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Manatee Springs turtles strong despite decline of ecosystem, high nitrates

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By Mark Scohier

Turtle populations at Manatee Springs State Park appear to be strong, according to a scientist contracting with the Florida Department of Environmental protection.
“They’re the easiest of all reptiles to study,” herpetologist Eric Munscher said in a phone interview last week.
Adults, especially females, tend to use the same areas year after year, he explained.  It creates a higher likelihood of recapturing previously tagged animals.
Muscher said most of the turtles are caught by hand, and new turtles that have hard shells are given a small notch on the side of their shell to help identify them in the future.  The softer-shelled turtles get a small number tattooed onto their shells, and some turtles get inserted with a small transponder about the size of a grain of rice.
Munscher, working with a small crew, started sampling turtle populations at Manatee and Fanning springs in June.  In August, the second sampling, he said a four-person crew caught 117 turtles at Manatee Springs in one day.  Manatee Springs has the second highest turtle population of the half dozen springs he’s been studying since 1999.
    About 80 turtles were caught at both springs on Sept. 18 and 19, the most recent sampling.  Munscher said the number of turtles varies depending upon the season.
The turtles at Manatee Springs are mostly adults, which is good, according to Munscher, because turtles take a relatively long time to reach sexual maturity.
“They’re long lived for a reason,” he said.  “They reach sexual maturity at about eight years.  That’s a problem when people are allowed to harvest them for food.”
The Suwannee River cooter, the turtle most prevalent in Manatee and Fanning Springs, was once heavily harvested, he said.
“Turtles cannot sustain harvest.”
In June of 2009, the Florida Fish and Wildlife Conservation Commission passed a rule that prohibits harvesting six turtle species from the wild, one of which is the Suwannee River cooter.
Munscher said the project started in a class he was taking at Pennsylvania State University in the late 1990s.  His professor at the time was interested in the effects of population growth on the ecology of springs.  He said the study began at Wechiwa Springs State Park near Orlando, an area that had seen a population explosion during the late 1990s.
Muscher said turtles are still being sampled at Wekiwa Springs because it takes years to be able to get an accurate picture of what’s going on.
“Studies like this, for a population parameter, you really need to keep doing for a long time.”
He said the study at Manatee and Fanning springs will take several more years worth of data collection in order to be able to notice any trends in turtle populations.
Bryon Maxwell, assistant park manager at Manatee Springs, said he’s glad somebody’s monitoring the turtle population.
“The study is great for us to be able to keep an eye on what’s going on in the environment.”
Manatee and Fanning both have experienced a decline in their ecologies in recent years because of high nitrate levels attributed mostly to agricultural fertilizers and runoff that move relatively quickly through the Suwannee Basin’s porous geology.
High nitrate levels encourage the growth of algae, which changes the transparency of the water and tends to coat aquatic plants to such a degree that they are unable to photosynthesize light.
Plants such as eelgrass no longer dominate the spring run at Manatee Springs.  In its place: thick mats of algae.
Maxwell said the disappearance of eelgrass has a negative impact on other species such as manatees, which feed on the grass while they winter in the 72-degree water each year.
Yet, turtles at Manatee Springs seem to be unaffected by the algae, according to Meschner.  It’s hard to know for sure because nobody, to his knowledge, has ever studied the populations in Manatee and Fanning springs, he said.
“But turtles actually eat it here and hide in it,” he said speaking of the algae blooms.
A similar study by Meschner at DeLeon Springs State Park, also suffering from high nitrate levels, showed a negative impact on turtle populations due to algae blooms run amok.
Meschner said he attributes the large populations of turtles found at Manatee Springs to the high volume of water, about 100 million gallons a day, that gets pushed out of the spring, keeping the algae blooms concentrated mostly around the edges.
He said he hopes to continue his population study as long as possible.