• Different marine conservation organizations warn about the worrying situation and classify it as a national emergency.
  • Dozens of marine species have been found dead in the country’s seas.
  • A virtual group has been created to allow the general public to report cases of red tides

July 22, 2022, Ojochal, Costa Rica — Despite the imminent danger of entering the ocean when there is a red tide, marine biologist Laura Vanopdenbosch went underwater to better understand the situation. After observing several consecutive days of red tide in early July, more research was needed.

Photographs by Yulian Cordero

I didn’t even have 20 centimeters of visibility. It was really terrifying because at one point I lost track of where the surface was and where the seabed was. Either way, I had to inspect the situation since there were dozens of dead species, floating at different depths,” says Vanopdenbosch, who is also the project director of Marine Education and Conservation Center (MCEC). The situation occurred within the framework of one of the marine conservation expeditions that the NGO offers in the South Pacific region. The expedition members —in this case from Argentina, Mexico, the Netherlands and the United States— who were already on the seventh day of their experience, were amazed to see the unfortunate scene of destruction of marine fauna and flora. Even the characteristic decomposing smell of red tide was such that it was impossible to breathe naturally.

Photographs by Yulian Cordero

Red tides are mainly due to high levels of nitrates and phosphates reaching the ocean. Generally, these minerals are a type of nutrients that come from agriculture, pesticides and fertilizers. When rain increases, the river flow carries these nitrates and phosphates to the sea. Algae love these nutrients, causing their exponential growth and excessive blooming. Climate change must be added to this cocktail of elements. The warmer currents and thermoclines are the favorable environment for the proliferation of algae.

Photography by Yulian Cordero

Red tides are therefore a proliferation of microscopic red algae. A big problem with the phenomenon is that light cannot penetrate the dense water columns, which means that corals do not receive enough light for photosynthesis. The result is their whitening and death. The worst aggravation of red tide occurs when the algae die and decompose. Bacteria—which need a lot of oxygen for the decomposition process—take care of the algae, but at a high price, depleting an area of ​​oxygen, which can result in a dead zone. Without properly oxygenated water, marine animals cannot survive: fish, moray eels, sharks, and other creatures begin to die.

Photographs by Laura Vanopdenbosch 

Even though red tides have been around for years and may have natural causes, they are now occurring with worrying frequency. In Costa Rica, the use of pesticides, fertilizers and heavy chemicals is having very negative consequences. Other practices that increase the presence of this phenomenon are constructions with unsustainable methods that provoke sediment and fluvial erosion.

What we’ve seen at Caño Island is alarming. In just this month of July, we have seen hundreds of dead fish, large and small alike, in places that are normally throbbing with life,” adds Vanopdenbosch. During the expedition, huge parrot fish (an indicator species) were found floating on the ocean surface and dead juveniles of moray eels – which are already difficult to spot –, as well as dead snapper and tuna on the seabed. Most of the coral colony (which is normally bright and healthy) has been completely bleached. The participants ended the day in tears as they saw with desolation the state of an ecosystem that is normally vibrant and full of life.

Photography by Yulian Cordero

This problem is a great warning sign. Not only are red tides occurring in Caño Island and the South Pacific region, but also in other parts of Costa Rica. For their part, the inhabitants of the northern zone have also expressed their consternation. Edgar Castillo, director of UESPRA and coordinator of the Hogar Tierra Program in Guanacaste, comments that recently “a sperm whale arrived on the coast, precisely at the Caletas Arío National Wildlife Refuge. It was detected that it arrived due to a type of pathology, surely derived from the red tide in pelagic waters.” For his part, Alan Barrios, president of the Federacíon de Pescadores Artesanales y Molusqueros del Golfo de Nicoya, comments that the islands adjacent to the peninsula are affected by fluctuating red tides.

For this reason, the organizations of the Sociedad de Conservación Marina de Costa Rica (including Innoceana, UESPRA, CREMA and the Federacíon de Pescadores Artesanales y Molusqueros del Golfo de Nicoya) have set up a Facebook group called “Marea roja – Costa Rica | Red Tide Watch Report” where the community can submit their reports. This will allow a better understanding of the phenomenon. Any platform user can subscribe to the group to stay up to date and/or upload reports.

Likewise, organizations are carrying out extensive water quality studies to present statistics that show what is mainly causing these situations. Preliminary studies seem to show that the excessive use of pesticides in the country is not only poisoning consumers, but also the seas. 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.