After tallying a death count of 90 marine turtle carcasses on the beaches and in the ocean off Guanacaste, biologists, investigators and conservation officials believe that high levels of toxicity caused by coelenterates such as jellyfish may be to blame for the grisly deaths.
As reported by online news daily CRHoy.com, this Medusa Hypothesis comes after necropsy studies revealed medusoid remain in the stomachs of the perished sea turtles.
The sea turtle massacre has been reported across the Pacific coast of Central America from southern Guatemala down to northern Panama.
As previously reported by the Costa Rica Star, the first gruesome discovery wasspotted by fishermen and later by surfers, swimmers and beach combers:
The dead sea turtles were spotted in the vicinity of Murcielago (Bat) Islands , which are part of a small archipelago located in the Santa Rosa National Park of Guanacaste. This archipelago is a scuba divers’ paradise that is routinely visited by dive tour operators based in Playas del Coco.
Early field necropsies indicate that these turtles, which were tagged near the Galapagos Archipelago, have run into nets and fishing hooks. They also present signs of concussions near their skulls. Still, researchers are conducting pathological analyses to rule out toxicity.
The Medusa Hypothesis
As more dead sea turtles were spotted across the border in Nicaragua, early hypotheses about the use of dynamite for fishing as well as the irresponsible use of trammel nets were formulated since the lifeless bodies showed signs of concussions.
Another possible cause was brevetoxicosis, which is caused by highly toxic and harmful algal blooms. The species affected by brevetoxicosis include green and ridley sea turtles; this poisoning causes neurological damage and erratic behavior that leads to drowning.
A couple of weeks ago, the National Coast Guard Service of Costa Rica flew reconnaissance missions over the areas where the dead sea turtles have been found, and a stain on the ocean akin to red tide was spotted from about the pacific northwest all the way north as far as the human eye can see.
Ocean water samples revealed a large concentration of dead jellyfish, the kind that leaves nasty red welts on surfers and swimmers; in turn, a biopsy performed on the stomachs two surviving sea turtles (including one that may swim again) revealed pieces of cnidarian species.
The Medusa Hypothesis implies that a muscle relaxant and paralyzing substance released by the jellyfish affected the sea turtles and rendered them unable to swim, thus causing them to drown en masse.
The species affected are not carnivores; however, they may have accidentally ingested pieces of dead siphonophore such as Portuguese man-of-war. Giant leatherback turtles are known to eat jellyfish if there is nothing else around to snack on, but they are largely unaffected.
Some residents of Guanacaste’s Gold Coast, which includes beach communities such as Playas del Coco, were concerned that poor wastewater treatment and high concentrations of fecal coliforms in the estuaries and beaches could have been to blame for the sea turtle massacre; alas, that does not seem to be the case.
Toxicity caused by fecal coliform poisoning results in dead fish along the beaches and river mouths, but it tends to remain in the surf and along the coast.
Source | news.co.cr