Published on Thursday, August 20, 2026
By the A.M. Costa Rica staff

The deaths of thousands of purple swimming crabs found along beaches in Guanacaste Province could be linked to warming sea temperatures, according to experts from Fundación MarViva, a regional nonprofit organization.

The organization, which works to protect marine and coastal resources in the Eastern Tropical Pacific, received reports of large numbers of purple swimming crabs (Euphylax dovii), also known as pelagic swimming crabs, washing up dead along several beaches in Guanacaste, including Conchal, Brasilito, Pelencho, Flamingo, Potrero and Penca, among others.

The purple swimming crab is a tropical species found in the Eastern Pacific Ocean. It is recognizable by its reddish-purple shell, long eyestalks and paddle-like rear legs. Its shell typically grows to between 4 and 6 inches long, and the crab spends much of its life swimming in open water.

The species inhabits tropical waters of the Eastern Pacific, ranging from parts of Latin America to occasional sightings in Southern California in the United States.

A sudden increase in sea temperatures or a lack of oxygen in the water could explain the large number of dead crabs, according to MarViva.

However, experts are continuing to analyze the situation to determine the confirmed cause of death of the large numbers of crabs.

MarViva experts recommend that people do not touch or consume crabs found dead on beaches.

People who find additional dead crabs along Costa Rica’s beaches can report the sightings to the foundation by calling MarViva line (506) 4052-2500 or emailing info@marviva.net.

In June, Costa Rica’s National Emergency Commission, known as the CNE, issued a Green Alert for portions of the country’s Pacific region because of an expected decrease in rainfall during the upcoming rainy season.

According to experts, weather conditions for the rest of the year are being affected by the El Niño-Southern Oscillation, or ENSO, a global climate pattern driven by changes in winds and sea surface temperatures in the tropical Pacific Ocean.

The phenomenon is forecast to reduce rainfall by 25% to 50% in some areas. Also, during the warm phase of ENSO, the usual easterly trade winds weaken or reverse. This change stops pushing warm surface water to the western Pacific, allowing a massive pool of warm water to flow eastward toward South America and raise sea surface temperatures.

Fundación MarViva is a regional nonprofit organization founded in 2002 that works to promote sustainable fishing, responsible seafood consumption and marine spatial planning.

CNE works in partnership with communities and emergency responders to strengthen the nation’s preparedness, response, and recovery from natural hazards.

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What actions should Costa Rica take to protect marine species from mass deaths linked to warming sea temperatures? We would like to know your thoughts on this story. Send your comments to news@amcostarica.com