Habitat variation influences movement rates and population structure of an intertidal fish

Understanding how variation in habitat characteristics influences the demography and behavior of organisms is of primary interest in ecological research. I studied how patterns of distribution, abundance, mortality and movement of the fluffy sculpin, Oligocottus snyderi, are related to variation in habitat characteristics within and between sites. The recruitment levels of O. snyderi are very similar at two different intertidal sites, yet post-recruitment processes modify the original recruitment signal at only one of the two sites. The two sites differ significantly in only one measured aspect of their tidepool habitat-the amount of cover provided by surfgrass or algae. Both recruits and adults of O. snyderi exhibit positive associations with the amount of tidepool cover, particularly the presence of surfgrass. A mark-recapture study determined that these differences in the habitat characteristics between the two sites are associated with differences in post-recruitment movement rates. In fact, the absence of a correlation at one site between O. snyderi recruit and adult abundances, which would typically be considered evidence for significant post-recruitment mortality, appears to be driven by strong within-site post-recruitment movement. Furthermore, although post-recruitment mortality rates do not vary significantly across the two sites, variation in post-recruitment mortality is weakly related to within-site variation in tidepool characteristics at one site. The results of this study suggest that post-settlement intertidal fishes continue to sample their surrounding environment as they mature and will redistribute themselves according to within-site spatial variation in habitat characteristics-a behavioral process that may obscure estimates of post-settlement mortality.