Shorebird foraging behavior, diet, and abundance vary with harmful algal bloom toxin concentrations in invertebrate prey

We demonstrate how harmful algal bloom (HAB) toxins can change the strength of consumer-prey interactions by altering the foraging behavior of avian predators on rocky and sandy shores. Changes in the foraging behavior and diet of 5 common northern California shorebirds (black oystercatchers, godwits, sanderlings, whimbrels, and willets) correlated with the predicted seasonal variation in paralytic shellfish poisoning toxin (PSPT) concentrations in their 2 major invertebrate prey species, sea mussels Mytilus californianus and sand crabs Emerita analoga, at 2 locations along the California coast. In rocky habitats, when mussel PSPT concentrations exceeded 150 µg saxitoxin (STX) eq · 100 g -1 , oystercatchers increased their consumption of smaller, non-PSPT-accumulating prey (limpets, primarily Lottia spp.), as well as their discard rate of captured mussel tissue. In sandy habitats, when sand crab PSPT concentrations exceeded 150 to 200 µg STX eq · 100 g -1 , shorebird abundance decreased, while their rejection rate of sand crab prey increased. These results confirm the prediction that shorebirds are able to detect and avoid consumption of lethal amounts of PSPT, and that the movement of HAB toxins through the marine food web can alter upper-level trophic interactions.