Effects of oceanographic retention on decapod and gastropod community diversity on seamounts

Using global physical and biological datasets, we tested oceanographic retention (fac- toring out effects of seamount depth and age) as one possible mechanism structuring seamount ben- thic decapod and gastropod communities. We first determined the relative oceanographic retentive potential (such as from Taylor caps or columns) for individual seamounts based on steady-state the- ory. This was then separately compared to decapod and gastropod taxonomic distinctness, our met- ric for the community's response to oceanographic retention. Taxonomic distinctness is a metric based on phylogenetic relatedness between species. Therefore, between-seamount variability in tax- onomic distinctness may reflect the effects of long-term oceanographic retention at the seamount spatial scale. Taxonomic distinctness and retention potential varied between seamounts, but reten- tion did not explain variation in taxonomic distinctness. Among decapod communities, variation in taxonomic distinctness was partly explained by seamount summit depth. With respect to previously suggested causal relationships between seamount retention and biogeographic patterns (divergent seamount communities, high rates of endemism, and inferred speciation at the scale of the seamount), we concluded that seamount-scaled oceanographic retention is weak compared to other ecological drivers of community diversity on seamounts. Alternative processes (such as those related to depth), or alternative spatial scales (within each seamount or between seamount groups and chains) must be considered to explain divergent patterns among seamounts for these taxa.