Patchiness in American lobster benthic recruitment at a hierarchy of spatial scales

The overarching goal of ecology is to uncover natural patterns and the processes that underlie them. Importantly, both patterns and processes are dependent on scale. In this study, we assessed spatial patterns in benthic recruitment (density of young-of-year within a few months post-settlement) of American lobster in the Canadian Gulf of Maine by deploying, over 3 consecutive years, between 413-505 cobble-filled collectors on structurally complex cobble bottom in a spatially nested design: regions (127 and 674 km(2)), areas within regions (0.4-4 km(2)), sites within areas (0.003-0.23 km(2)), and sub-sites within sites (0.00004-0.06 km(2)). We quantified spatial patterns of benthic recruitment using a repeated-measures nested ANOVA, variance component analysis and a randomization approach developed for this study. These analyses indicated that the area scale (0.4-4 km(2)) was most important to patchiness in benthic recruitment, with a significant but smaller amount of variation in recruitment at the region scale (127 and 674 km(2)), and virtually no significant variation at the smaller spatial scales. Despite interannual variability in benthic recruitment, these spatial patterns and scales of patchiness were largely consistent across years. Of the 11 study areas surveyed, 3 were identified as recruitment hotspots and 4 as recruitment coldspots, based on density frequency distributions. The location of these different recruitment hotspots and coldspots suggests that patchiness at the area scale may be related to the effect of local currents and topographical features on larval retention. The lack of significant patchiness at the smallest scale of the collector is at first surprising, given previous work on substrate selection by competent post-larvae, but likely arose because our sampling tool offered a standard and high-quality substrate, indirectly confirming the importance of substrate to small-scale patterns of benthic recruitment.