The current climate change projections in the Canary Islands point to a progressive increase in the temperature of the sea water, which foreshadows that the appearance of concentrations of microalgae in the coming years “is to be expected”. The wind is the factor that will determine its presence in the surroundings of the Islands and its arrival on its shores. This is how they expose it from the Biodiversity Service of the Ministry of Ecological Transition, Fight against Climate Change and Territorial Planning.
The accumulations of Trichodesmium erythraeum recorded during the last week in the east and southeast of Tenerife “are the largest detected in a high-resolution image after the 2017 event”, considered “the most intense and lasting episode of all” known in the Canary Islands for the last 15 years. August 2004 and October 2011 were also months with a notable presence of microalgae on the coasts of the Archipelago.
Although Candelaria, and some point of Santa Cruz (Saint Andrew Y añaza), were the most visibly affected places, «Microalgae blooms are not a local phenomenon, although they create social alarm wherever the spots or filaments accumulate», point technicians from the regional government. This cyanobacteria is common in warm subtropical and tropical seas, such as the Canary Islands. «It is not considered harmful by the Intergovernmental Oceanographic Commission of UNESCO (IOC-Unesco, for its acronym in English).
The accumulation at certain points along the coast “is conditioned by the direction of the wind, the currents and the presence of obstacles on the coast, which generate calm zones that can act as traps for the Trichodesmium filaments.” Its formation and dispersion dynamics is very fast, “of the order of hours or days, in the same way as its transport and reach the coast.” Coastal currents are complex and constantly changing, “so real-time prediction of which beach might be affected is difficult. In a matter of hours they can be detected and disappear,” says the Regional Biodiversity Service.
Current recommendation
Last Sunday was when the municipal authorities discouraged bathing on all the beaches of Candelaria, due to the presence of microalgae. A week later, the recommendation is still valid, although the absence of stains due to the concentration of this cyanobacteria does not prevent the use of any bathing area in the Villa Mariana. The case of Santa Cruz was milder, not having to use the recommendation not to bathe in San Andrés (not in The Little Teresitas) nor in Añaza.
Although the exact mechanism or combination of mechanisms that trigger the development of Trichodesmium blooms is not known, “in all cases it has been observed that they coincide with an increase in sea surface temperature (more than 22.5° C) , a drastic decrease in the wind (less than 5 m/s), a marked formation of layers of the water column and intense depositions of Saharan mineral dust (abundant haze), although although this last parameter influences growth, it does not seem be decisive”.
Since 2019, the Ministry has carried out periodic sampling in Tenerife, El Hierro and Gran Canaria; Information is obtained on the punctual presence through citizen collaboration through RedPROMAR, collaborators and the environmental monitoring and control service carried out by the boats for the Fight against Climate Change, in addition to the collaboration of other administrations. When blooms are observed, a sample is taken and the Harmful Algae Marine Observatory analyzes them and reports on the organism that forms it, the intensity of the bloom, its possible toxicity and recommendations.
