Toxin uptake and slowed reflexes by the marine snail Lunella undulata following exposure to paralytic shellfish toxin producing Alexandrium catenella

Comparatively little is known about paralytic shellfish toxin (PST) accumulation by marine grazers, yet recurrent blooms of Alexandrium catenella have caused repeated closures of wild fisheries and require ongoing monitoring. To determine if the commercially harvested periwinkle Lunella undulata is at risk of PST uptake, a laboratory experiment was conducted exposing the herbivorous/detritovorous marine snails to either live or senescent Alexandrium catenella microalgae. After 21 days of exposure, the highest PST concentrations were observed in the viscera of animals in the senescent and live algal treatments (0.55±0.08 and 0.82±0.12 mg STX.2HCl eq./kg, respectively). No quantifiable PST was observed in the foot of animals from either exposure treatment. The PST profile in the viscera closely matched that of the microalgal source, suggesting PST uptake through direct grazing of L. undulata on vegetative A. catenella cells. Grazing activity remained unchanged throughout the exposure period across all treatments. However, periwinkles exposed to A. catenella were significantly slower to retract their foot in response to touch than those animals in the control treatment (first observed on days 7 and 11 in the dead and live algae treatments, respectively). This effect became more pronounced over time and coincided with higher PST concentrations. While righting speed did not differ between animals exposed to live microalgae and the control, those exposed to senescent algae were generally slower to right (observed from day 4 onwards). The implications of these findings for biotoxin management in periwinkles and related marine grazers are discussed.