The density at which an organism occurs in a habitat has previously been considered a factor that may itself enhance or inhibit the rate of survival. This result may arise through direct interactions between the conspecifics or through an intermediary agent such as a predator. A pattern where the survival rate is inversely related to density may also arise in the absence of biotic interactions. Two cases that depend on habitat selection behavior will be discussed. First, high-density aggregates may have disproportionately low representation of viable stock. Second, favorable micro-sites within habitats can be occupied by early recruits without turning off the cue that attracts recruits to the habitat. However, the hypothesized features that affect survival, such as individual differences between recruits and favorable characteristics of the habitat, are not observable. The barnacle, Semibalanus balanoides, provides a useful system for addressing these habitat selection hypotheses, because it is possible to follow individual recruits. We record the time and micro-site that an individual recruits, and we can keep track of it until its death.

Results/Conclusions

We report success from grouping individuals by settlement date to identify different temporal cohorts in the recruit population. Barnacles consistently recruited in higher density in one habitat, but the consequences for their survival to adulthood varied by season. During the winter, barnacles recruiting in higher density had higher mortality. Conversely, spring recruits survived equally in both habitats. At a finer scale, we resolved the time of settlement in different micro-sites within each habitat. Overall survival was well described by the fine scale settlement timing. These patterns of recruitment and survival are useful for distinguishing between alternative hypotheses on the role of habitat selection for barnacle fitness.