Mechanisms of infaunal polychaete dispersal and colonization in an intertidal sandflat

Changes in benthic infaunal population densities following disturbance may be influenced by colonization mechanisms. Accordingly, this study experimentally examined the relative importance of four colonization mechanisms for seven numerically dominant polychaete species in an intertidal estuarine sandflat in Connecticut, USA. The colonization mechanism an organism used depended upon species characteristics including larval developmental mode and depth distribution within the sediment. A spionid polychaete with planktonic larval development, Polydora cornuta, colonized experimental disturbance treatments primarily by larval settlement. A surface-dwelling syllid polychaete with nonplanktonic development, Streptosyllis arenae, colonized mainly by bedload transport. Two syllid polychaetes developmentally and morphologically similar to S. arenae, yet deeper dwelling, colonized by different mechanisms than S. arenae. Parapionosyllis longicirrata colonized primarily by burrowing and Brania wellfleetensis colonized by both burrowing and bedload transport. Two other species with nonplanktonic development, Pygospio elegans, and Nereis acuminata, colonized by bedload transport and by burrowing. The more vagile Nereis also colonized by post-larval swimming. Members of the well-known opportunistic sibling species, Capitella, colonized by larval settlement, burrowing and by bedload transport. Although all species were dispersed during sediment transport events at the study site, this transport mechanism appeared to control colonization rate for only the small surface-dwelling species, S. arenae. Colonization mechanisms influenced temporal changes in colonization rates for these species. Colonization rate for P. cornuta was highest during the period of peak larval production. Colonization rate for S. arenae was positively correlated with sediment transport rate. Seasonal changes in colonization mechanisms were also observed. Burrowing and bedload transport were relatively more important colonization mechanisms in autumn when rates of larval settlement and post-larval swimming were low. This study demonstrated that temporal changes in colonization rates for some species could be understood if the primary colonization mechanism was determined