Bathymetric patterns of α and β diversity of harpacticoid copepods at the genus level around the Ryukyu Trench, and turnover diversity between trenches around Japan

The diversity of harpacticoid copepods was investigated around the Ryukyu Trench (430–7150 m), which lies below an oligotrophic subtropical ocean. The α diversity, which is based on the number of genera and Shannon diversity decreased with increasing water depth. The community structure of harpacticoids gradually changed as the water depth increased from the bathyal zone to the hadal zone. Turnover (β) diversity values were equally high between the trench slope, trench floor and abyssal plain. We compared the harpacticoid assemblage obtained from the Ryukyu region with the assemblage from a region around the Kuril Trench (Kitahashi et al., 2013). Turnover diversity values between the two regions (δ diversity) were relatively low at shallow depths, but they increased with increasing water depth and reached their maximum between the trench floors and abyssal plains. These findings indicate that the bathymetric patterns of harpacticoid assemblages differ among regions and that these discrepancies reflect differences in environmental conditions, such as primary productivity level.