Habitat heterogeneity as a consequence of substratum-orientation and kelp-canopy: Relating interdependent responses to common patterns

Much of our understanding of the relationship between canopy-forming species and benthic organisms is based on work done on horizontal surfaces, yet the orientation of substratum is known to have striking and widespread effects on benthos. An explicit quantitative understanding of the extent to which habitat related patterns on horizontal surfaces are representative of vertical surfaces is currently lacking and is needed before we can sensibly propose models that account for some of the major sources of subtidal heterogeneity. We tested the hypothesis that the influences of kelp forests (i.e. canopy vs no canopy) on benthic organisms living on horizontal surfaces are different from those on vertical surfaces by testing for an interaction between the factors: habitat (i.e. canopy vs no canopy) and orientation (i.e. horizontal vs vertical). We found that for 5 of the 6 benthic taxa studied, differences between habitats that were detected for one orientation were not apparent for the alternate orientation. Our rejection of the null hypothesis and quantitative evidence of orientation and habitat specific differences (i.e. each combination has unique differences) assisted us to recognize the conditions for which we may reliably anticipate the structure of benthic organisms, thereby improving the predictive power of models that account for widespread patterns in subtidal heterogeneity in this system. This opportunity provided us with a quantitative basis from which we propose an integrated understanding of processes and patterns that until now have been restricted to either habitat (i.e. canopy vs no canopy) or orientation (i.e. vertical vs horizontal substratum).