Research Technical Report

Observations and Comparisons of California Seamount Communities

Lundsten, L. (March 2006)

Poster presentation at the Seamount Biogeosciences Network Workshop, La Jolla, CA

INTRODUCTION

Seamounts provide hard substratum, complex habitat, and other conditions which favor faunal assemblages that differ from those found on flat, sediment-covered benthos more typical of the deepsea (Gage and Tyler 1991). Due to these physical characteristics, biological communities found on seamounts may be very diverse, have high abundance, and contain many endemic organisms (Richer de Forges 2000) including unique corals, sponges, and other sessile invertebrates. Enhanced productivity in the water column surrounding some seamounts appears to be associated with the formation of Taylor columns (Rogers 1991) and increased concentrations of zooplankton prey for seamount organisms has been attributed to entrapment of migrating zooplankters (Rogers 1991).

Seamount communities in many regions of the world have suffered at the expense of deep-water fisheries such as those found near Tasmania, where trawling for orange roughy has decimated fragile seamount ecosystems (Koslow, et al. 2001). In this investigation we used video recordings from remotely operated vehicle (ROV) dives to look for patterns of diversity. These ROV dives were conducted for geological studies, yet they provide valuable information about the biological composition of these deep-sea habitats.

The seamounts surveyed in this study, Davidson, Guide, Pioneer, and Rodriguez, all have similar intraplate volcanic origins and each is located atop older oceanic crust which formed 19-20 million years before present (MYBP). These four seamounts have a similar northeast-to-southwest orientation, indicating that they may have formed astride an abandoned mid-ocean ridge system (Davis et al. in press). Though formed under similar conditions, the topography, size, and depth of the seamounts examined here vary (Fig. 1, Table 1). Rodriguez Seamount is unique among this group in that it was subaerially exposed approximately 10 MYBP and is flattopped (Guyot) with rugged flanks and extensive flat regions encrusted with pavements and a thin sediment veneer.