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Plankton abundance and size structure in the northern North Pacific Ocean in early summer
Author(s) -
ODATE TSUNEO
Publication year - 1994
Publication title -
fisheries oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 80
eISSN - 1365-2419
pISSN - 1054-6006
DOI - 10.1111/j.1365-2419.1994.tb00104.x
Subject(s) - zooplankton , phytoplankton , oceanography , abundance (ecology) , plankton , environmental science , biomass (ecology) , food web , grazing pressure , grazing , nutrient , ecology , biology , trophic level , geology
Phyto‐ and zooplankton abundance and size structure were investigated in the northern North Pacific Ocean (37.0–49.5 o N along 180 o longitude) during June of 1987. The area between 41.5 o N and 47.5 o N was expected to be abundant in phytoplankton since both water column stability and nutrient availability were favourable for phytoplankton growth. Actual phytoplankton abundance was, however, low between 41.5 o N and 45.5 o N. In particular, abundance of net phytoplankton (>10μm) was low although picophytoplankton (<2 μm) was abundant between 41.5 o N and 43.5 o N. The zooplankton community between 41.5 o N and 45.5 o N was characterized by a large amount of net zooplankton and a small amount of microzooplankton. This situation may be best explained by top‐down control; that is, net zooplankton grazing suppressed net phytoplankton and microzooplankton abundance. The diminished microzooplankton promoted the increase of picophytoplankton. Because planktivorous Pacific saury were abundant between 40.0 o N and 41.0 o N, it is further speculated that the low biomass of net zooplankton south of 41.0 o N resulted from feeding by Pacific saury. The reduced grazing pressure of net zooplankton may have enhanced the growth of net phytoplankton and microzooplankton in this region.