The presence of large stains in the inland waters of El Charco de San Ginés this week has led the Arrecife City Council to request a scientific report to clarify their origin. The council has reported in a statement that these are cyanobacteria of marine origin, which proliferate at certain times of the year.
The Doctor of Marine Sciences from the University of Las Palmas de Gran Canaria, Emilio Soler Onís, a member of the EOMAR research team at the ECOAQUA Institute of the University of Las Palmas de Gran Canaria, has sent this report to the Department of Beaches and Environment of the Arrecife City Council, at the request of the mayor, Yonathan de León. Soler is also accredited by the IOC-UNESCO (Intergovernmental Oceanographic Comission- UNESCO) as an expert in the identification of potentially harmful algae.
"In addition to the climatic effects and marine dynamics of El Charco, there are other factors that also facilitate the appearance of these stains, such as garbage and repair products from anchored boats, garbage dragged by the wind, coastal works have changed the current regime and water renewal inside El Charco, as well as excessive decantation and sedimentation of silts and clays," the report highlighted.
The City Council has indicated that, despite the initial impression of waste or dirt, Mayor Yonathan de León and the Councilor for Beaches and Environment, Davinia Déniz, requested information from the technicians of the Environment Area of the Arrecife City Council on the possible origins of these stains in this area of El Charco de San Ginés.
The council has reported that “Trichodesmium erythraeum is a diazotrophic cyanobacterium capable of fixing atmospheric nitrogen. Common in the oceanic waters of the Canary Islands and with a prominent role in the biogeochemical cycles of the oceans due to the nutrients they release during and at the end of their proliferations, and which can form large stains in coastal areas protected from the prevailing winds and waves. The ability to fix atmospheric nitrogen, together with the ability to reach high growth rates under these temperature conditions, represents a competitive advantage over other photosynthetic organisms.
Specifically, the phenomenon of "massive growth and accumulation" of cyanobacteria is "recurrent" in El Charco de San Ginés and, according to the aforementioned report, has been observed since June 2022. Thus, depending on climatic conditions, such as temperature and weather, as well as the tidal regime, this natural phenomenon can be accentuated and cause large persistent floating stains. They are a consequence of the combined effects of climatology that vary and change rapidly in the short term and human activity that has irreversible effects, if no action is taken in this regard, in the medium and long term.
Colloquially, cyanobacteria are included within the group of microalgae, although they are not, so it is not uncommon to find them referred to in the press and in non-specialized media as "microalgae."
The Doctor of Marine Sciences has indicated that, regarding the relationship between the massive growths of this cyanobacterium with discharges of sewage or urban wastewater, "there are no studies with a proven relationship where urban discharges can generate massive blooms of Trichodesmium like those found in the Canary Islands, nor that the N2 fixation rates increase significantly enough to generate these Blooms."
Therefore, he has assured that "there is no evidence of the effect of wastewater discharges on the formation of blooms or their reactivation." In fact, the reactivation of Trichodesmium blooms "usually always coincides with episodes of increased temperature, decreased wind and the entry of aerosols. On the other hand, these coastal blooms have occurred both in areas affected by discharges and in areas where there is no presence of discharges, such as in the Mar de Las Calmas in El Hierro or in La Gomera."
This expert has highlighted that in social networks and in part of the media of the Islands "the argument of urban discharges has been used to justify a possible relationship with T. erythraeum blooms, creating social alarm and misinformation." Thus, he has indicated that it is "something that is false given that discharges do not increase the rate of N2 fixation in Trichodesmium and therefore do not induce its growth or behavior."
In this line, he has indicated that T. erythraeum is "diazotrophic, that is, it has the ability to fix atmospheric nitrogen and does not depend on sources of nitrogenous compounds such as nitrites, nitrates or ammonium for its growth, that is, it is an organism with a metabolism independent of anthropogenic nitrogen sources."
They are not microalgae
Emilio Soler has highlighted that "Trichodesmium erythraeum is not included in the list of toxic microalgae and cyanobacteria species of the IOC-UNESCO, although in humans it can cause, in exceptional cases, irritation of the mucous membranes upon prolonged exposure, that is, they can have a harmful, but not toxic, effect. There are no registered cases of direct toxicity on people. In case of presence of Blooms, it is recommended not to bathe near Trichodesmium stains, use common sense."
As a result of these data, the Councilor for Beaches and Environment, Davinia Déniz, advocates for citizens to have direct information on this origin, and stop linking the appearance of these stains with discharges.
About Emilio Soler
Emilio Soler has 30 years of experience in the field of Marine Botany and Phycology and 58 publications on deep-sea red algae, cyanobacteria, diatoms, dinoflagellates, HABs and Paleoclimate. He is currently part of the EOMAR research group at the ECOAQUA Institute of the University of Las Palmas de Gran Canaria and develops his scientific work as a research doctor at the Canary Observatory of Harmful Algae of the Canaria Foundation Science and Technology Park of the ULPGC.
He has also participated, as a speaker, in a conference given in the city of Arrecife, in the Municipal Archive, on this topic. These conferences have been organized by the Biosphere Reserve, and with the support of the Arrecife City Council.
