INTERTIDAL RESEARCH
 
My MSc work focused on predator-prey interactions within rocky intertidal communities. The outer Bay of Fundy, Canada, hosts rocky intertidal communities often dominated by beds of blue mussels (Mytilus edulis), which support vertebrate and invertebrate predators at different times of the year. Strong predation by diving ducks in this system opens the possibility of a trophic cascade whereby ducks substantially reduce mussel density, opening space for other species. However, previous work has shown no long-term cascading effect; compensation from invertebrate predators seems to be inherently present within the system. I examined the temporal effects of predation and how this was related to compensatory action by invertebrate predators via exclosure experiments which were initiated at different times, one in spring and the other in fall. Exclosures excluded ducks and allowed variable access to different invertebrate predators within the community. As predicted, ducks had a substantial effect in both cases, reducing mussel density in areas where they could feed. However, the timing of duck exclusion was crucial in determining compensation. When duck exclusion occurred before the fall migration, the full range of mussel sizes remained present within the system and whelks compensated. In contrast, when exclosures were set up after duck foraging had commenced, the remaining mussels were generally larger and green crabs (Carcinus maenas) compensated but whelks did not. This research​ highlights the need for careful consideration of the timing of manipulative studies to ensure that results are not artifacts of seasonal variation in predator activity.