Patch dynamics in beds of the blue musselMytilus edulisL.: Effects of site, patch size, and position within a patch

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Abstract
The blue mussel Mytilus edulis shows spatial aggregation and forms extensive epibenthic beds on both hard and soft substrata. Formation of patches is a dynamic process which may have an adaptive value. Previous experiments have shown that growth of mussels is negatively related to group size. In this study we examine the distribution of shell length, dry weight, and shell weight of mussels occurring in natural beds of two intertidal populations in Danish Fjords. The beds are situated on sand bars formed by tidal currents in the narrow inlets and thus comparable ecologically. Effects of statior-, patch size, and position were tested using three-factorial and nested ANOVA. Effects of recruitment (mussels <20 mm) were tested with nested ANOVA. The results showed large differences in mean size and weight between stations and that mussels sampled along an edge were significantly larger than elsewhere within a patch irrespective of station. Mussels in isolated small patches ( <30 cm diameter) were even larger. No difference in recruitment between stations was evident and recruits were found in greatest numbers in small isolated patches. Patch dynamics on a spatial scale is linked to recruitment, growth and mortality, and our results showed that these factors are density dependent and predictable. Factors influencing the observed patterns are discussed.

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