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TWS2022: Pesticides may inhibit blue crab survival
A common pesticide could change physiology and behavior of blue crabs when waterways carry it down to coastal estuaries, which can have larger effects on the ecosystem.
Fipronil is used to treat houses for termites, or to kill ticks on people’s dogs or cats—it’s found in common products pet owners use like Frontline or Termidor. The chemical was also used a lot to kill rice water weevils (Lissorhoptrus oryzophilus), a pest that can cause huge damage to the crops. In all cases, the pesticide can eventually wash into rivers, sometimes through the drains of bathtubs, where people treat their dogs for ticks. Eventually, the fipronil will travel downstream to estuaries where Atlantic blue crabs (Callinectes sapidus) and other creatures live.
Blue crabs serve a critical environmental role in estuaries as they prey on snails that would otherwise eat away at marsh plants.
“Nobody thinks of them about being a keystone species, but they are,” said TWS member Annabeth Rawls.
They also play an important economic role. In Louisiana alone, Rawls said they contribute between $100 million and $300 million to the economy and between 2,000 and 3,000 jobs. “It can really impact us more than we think it can,” Rawls said.
In research presented at The Wildlife Society’s 2022 Annual Conference in Spokane, Rawls, who was finishing her undergraduate degree at Louisiana Tech University at the time, and her colleagues tested the effects that fipronil might have on blue crabs. In a lab, they exposed blue crabs to different levels of fipronil, then ran a number of tests to determine effects the chemical had on the crustaceans.
These tests included timing how long it took for crabs that researchers flipped upside down to turn back over; how long it took for them to settle once researchers initially put them into a water tank; how long it took them to settle down after researchers disturbed them by moving them across a tank; and how well they attacked and consumed snails.
The researchers observed a number of “disturbing things,” Rawls said, especially in the crabs that were exposed to five micrograms of fipronil—the highest treatment in the experiment. One crab had trouble settling in the tank and kept flipping erratically, while another was twitching and spasming. Yet another grabbed onto the rod the researchers used to disturb the crabs and couldn’t seem to let go with its claw. The crabs affected by this highest exposure also didn’t recover their normal behavior after a period.
It’s unclear how high the fipronil concentration is in parts of the Mississippi Delta in Louisiana, since the U.S. Environmental Protection Agency hasn’t tested it. But if the content is as high as five micrograms, Rawls said that the chemical will likely affect crabs’ ability to feed and survive in the estuary.
“Even though fipronil in these higher concentrations can really affect crab physiology and behavior, [the lack of crabs] can also really disrupt trophic cascades,” Rawls said.
She says that the EPA should probably conduct more testing on levels of these pesticides that can affect marine life found in estuaries, even in low concentrations.
On the positive side, low levels of fipronil didn’t affect the crabs much in the experiment. “The lower concentrations exhibited behavior similar to the controls,” Rawls said.