Experts Suspect Diamondback Terrapin Die-Off Is Caused By A Marine Biotoxin

The East End’s diamondback terrapin turtle population is in trouble—and lawn fertilizers are partly to blame.Since late April, at least 100 terrapin turtle carcasses have washed onto beaches from Flanders Bay in Flanders to Sebonac Creek in Shinnecock Hills. While experts initially thought the die-off was caused by ranavirus, an infection to which many amphibians and reptiles are prone, more and more evidence is pointing to a marine biotoxin that is being absorbed by shellfish, the primary food source of terrapin turtles.The biotoxin, called saxitoxin, causes paralytic shellfish poisoning, or PSP, in people and animals when high concentrations of it are consumed. Karen Testa, founder and director of Turtle Rescue of the Hamptons in Jamesport, said that researchers at Cornell University, to whom she sent most of the carcasses for examination, have determined that the terrapins died after becoming paralyzed, one of the symptoms of PSP.Another piece of evidence is the bloom of alexandrium, a species of red algae that produces saxitoxin, which has been spotted in local bodies of water this season. Earlier this month, the State Department of Environmental Conservation issued bans on shellfishing in most of western Shinnecock Bay, as well as in Weesuck Creek in East Quogue, because of the toxin. The ban on shellfishing in Shinnecock Bay was lifted last week.Kevin McAllister, founder and president of Defend H2O, a nonprofit focused on water quality, said the high amounts of saxitoxin in the South Fork’s waters can be traced to excessive nitrogen in sanitary wastewater that feeds into bays, rivers and estuaries, as well as from fertilizers that leech into the ground and wind up in the water. “We’re seeing these chronic algal blooms virtually everywhere—the common denominator is that they all thrive on excessive nitrogen levels and nutrients,“ Mr. McAllister explained this week. “We’re seeing this massive die-off of them right in conjunction with these blooms,” he said of the turtles. “I’m quite certain, as a scientist, that there’s a direct correlation.”Mr. McAllister also noted that hundreds of menhaden, or bunker fish, have been dying off as well, something that is not unusual with climbing temperatures in the summer, but an occurrence that would be premature at this point in the season, as waters are still relatively cool. He said that die-off can most likely be attributed to saxitoxin too.Ms. Testa said the recent terrapin die-off is worrisome because in the Northeast, the animal is already considered endangered in Rhode Island and a species of concern in Massachusetts. And because the number of terrapins in Long Island waters is unknown, there is no way to gauge how detrimental this die-off is.“We know there’s not an abundance, due to fishermen netting them,” she said. “There’s a lot of predators. They really have a lot of problems. Pretty soon, [they’re] all going to be gone,” she said.At Turtle Rescue of the Hamptons’ headquarters on Manor Lane in Jamesport, rooms are filled with large Rubbermaid containers that hold rehabilitated turtles, many of which are terrapins that managed to be rescued from other incidents before the die-off took place this spring. Some will never be able to live in the wild again and will instead spend their lives in those bins, while at least two are slated to be released next week—something that concerns Ms. Testa, as she fears they may meet the same fate other terrapins have.On Sunday afternoon, she recalled each instance when she and other volunteers first encountered the dead turtles washed onshore. “We got one delivered to us that we thought might be alive. We thought maybe there was a slight chance,” she said, but the turtle didn’t make it.“It’s really detrimental to our population here. The females were loaded with eggs,” she continued. “They’ve been around since the dinosaurs. We just need to clean up our act a little bit.”