Bull. Jpn. Soc. Fish. Oceanogr. 75(2), Page 71-81, 2011
  Seasonal changes in abundance, biomass and depth distribution of mesozooplankton community in Kagoshima Bay

Masato Minowa1, Toru Kobari1†, Hiroyasu Akamatsu1, Toshihiro Ichikawa2, Ryuji Fukuda3 and Masataka Higashi4

1 Fisheries Biology and Oceanography Division, Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima, Kagoshima 890-0056, Japan
2 Department of Earth and Environment Science, Faculty of Science, Kagoshima University, 1-21-24 Korimoto, Kagoshima, Kagoshima 890-8580, Japan
3 T/S Nansei-Maru, Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima, Kagoshima 890-0056, Japan
4 T/S Kagoshima-Maru, Faculty of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima, Kagoshima 890-0056, Japan
† kobari@fish.kagoshima-u.ac.jp

Seasonal changes in abundance, biomass and depth distribution of mesozooplankton community were investigated in Kagoshima Bay, to evaluate how mesozooplankton affect sinking flux of particulate organic carbon (POC). Chlorophyll a concentrations were low in March and higher than 1 mg m−3 in August and November when micro-sized phytoplankton was predominated. Mesozooplankton biomass and abundance were uniform throughout the water column in March, while they were concentrated above 50 m in the other months. In March, mesozooplankton larger than 2 mm contributed to their biomass and the most predominant group was of calanoid copepods. In the other months, metazoans smaller than 0.5 mm dominated the community biomass and poecilostomatoid copepods were the most predominant. Based on a box model, mesozooplankton feeding composed only 16 to 33% of primary production in August and November when POC fluxes at 150 m were higher than those in the other months. These results indicate that the high POC fluxes in August and November are resulted from the sinking aggregates of large phytoplankton cells which are not effectively removed by small copepods.

Key words: mesozooplankton, abundance, biomass, depth distribution, vertical carbon flux, Kagoshima Bay