Large-Scale Sea Turtle Mortality Events in El Salvador Attributed to Paralytic Shellfish Toxin-Producing Algae Blooms

Abstract

In late October and early November 2013 and 2017, hundreds of sea turtles were found dead along the Pacific coastline of El Salvador. The dead turtles were in good body condition and did not have any injuries or other major anomalies. In order to determine the role of paralytic shellfish toxins (PST) in this mass mortality, tissue samples, including blood, flipper, liver, kidney, stomach and intestinal contents, of dead green turtles (Chelonia mydas) and olive ridley turtles (Lepidochelys olivacea) were analyzed for PST using a radioactive receptor binding assay, enzyme-linked immunosorbent assay, and high performance liquid chromatography. Highest values of PST were detected in enteric contents in the 2013 event (7,304.1 µg STX eq kg −1) and in gastric contents during the 2017 event (16,165.0 µg STX eq kg −1). During these events, remotely-sensed chlorophyll-a and fluorescence line height imagery revealed anomalies suggestive of algal blooms off the coast of El Salvador. In the 2017 event, Pyrodinium bahamense was observed in samples of gastrointestinal contents from affected sea turtles. Seawater from the region where dead sea turtles were found was also analyzed, but saxitoxin-producing species were found in low abundance (5400 cell/L in 2013 and 672 cell/L in 2017), which may reflect limited sampling. Although threshold levels of toxicity in sea turtle species are not well-characterized, our evidence suggests that these large events were the result of PST-producing algal blooms and that these blooms are a major cause of sea turtle mortality in this region.

Changing Ocean, Marine Ecosystems, and Dependent Communities

“…Harmful Algal Blooms (HABs) are proliferations of phytoplankton (mostly dinoflagellates, diatoms and cyanobacteria) and macroaglae that have negative effects on marine environments and associated biota. Impacts include water discolouration and foam accumulation, anoxia, contamination of seafood with toxins, disruption of food webs and massive large-scale mortality of marine biota (Hallegraeff, 2010;Quillien et al 2015;Amaya et al 2018;García-Mendoza et al 2018;Álvarez et al 2019). The IPCC 5th Assessment Report (AR5) concluded that harmful algal outbreaks had increased in frequency and intensity, caused partly by warming, nutrient fluctuations in upwelling areas, and coastal eutrophication (medium confidence); however, there was limited evidence and low confidence for future climate change effects on HABs (AR5 Chapters 5, 6) (Pörtner et al 2014;Wong et al 2014b).…”

Saxitoxin Poisoning in Green Turtles (Chelonia mydas) Linked to Scavenging on Mass Mortality of Caribbean Sharpnose Puffer Fish (Canthigaster rostrata-Tetraodontidae)

“…Toxin concentrations were lower in gastric contents than whole fish, which could reflect degradation or absorption. Sea turtle mortality associated with STX-producing dinoflagellate blooms is reported from the Pacific coast of Mexico and Central America, and Papua New Guinea (14)(15)(16)(17). These published accounts reported higher STX toxin concentrations in individual turtle tissues (1.16-4.78 µg STX eq/g) than STXs we detected in green turtles feeding on C. rostrata (approximately 0.04 µg STXs/g).…”

Co-ocurrence of two toxic dinoflagellates in Acapulco Bay, Guerrero, Mexico: an opportunity to quantify their biology and ecology

“…Saxitoxins were recorded in different organs and gastric contents of the turtles up to 1616 µg SXT eq.100 g -1 of tissue, as well as Pyrodinium cells in their digestive tract. However, Pbc was not registered in the water column or it was extremely scarce (20 cells l -1 ) (Amaya et al, 2018).…”