Although we find little support for endemicity among megafauna at Davidson, we do find preliminary evidence that communities are structured differently. Overall we find an assemblage of species that also occurs on adjacent continental margins. A large percentage of these species are also cosmopolitan with ranges extending over much of the Pacific Ocean Basin. Overall, the distribution of range sizes also indicates a fauna broadly distributed as been posited for both deep-sea organisms, and marine faunas in general, but rarely tested in the deep sea. Despite the similarity in composition between the seamount and non-seamount communities, we found preliminary evidence that seamount communities may be structured differently and potentially serve as source of larvae for suboptimal, non-seamount habitats.

The developed database has also allowed us to explore how Davidson Seamount communities vary across the flanks and summit. Both the types and densities of species appear to change as depth increases from the summit to the base of the seamount. Communities at the summits, flanks, and base of Davidson are statistically different. This faunal turnover occurring over a relatively small area suggests Davidson, because of changes in biotic variables that covary with depth, may support a concentration of species.

Biological Characterization of Davidson Seamount: Seamounts have long been characterized as unique and rugged ocean habitats hosting highly diverse and endemic faunas with high biomass. This notion has become the ‘lore’ of seamount biology, even though it has yet to be examined critically. Several alternative hypotheses have been posited for the role of seamounts in both local and global deep-sea biodiversity. The most prominent is the proposition above that seamounts possess highly endemic faunas reflecting hydrographic and topographic features leading to genetic isolation⎯similar to terrestrial islands. Those who challenge this idea propose instead that seamounts serve are oases, centers of high biomass that in turn increase species diversity. These ideas contrast sharply – in one, seamounts serve as a sink for larval recruits originating in adjacent habitats, while in the other, seamounts are a source of larvae for surrounding areas. Alternatively, seamounts may acquire heightened biodiversity through the presence of coral and sponge fields, which promote local species coexistence by offering increased habitat complexity. High biodiversity of seamounts may also reflect rapid habitat turnover associated with substrate type, currents, temperature, oxygen concentration, and other abiotic/biotic parameters encountered across the flanks and summits of the seamount. Currently, the majority of these hypotheses are not adequately or critically evaluated with field data.

Remotely Operated Vehicle (ROV) dives at Davidson Seamount were conducted in 2000, 2006, and 2007 through a collaboration of MBARI, MBNMS, and NOAA. In addition, during some of these dives, quantitative transects were conducted yielding potential diversity per unit area and faunal densities. For example, in June 2007 100m transects were conducted on the north (1754m) summit of Davidson. The beginning of this transects was tagged with a permanent marker (numbered float anchored to the seafloor). Two additional markers were also placed marking Gorgonian corals and may serve as a start point for planned future transects.

Our goal is quantify the faunal densities found along previous transects to serve as a baseline, and making them publicly available through the SIMoN website. In addition, previous transects at untagged areas may also be relocated and serve as a baseline assessment. The goal of this project is to build on previous efforts to compile data from transects into a single cohesive database. In addition, we plan to add vital ecological information about the species. This provides a unique opportunity to evaluate the above hypotheses and further elucidate the importance of Davidson Seamount to the surrounding deep-sea ecosystem. The total dataset will be able to specifically address the links between the near-shore and deep-water areas currently within the sanctuary (DS-2.4) in the context that Davidson serves as a source or sink of larval recruits in the region.