PARENT SESSION
Symposium 22: Expanding Scales, Expanding Perspectives: New Insights into Marine Ecosystem Dynamics
Organized by: P Raimondi and B Menge
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Oglethorpe Auditorium.

Marine masting: episodic prey recruitment and the synchrony of community dynamics on large spatial scales.

Witman, Jon^*,, Genovese, Salvatore, Bruno, John, Altieri, Andrew,

ABSTRACT- A massive subtidal recruitment of the mussel, Mytilus edulis, across the SW Gulf of Maine (GOM), USA provided an opportunity to test the hypothesis that the episodic increase in food resources had a bottom up effect on mussel consumers. Surveys across a 120 km marine landscape revealed that juvenile mussels covered 33 to 91 % of the bottom (8 to 12 m depth) from October 1995 to June 1996. The cover of mussel prey explained significant variation in the density and biomass of mussel predators (sea stars, rock crabs) at 16 to 17 sites 10, 13 and 23 months after mussel recruitment, consistent with hypothesized bottom up effects. Coupling between bottom up and top down control occurred 12 to 14 months after mussel recruitment when predation by sea stars, crabs and sea urchins eliminated extensive beds of juvenile mussels across the region. The elimination of mussel prey triggered cannibalism in the sea star Asterias vulgaris, which contributed to density-dependent sea star population declines from 1996 to 1997. An assumption of the consumer reproduction and recruitment response, that larvae produced by adult stocks of consumers could be retained in the study region, was supported by investigations of the potential larval dispersal of sea stars and crabs in a simulated 3D flow field of the SW GOM. In this study, massive prey recruitment stimulated coupling between bottom up and top down forces, resulting in broad scale changes in local consumer populations that persisted after the prey recruitment signal was removed, underscoring the importance of episodic events in marine community dynamics. A review of long term data suggests that episodic, large recruitment of prey species is an important feature of benthic marine ecosystems. Like the phenomenon of mast seeding in terrestrial ecosystems, it has the potential to synchronize population and community dynamics across broad spatial scales.

Key words: food webs, top down, large spatial scale, bottom up