Ecology of ocean beaches: The importance of human disturbance and complex biological interactions within a physically rigorous environment

This dissertation highlights the importance of anthropogenic disturbance as well as complex biological interactions for a benthic community within a physically rigorous, soft-sediment system. Sandy beaches are thought to be structured primarily by physical factors and to have infaunal communities that are well adapted to sediment disturbances. In chapter 1, I investigate the effect of beach nourishment on the macroinfauna of the beach and demonstrate that abundances of several taxa and productivity of the benthic community were reduced following the disturbance. I also conduct experiments in specialized wave-tanks to test hypotheses about specific side-effects often associated with beach nourishment projects (e.g., altered sedimentology, elevated turbidity in the nearshore zone) and the mechanisms by which these physical factors affect beach infauna. Results indicate that elevated turbidity and altered sedimentology can impact beach organisms and slow the rate of recovery of the community.; Biological interactions are considered to be insignificant in structuring communities of high-energy sandy beaches. In chapter 2, I examine a case in which predation may play a role in the evolution and maintenance of intraspecific diversity of the coquina clam, Donax variabilis. The coquina clam is highly polymorphic for both shell color and pattern, and results of predation experiments indicate that such variation provides protection against visual predators. Results also provide support for the hypothesis that both visual selection and apostatic selection are acting on the observed polymorphism. In chapter 3, I evaluate the nature of the often-observed association between Donax spp. and an epibiotic hydroid, Lovenella gracilis (Cnidaria). Field and laboratory experiments reveal that the nature of the association is context dependent and ranges from being mutually beneficial to being detrimental to the host. Chapters 2 & 3 serve to highlight the role of predation in sandy beaches and indicate the need for future studies on sandy beaches to consider biotic interactions as well as a broader range of biotic interactions.