- In recent days, different tour guides and residents of the Drake community have found up to 12 dead black turtles (Chelonia mydas) on the beaches of the Osa Peninsula.
August 1, 2022, Ojochal, Costa Rica — As a result of the recent turtle strandings, different national and international marine conservation organizations such as Innoceana, CREMA, Alturas Wildlife Sanctuary and other conservation projects such as the Asociación Conservacionista de la Tortuga Marina del Progreso (ACOTPRO) are joining forces to try to find the cause of death of these marine reptiles.
At this very moment, the Innoceana organization is trying to coordinate with the Drake community so that they collect the bodies of the turtles and send them to the Alturas Wildlife Sanctuary Rehabilitation Center to be able to take measurements of the turtles found on the beaches and do autopsies on the bodies. In order to study which stage of development seems to be most affected, and to be able to determine the cause of death through the relevant scientific analysis.
Although the cause of death is yet to be confirmed, one of the most commented hypotheses is that they have been affected by the great wave of red tides that is currently invading the waters of Costa Rica. Red tides are not a new enemy in Costa Rica and the rest of the world, and in fact they may have natural causes, but in recent years their frequency and impact have increased markedly and it no longer seems to be such a natural process.
Red tides are caused by a bloom of microscopic red algae called dinoflagellates and occur primarily because of high levels of nitrates and phosphates reaching the ocean. Generally, these minerals are a type of nutrients that come from agriculture; but, above all, from pesticides and fertilizers. When the rains increase, the flow of the rivers carries these nitrates and phosphates to the sea, which are a breeding ground for algae, promoting their exponential growth and excessive blooming. Climate change must be added to this cocktail of elements, which has affected the temperature of the waters: the warmer currents and thermoclines are the favorable environment for the proliferation of algae.
During the last 7 months, large masses of red tides have been sighted in the waters of the North Pacific and Central Pacific of Costa Rica; and since the last month, huge outcrops of red tides have also been experienced in the South Pacific coasts, especially in the Osa Peninsula and Caño Island. The impact has been so strong that some Costa Rican marine conservation organizations such as Innoceana, UESPRA, CREMA and the Federation of Artisanal Fishermen and Molluscists of the Gulf of Nicoya, have established a Facebook Group called “Marea roja – Costa Rica | Red Tide Watch Report” where the community can send their reports of red tides and animals affected by it, which is allowing a better understanding of the phenomenon.
During these months, numerous animals affected by red tides have been found both on the beaches and under the sea. Red tides massively affect many types of invertebrates, for example corals, since an increase in bleaching has been observed in them due to lack of light, and there have also been massive arrivals of dead sea urchins on the beaches. . Many of these invertebrates are filter feeders such as sponges and various molluscs, and these are usually the first to be contaminated by the dinoflagellates that form red tides. After the invertebrates and filter animals, the next to be affected are the animals that eat them, such as fish, so it was not surprising that after so many weeks of red tides being affected, many species of dead fish began to be found, generally juvenile reef fish as well as commercial species. These massive and prolonged outcrops now seem to be affecting larger animals and higher up the food chain, so much so that even dead sharks have already been found. The case has already become totally alarming with these latest massive encounters of dead sea turtles, not only in the South Pacific, as some dead turtles have also been reported in the Guanacaste sector.
The hypothesis that the cause of death of these sea turtles is due to red tides is reinforced by a similar event that occurred in 2001, where there was another massive sea turtle mortality event found in Punta Banco and Pavones, in the South Pacific of Costa Rica, also after a prolonged affectation of red tides in the coast. The case was studied by the PRETOMA organization in collaboration with CIMAR scientists and, although the samples of the contents of the turtles’ stomachs were quite deficient, remains of gelatinous organisms known as salps could be found. Salps are filter-feeding organisms, so they could have been contaminated with the dinoflagellates that make up red tides, supporting the theory that the turtles had died from their diet. This is why it is so important to be able to recover the bodies of the turtles and thus be able to study them in depth, especially the contents of their stomachs.
Whether or not they are the cause of the death of these turtles, it is a certainty that red tides are greatly affecting marine life. Little can be done right now to stop the current wave of red tide present in the waters of Costa Rica, but measures can be taken to prevent it in the future. Without adequate legislation that prohibits certain agrochemicals and a clear social awareness that promotes more sustainable practices, this trend in the ocean will only increase.