Biotic dispersal in eelgrassZostera marina

Dispersal is a critical process in the life history of nearly all plant species and can be facilitated by both abiotic and biotic mechanisms. Despite an abundance of vertebrate fauna utilizing seagrass meadows as a feeding area and thus capable of consuming and excreting seeds, little work has been conducted on biotic seed dispersal mechanisms. The objectives of this study were to (1) determine whether seeds of the seagrassZostera marinacould pass through the digestive systems of resident and transient vertebrates of a seagrass bed and remain viable and (2) determine seed retention times in the guts of each species to estimate dispersal distances ofZ. marinaseeds by vertebrate dispersers. Excretion and germination rates of consumed seeds for 3 fish species (Fundulus heteroclitus,Sphoeroides maculatus,Lagodon rhomboides), 1 turtle species (Malaclemys terrapin) and 1 waterfowl species (Aythya affinis) showedZ. marinaseeds could survive passage through species’ digestive systems and successfully germinate. Excretion rates were generally highest forF. heteroclitus,S. maculatus, andM. terrapin, lowest forA. affinis, and moderate forL. rhomboides. Analyses suggest seeds were significantly affected by species’ digestive tracts. Maximum dispersal distances are estimated to be 200, 60, 1500, and 19 500 m forF. heteroclitus,L. rhomboides,M. terrapin, andA. affinis, respectively. Data here provide strong evidence that biotic dispersal can occur inZ. marina, and biotically transported seeds can be dispersed to isolated areas unlikely to receive seeds via abiotic mechanisms. Biotic dispersal may rival or exceed abiotic mechanisms. Future seagrass dispersal models should incorporate biotic dispersal as a seed transport mechanism.