Things can change quickly when an ecosystem gets set out of balance.
It was less than two weeks ago when the state Department of Environmental Conservation began closing creeks and bays where the shellfish were found to be contaminated with saxitoxin, a nerve toxin produced by the dinoflagelate algae Alexandrium that causes paralytic shellfish poisoning in humans. But since then, diamondback terrapin turtles have been found washed up dead on the shores of Flanders Bay, while dead menhaden, better known locally as bunker, littered the shores of the Peconic River this past weekend.
This is the season for Alexandrium blooms, and this isn’t the first time there’s been such a bloom in our local waters. But the rapid closure of three tributaries of the Peconic Bay and half of Shinnecock Bay, followed by the dead turtles and fish and a warning from the county health department of a “biotoxin” in the water has left the public in a state of shock, grasping at threads of information on exactly what is wrong. And one of the things that might have gone most wrong is the timing of all these events.
Diamondback terrapins awake hungry from hibernation in April, said Karen Testa of Turtle Rescue of the Hamptons, who has helped to collect the dead turtles and send them off to labs at the DEC and Cornell University for testing.
Now, these turtles love shellfish and snails — exactly the food source where saxitoxin is concentrated. Two of the creeks that were closed due to algae blooms — Meetinghouse Creek and Terry Creek — are not far from where the dead turtles were found.
In fact, 40 of the dead turtles were found on Iron Point in Flanders, due south of Meetinghouse Creek, according to the Long Island Coastal Conservation Research Alliance, which also reported that the Alexandrium levels in Meetinghouse Creek were the highest they’d ever recorded.
“They made it through the winter, and then they tried to eat and they died,” said Ms. Testa of the turtles. She said that researchers have ruled out viral and bacterial infections as the cause of the turtles’ demise, and preliminary testing found evidence of saxitoxin in their bodies. She said Cornell University is preparing to study a tissue sample further, a time-consuming process that could take several more weeks.
The DEC has not officially determined a cause of death, but lab tests of the pooled intestine contents of three of the turtles is “suggestive that saxitoxin is present. Circumstantial evidence is consistent with the terrapins being poisoned with saxitoxin, ” said DEC spokeswoman Lori Severino on Tuesday.
“To date, the testing DEC has performed is inconclusive,” she added. “DEC is actively trying to determine the cause of the die off and coordinating with Cornell University’s Wildlife Health Program, which will perform additional tests to try to determine if saxitoxins are the cause of the die-off.”
Alexandrium blooms, like many other algae blooms, tend to follow similar patterns: the algae begin to reproduce at an exponential rate when conditions such as nutrients and temperature are ideal for their growth, but at some point they use up all available nutrients and then they begin to die and decay.
Scientists have found in the past that algae that produce biotoxins often produce the most toxins once they’ve reached the “stationary phase” at the top of the s-curve of exponential growth.
The decay phase uses up the dissolved oxygen in the water, creating what is known by scientists as a “hypoxic condition.”
At this stage in algae blooms, fish begin to suffocate. We’ve seen this before in other local waters — in Mill Pond in Water Mill and Lake Agawam in Southampton, both of which have suffered blue-green algae blooms, with little tidal flushing to bring in fresh oxygenated water.
In Flanders Bay up until now, most bunker that have washed ashore have been driven onto the beaches by bluefish. As recently as 2008, the beaches surrounding the bay are occasionally littered in mid-May with bunker carcasses — a field day for fishermen, who fill coolers with the fish to use as bait. But this year, it seems, something different is at work.
The Peconic Estuary Program, along with the U.S. Geological Survey, measures dissolved oxygen and other water quality parameters at the Route 105 bridge over the mouth of the Peconic River, not far from where the turtles washed up and where the bunker were found.
The graph at right shows dissolved oxygen concentrations between May 12 and May 19, with the concentration dipping below the upper red line — the New York State Chronic Water Quality Standard of just under 5 milligrams per liter — beginning May 13, just before the fish began washing ashore.
According to Peconic Estuary Program researchers, “with the harmful algal bloom occurring in the western estuary, we are experiencing hypoxic conditions. This kind of hypoxia contributes to fish kills, like the one we saw this weekend. Algal blooms and hypoxia are symptoms of excess nutrient loading that have become typical occurrences every spring and summer in the Peconic Estuary.”