Latitudinal variations in the abundance, biomass, taxonomic composition and estimated production of epipelagic mesozooplankton along the 155°E longitude in the western North Pacific during spring

- The north-south changes in the mesozooplankton community in the North Pacific were studied.
- The abundance and biomass were at their lowest at low latitudes and highest at high latitudes.
- The dominant zooplankton taxa varied with abundance, biomass, and region.
- The excess secondary production for food of pelagic fish was greater at high latitudes.

A total of 100 mesozooplankton samples collected with NORPAC nets from a 0 to 150-m depth at latitudinal stations (35-44°N) along 155°E each May from 2002 through 2011 were analyzed. The mesozooplankton abundance at each station varied from 39 to 1106 ind. m−3. The mesozooplankton biomass was consistently higher (80-100 mg DM m−3) in the transition domain (40-42°N) than the biomass in the other domains. An empirical metabolic rate-based carbon budget model indicated that production of mesozooplankton suspension feeders was highest (120-175 mg C m−2 d−1) in the transition domain. A comparison between the production of the mesozooplankton suspension feeders and the food requirement of mesozooplankton carnivores indicated that the latter was well fulfilled by the former in the subarctic and transition domains. However, the food requirement of the mesozooplankton carnivores was near equal to or exceeded the production of mesozooplankton suspension feeders in the subtropical domain. As an annual event, the feeding migration of epipelagic fish to the transition and subarctic domains in summer may be interpreted by their utilization of the excess secondary production (production of mesozooplankton suspension feeders).