occurred due to sewage outbursts and that Trichodesmium would potentially invade and poison the sea. All these news were biased because this cyanobacteria actually plays a crucial role in nitrogen fixation globally. As I have mentioned in the other posts regarding the area, the Canary waters are oligotrophic, meaning that the concentration of nutrients is low. Trichodesmium spp. helps mitigate that by taking part in the nutrient recycling cycle. In addition to being diazotrophic, it is also photosynthetic, which means that it takes up CO2 and converts it into O2 and sugar. It therefore contributes to high tropical ecosystem biodiversity.
Among many factors, the increase of temperature above 23℃ has contributed to the blooming. In fact, the warming of the water has been occurring at a faster pace, increasing by approximately 0,30℃ every ten years, and the presence of Trichodesmium has become more frequent. What if this cyanobacteria is not the only one showing off more often? What if there are other species out there? Species that could, on the other hand, be harmful?
In fact, there are. I had the privilege to see one species with my own eyes while scuba diving in the southern waters of El Hierro, the outermost island of the Canary archipelago. On the contrary to Trichodesmium spp. that lives in the water column, I have seen Lyngbya majuscula, which is a nitrogen fixing cyanobacterium that forms benthic mats attached to sediment, rocky bottom, or other substrates such as Cymodocea nodosa seagrass meadows, macroalgae and corals. Between the dives, my supervisor told me that Lyngbya has been overgrowing the benthic communities during the summer periods and that every summer starts to grow sooner and disappears later.
Its presence represents a danger since it shadows the seagrass, macroalgae and corals. By doing so, these communities are unable to get enough light in order to photosynthesise. Moreover, it can produce secondary metabolites that are harmful for humans, too. From tumor promoters, immunosuppressants to cytotoxic compounds, it provokes dermatitis and breathing problems to individuals who come in contact with it. One of the physical factors that appears to promote Lyngbya’s growth is again the increase of temperature. Even though it persists for longer periods, it has not yet caused detrimental impacts such as those observed on the eastern coast of Australia, a place characterised by sensitive ecosystems. But what if things slip out of hands and this cyanobacteria damages the environments of the Canary waters, too? How can we control it?
Monitoring the environment would be one step forward, in order to understand the origin and keep track of its development. Measuring how the biophysical factors change in time and a pre-set space, as well as using a remote operated underwater vehicle (ROV) in order to see whether the blooms extend towards parts of the sea bottom where it was not present before could be two effective monitoring strategies that could help us develop ways of stopping this cyanobacterium from damaging the ecosystems.
There is a lot of work to be done for the future marine biologists and scientists. It is on us to start.
Heimann, K. and Cirés, S., 2015. N2-fixing cyanobacteria: ecology and biotechnological applications. In Handbook of Marine Microalgae (pp. 501-515). Academic Press.
Martín-García, L., Herrera, R., Moro-Abad, L., Sangil, C. and Barquín-Diez, J., 2014. Predicting the potential habitat of the harmful cyanobacteria Lyngbya majuscula in the Canary Islands (Spain). Harmful Algae, 34, pp.76-86.
Haroun, R.J., Gil-Rodríguez, M.C., de Castro, J.D. and Prud’Homme Van Reine, W.F., 2002. A checklist of the marine plants from the Canary Islands (central eastern Atlantic Ocean). Botanica marina, 45(2), pp.139-169.Roelfsema, C.M., Phinn, S.R., Dennison, W.C., Dekker, A.G. and Brando, V.E., 2006. Monitoring toxic cyanobacteria Lyngbya majuscula (Gomont) in Moreton Bay, Australia by integrating satellite image data and field mapping. Harmful Algae, 5(1), pp.45-56.