A turtle mystery in Jamaica Bay, NYC (Diamondback Terrapins) – via Herp Digest

 By DANA RUBINSTEIN 10/30/14 Politico

Something strange is happening to the diamondback terrapin turtles of Jamaica Bay, though there’s some question as to precisely what that strange thing means.

“Nobody has ever seen anything like this before,” said Russell Burke, a Hofstra University ecology professor and one of the foremost experts on Jamaica Bay’s population of diamondback terrapin turtles, the largest concentration in the state. “It’s a puzzle.”

Every summer, female representatives of North America’s only species of brackish- water turtle lumber nervously onto the shores of the Jamaica Bay Wildlife Refuge.

Using their hind legs, they dig a hole in the sand, deposit their “clutches” of eggs, cover them up again, and return to the bay’s polluted waters.

While the population of female turtles nesting in Jamaica Bay has remained constant over the past decade or so, that population’s egg-laying capacity appears to have fallen off dramatically.

“The number of nests that they’re laying has dropped by 50 percent in the last 10 years,” Burke said.

Female terrapins store sperm for as many as seven years and can lay three clutches during their two-month summer nesting season.

But among the more than 1,200 female turtles that Burke has been following for years, those that used to lay three nests are now laying two, and those who use to lay two are now laying one, and those who laid one are now skipping summers entirely.

“It’s like if you had a big population of a thousand humans and normally they would reproduce with some frequency and the frequency has dropped by half,” he said.

At the same time, two other phenomena are complicating the picture: the size of the clutches and the size of the eggs inside those clutches, has each gone up by about 10 percent.

“The drop in total number of clutches by 50 percent just swamps all that,” Burke said. “They’re clearly putting way less energy into reproduction than they used to.”

This means that absent any countervailing change, the population of terrapin turtles in Jamaica Bay, a population that has rebounded dramatically since the days when turtle soup was all the rage, stands to drop over time as the long-lived reptiles die and fewer young ones rise up to replace them.

It also means that the 31-square-mile bay may not be as healthy as thought, despite the government’s substantial efforts to clean and stabilize it. 

“It’s certainly an indicator that something is dramatically wrong with the health of the bay,” said Burke.

Diamondback terrapins eat clams, snails and other invertebrates that live in marshes.

Jamaica Bay is now surrounded by a largely concrete watershed (the Rockaways, J.F.K. Airport, Shore Parkway), but it used to be a natural wonder.

Before European settlement, it had more than 10,000 acres of wetlands. In 1971, it had 4,000.

“At one point we were losing up to 40 acres a year,” said Daniel Mundy, vice president of the Jamaica Bay Ecowatchers.  

Mundy said recent, concerted efforts by the federal, city and state governments to restore the bay have begun to “stem the tide.”

Nevertheless, the city says there are just 1,000 acres of marshland remaining.

There are several working hypotheses as to why: the water quality remains poor and nitrogen rich. The nitrogen promotes algae growth and algae smothers marsh plants. Sea level rise destabilizes marshes.

And the streams that used to carry sediment into the bay have all been paved over.

“All the fresh water coming into the bay is really from sewage treatment plant outfalls,” said Robert Pirani, NY-NJ Harbor and Estuary Program director at the Hudson River Foundation. “There’s not a lot of sediment there.”

So instead of clams and molluscs, the turtles are eating algae.

Burke knows because after he watches the turtles lay eggs, he and his students collect them, soak them in warm water, analyze their excretions and then return them to the bay.

“Sometimes their guts are just filled with algae, that’s what they’re eating,” he said. “At the same time the marshes are degrading really badly and have been for some time. So, my best guess is that our terrapins are eating what they can, because they can’t find what they normally eat. And it’s a really low-protein diet, a really low-quality diet, they probably can’t digest it very well, and that’s translating into reproductive problems.”

And that, in turn, might translate into a disaster for the Jamaica Bay terrapin.

“If you don’t produce eggs to bring young into the population, then there’s only one way for your population to go,” said Burke. “Unless something turns around pretty dramatically, they’re definitely on their way out.”