High resolution geomorphological classification of benthic structure on the Western Pacific Seamount

Abstract

The benthic structure of seamounts is critical for understanding the ecological environment and for assessing the influence of resource exploitation. However, the characteristics of the benthic structure of the seamount, especially for guyot, are still far from being clearly understood. For the first time, we carried out detailed hydroacoustic mapping in conjunction with surficial sediment sampling and underwater video recording to investigate the geomorphical and biological characteristics of Pallada Guyot in the Western Pacific Ocean (WPO). We utilized the Benthic Terrain Modeler (BTM) as an initial step to describe the detailed benthic structures and then classify the textural seabed according to backscatter images and sediment samples. We further discussed the relationship between geomorphology and the occurrence of benthic megafauna from video images. The results revealed that 13 classes of benthic structural zones were differentiated, and the dominant zones were flat abyssal plains, where the number and size of megafauna were smaller than those on the flank and flat-topped areas. The second most notable feature is the flat top, where sea cucumbers, starfish, fish, and shrimp have higher biomass and diversity. In the flank region, which is characterized by complex and extensive current-scoured ridges and depressions, sponges and corals are distributed in high-relief bedrocks. We also found that the maximum water depth where cold-water corals develop is 2,250 m. The sponge grounds appear in a marked bathymetric belt (1,800–2,150 m), which is shallower than that on a tropical seamount (2,500–3,000 m) located in the northeastern Atlantic. The findings of this study contribute to understanding the geomorphological drivers and biogeography of WPO seamounts and provide a reference for identifying priority areas for improved marine mineral planning in WPO areas.