Florida red tide algae toxins can stress and even kill sublegal stone crabs—young adults whose claws are growing toward legal harvest size—according to newly published, preliminary research indicating a strong need for continued studies. Mote Marine Laboratory led the project in collaboration with the Florida Fish and Wildlife Conservation Commission’s Fish and Wildlife Research Institute (FWRI).

Study partners exposed 12 sublegal stone crabs to high concentrations of toxic Florida red tide algae, Karenia brevis, 12 to a less-toxic variety of K. brevis, and 12 to seawater only. Then they used the “reflex action mortality predictor” (RAMP) tool to examine stone crabs’ reflexes—such as retracting a certain body part when it’s touched, somewhat similar to humans’ knee jerk reflex. RAMP gives crabs a number score for reflex impairment, indicating decreased chances of survival.

Over nine days, crabs in toxic red tide conditions showed a 52-percent decrease in reflex scores and a 67-percent decrease in feeding, and they were four times likelier to die than crabs in seawater alone. Crabs in lower-toxin red tide conditions showed less stress and mortality, and crabs in seawater alone showed the least.

The study’s first author, Mote Postdoctoral Research Fellow Dr. Phil Gravinese, said: “This small-scale study is just a first step, but it suggests that these sublegal crabs may have a relatively short window of tolerance for high levels of red tide, and we need to investigate this further.”

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