The potential for dispersal of microalgal resting cysts by migratory birds

Most microalgal species are geographically widespread, but little is known about how they are dispersed. One potential mechanism for long-distance dispersal is through birds, which may transport cells internally (endozoochory) and deposit them during, or in-between, their migratory stopovers. We hypothesize that dinoflagellates, in particular resting stages, can tolerate bird digestion; that bird temperature, acidity, and retention time negatively affect dinoflagellate viability; and that recovered cysts can germinate after passage through the birds' gut, contributing to species-specific dispersal of the dinoflagellates across scales. Tolerance of two dinoflagellate species (Peridiniopsis borgei, a warm-water species and Apocalathium malmogiense, a cold-water species) to Mallard gut passage was investigated using in vitro experiments simulating the gizzard and caeca conditions. The effect of in vitro digestion and retention time on cell integrity, cell viability, and germination capacity of the dinoflagellate species was examined targeting both their vegetative and resting stages. Resting stages (cysts) of both species were able to survive simulated bird gut passage, even if their survival rate and germination were negatively affected by exposure to acidic condition and bird internal temperature. Cysts of A. malmogiense were more sensitive than P. borgei to treatments and to the presence of digestive enzymes. Vegetative cells did not survive conditions of bird internal temperature and formed pellicle cysts when exposed to gizzard-like acid conditions. We show that dinoflagellate resting cysts serve as dispersal propagules through migratory birds. Assuming a retention time of viable cysts of 2-12 h to duck stomach conditions, cysts could be dispersed 150-800 km and beyond.