Zooplankton composition and distribution in the Benham Rise as affected by the North Pacific western boundary currents

The Benham Rise is an extinct volcanic ridge rising from depths of 5000m to form a shallow plateau including a seamount with a peak that reaches about 50m below the surface. It is situated in a hydrodynamically active area where major oceanic currents in the Northern Pacific converge and originate. The interaction of the western boundary currents with the Benham Rise can lead to enhanced biological productivity. This area has been found to harbour deep reefs and is also a known fishing area. This study was conducted to help understand this productivity.  Samples for zooplankton were collected during the Benham Rise Cruise last May 2014  Samples were analyzed for composition and biomass. Representative stations were chosen near the Benham bank for the identification of the species occurring in the area.  Biomass samples were further sieved into different size classes (2000, 1400, 1000,640, 200 µm).  Highest biomass was found at the size class of above 2000 µm followed by size class above 200 µm.  Initial analysis showed that jellies dominated the samples sieved with 2000 µm while crustaceans, particularly copepods, dominated the samples sieved through 200 µm mesh. Size-class composition and biomass across stations were also compared.