| "We were able to determine that when the pesticides came on site, we would see a reduction in the fiddler crab population." | |
| Mike Shirley, Rookery Bay National Estuarine Research Reserve |
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While most people consider mosquitoes an annoyance, the pest's disease-carrying ability makes them a serious enough concern that communities may try to control the insects by spraying pesticides. Scientists at a Florida National Estuarine Research Reserve have shown that nearby pesticide applications impacted the Reserve's crab population.
"Mosquito control is a necessary evil," says Mike Shirley, resource management coordinator at Rookery Bay National Estuarine Research Reserve in Naples. "But you have to balance the needs of reducing the mosquito population with the environmental impact."
Shirley and Charles L. McKenney Jr., a researcher from the U.S. Environmental Protection Agency, discovered the impact mosquito control was having in the Reserve in 1992 while monitoring a newly restored mangrove habitat. "We noticed a peculiar die off of fiddler crabs," Shirley explains. "We knew something had happened. We thought it might be a water quality issue." A little detective work by the two revealed that a mosquito control plane had sprayed pesticides near the Reserve the night before.
The scientists approached the Collier County Mosquito Control District with their observations, and the agency agreed not only to coordinate when pesticides were to be sprayed, but to provide funding to research the problem. The project also received a grant from the National Oceanic and Atmospheric Administration Office of Ocean and Coastal Resource Management Sanctuaries and Reserves Division.
The researchers set up two sites adjacent to each other in the mangrove forest where the impacts on fiddler crabs were much different. The only variance was that one of the sites had a canopy of trees provided by an older mangrove stand. "The pesticides caught on the canopy of leaves so not as much would make it to the ground," Shirley explains. Water quality was eliminated as a possible source of the die off because the water base was the same for both sites.
At both sites, the scientists put out filter paper to catch pesticides on the ground, and the Mote Marine Laboratory analyzed the pesticide concentrations on the paper. "We were able to determine that when the pesticides came on site, we would see a reduction in the fiddler crab population," Shirley says. They were also able to determine the wind speed and wind direction that caused the pesticide to drift onto the Reserve.
What the scientists found was that 30 percent of the time mosquito pesticide was sprayed on the periphery of the Reserve, there would be drift that would affect the fiddler crab population. It was also discovered that the pesticide had a sublethal effect on the biochemistry of the crabs, which could affect crab reproduction in the long term.
Because of the findings, Collier County Mosquito Control has implemented alternative pesticide management practices. According to Shirley, wind speed and direction are now monitored, and during drift conditions, spraying is conducted a mile further away from the Reserve. The agency also has changed the pesticide it uses to one that breaks down more quickly.
Shirley says that Rookery Bay considers mosquito control "one of the top five impacts" to their site. "We're putting this at such a high priority because it's something on which we can have an immediate impact."
For more information on the Rookery Bay National Estuarine Research Reserve mosquito control efforts, contact Mike Shirley at (941) 417-6310, or e-mail him at shirley_m@dep.state.fl.us.
