PARENT SESSION
Contributed Oral Session 9: Marine Ecology: Disturbance; Dispersal; Recruitment
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal

Spatial structure and demographics of mussel populations in the rocky intertidal.

Petrovic, Filip^*,1, Guichard, Frédéric ¹, ¹ McGill University, Montreal, Quebec, Canada

ABSTRACT- Rocky intertidal ecosystems have been used as model systems for the development of many ecological theories. In many temperate and subarctic coastal habitats, the Blue Mussel, Mytilus edulis is the dominant primary space holder. Mussel colonization is assumed to result from factors affecting recruitment and post-recruitment survival, i.e. competition, predation and habitat configuration. Despite evidence of passive migration and habitat engineering by adult mussels, the contribution to population dynamics of these processes is still unknown. Here we report results from an experiment elucidating the relative importance of 1) adult movement vs. recruitment and 2) of local habitat engineering vs. topographic heterogeneity, for recolonization by mussels in the St. Lawrence Estuary, Quebec. A mussel transplant experiment was conducted by randomly selecting and clearing 50X50 cm patches with similar topographic and biological characteristics in the mid intertidal zone during the spring. To test the hypothesis that local-density dependence (habitat engineering) is an important process for colonization, we transplanted groups of 50 and 175 marked mussels in randomly selected patches and kept the other patches as controls. At the end of the season the abundance and size structure of all species was measured. Results demonstrate that while crevices exhibited higher colonization, mussel transplants, as well as their surrounding cleared substratum, displayed increased rates of colonization compared to controls. Results also allowed quantification of movement patterns of adult mussels and showed that adults are more prevalent than recruits during colonization. While some studies documented occasional movement of mussels following disturbances, our results support the hypothesis that colonization mostly occurs through the movement of adult individuals. These results counter the long-held view that mussel population dynamics are only regulated by recruitment and growth, and suggest that distribution patterns are upheld by the movement of adult mussels, and that habitat heterogeneity mediates the habitat engineering measured as local-density dependent colonization. These results have important consequences for our understanding of regulation and large-scale dynamics of mussel populations.

Key words: Mytilus edulis, population dynamics, habitat engineering, colonization