Jellyfish may be helping leatherback sea turtles make a comeback (Via Herp Digest)

Jellyfish may be helping leatherback sea turtles make a comeback
Massive blooms of jellyfish are big source of food for endangered turtles

By Ludmilla Lelis, Orlando Sentinel
11:06 p.m. EST, November 25, 2011

It's the annual bane of beachgoers: massive "blooms" of jellyfish. This past summer, when the blooms hit Volusia and Brevard counties, thousands of ocean swimmers felt their sting.

But researchers say the very creatures that are such a nuisance to people could be fueling the comeback of one of Florida's endangered species: the leatherback sea turtle.

The largest of the marine reptiles, leatherbacks used to be rare visitors to Florida shores. But over the past two decades, the number of nests dug at Florida beaches has been increasing. This year's count is 600 nests, one of the highest ever at beaches tracked for long-term trends. Nest counts are the main method of assessing sea-turtle population trends.

This success story of sea-turtle conservation has a possible twist, said Kelly Stewart, a researcher with the National Oceanic and Atmospheric Administration. When jellyfish are abundant, the leatherbacks have a veritable feast, which could help the female turtles reproduce more often.

"Jellyfish, and any gelatinous species, are the preferred food source for leatherback sea turtles," said Stewart, who completed her doctoral thesis at Duke University on these turtle trends. "So, if there are more jellyfish, that may not be good for people, but is good for the leatherbacks."

Jellyfish aren't really fish but gelatinous creatures related to corals. There are more than 1,000 species around the world, and they have a familiar, umbrella-like body and tentacles. Most have the ability to sting their prey, but their main predators, such as leatherback turtles, seem to be immune to the venom.

In recent years, there have been giant blooms around the world, including several cases involving a jellyfish species that is foreign to an area. Cocoa Beach had such a phenomenon over the Memorial Day weekend with an invasion of mauve stingers, a deep ocean jellyfish that is rare in Florida but common in the Mediterranean.

Although there is some evidence that the blooms are increasing in size and frequency, it's difficult to be sure because there aren't a lot of data on the history of blooms, according to a University of Washington study.

Stewart said a connection between more jellyfish and more leatherback nests needs further study but offers a possible explanation for the resurgence of the turtles.

Ranked as an endangered species, leatherbacks are the largest sea turtles and the only ones lacking a hard shell. In the late 1990s, leatherback nest numbers started to climb dramatically, with some Florida beaches seeing annual increases of as much as 16 percent, Stewart said.

Also, the turtle, which historically nested only in South Florida, has been digging nests farther north. Volusia County, for example, rarely saw a leatherback nest 20 years ago but this year had 13, a record. A leatherback turtle that had been tagged with a satellite tracker even dug a nest in North Carolina after digging nests in Florida, Stewart said.

"It is a remarkable increase, and one of the marvels of sea turtles," said Anne Meylan, research administrator with the Florida Fish and Wildlife Conservation Commission. A co-author of Stewart's study, she credits strong efforts to protect nesting beaches and better monitoring.

However, the study found that nests were increasing even in other countries where the protections are weaker. Stewart said she thinks that means the increases relate to what's happening to turtles in the Atlantic as they travel.

That turtles are reaping a benefit from jellyfish feasts would make sense because of the need for females to fatten up to reproduce. Sea turtles typically nest only every few years, building energy reserves during non-nesting seasons. A typical nest contains 100 or so eggs, and turtles often dig two or three nests a season - all of which quickly depletes the reserves, Stewart said.

But if leatherback turtles have plenty of jellyfish to eat, they may be able to fatten up quicker and reproduce more often, she said. "These nesting cycles can be reduced if they don't have a limit on their food supply."