Coral reefs are increasingly affected by high-temperature stress events and associated bleaching. Monitoring and predicting these events have largely utilized sea surface temperature data, due to the convenience of using large-scale remotely sensed satellite measurements. However, coral bleaching has been observed to vary in severity throughout the water column, and variations in coral thermal stress across depths have not yet been well investigated. In this study, in situ water temperature data from 1999 to 2011 from three depths were used to calculate thermal stress on a coral reef in Bahia Almirante, Bocas del Toro, Panama, which was compared to satellite surface temperature data and thermal stress calculations for the same area and time period from the National Oceanic and Atmospheric Administration Coral Reef Watch Satellite Bleaching Alert system. The results show similar total cumulative annual thermal stress for both the surface and depth-stratified data, but with a striking difference in the distribution of that stress among the depth strata during different high-temperature events, with the greatest thermal stress unusually recorded at the deepest measured depth during the most severe bleaching event in 2005. Temperature records indicate that a strong density-driven temperature inversion may have formed in this location in that year, contributing to the persistence and intensity of bleaching disturbance at depth. These results indicate that depth may not provide a stress refuge from high water temperature events in some situations, and in this case, the water properties at depth appear to have contributed to greater coral bleaching at depth compared to near-surface locations. This case study demonstrates the importance of incorporating depth-stratified temperature monitoring and small-scale oceanographic and hydrologic data for understanding and predicting local reef responses to elevated water temperature events.

Using global physical and biological datasets, we tested oceanographic retention (factoring out effects of seamount depth and age) as one possible mechanism structuring seamount benthic 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 theory. This was then separately compared to decapod and gastropod taxonomic distinctness, our metric for the community's response to oceanographic retention. Taxonomic distinctness is a metric based on phylogenetic relatedness between species. Therefore, between-seamount variability in taxonomic distinctness may reflect the effects of long-term oceanographic retention at the seamount spatial scale. Taxonomic distinctness and retention potential varied between seamounts, but retention 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.