||Short-term changes in the mesozooplankton community and copepod gut pigment in the Chukchi Sea in autumn: reflections of a strong wind event
Matsuno, K. Yamaguchi, A. ,
Nishino, S. ,
Inoue, J.Kikuchi, T.
4015 , 2015-07-03
To evaluate the effect of atmospheric turbulence
on a marine ecosystem, high-frequency samplings (two to
four times per day) of a mesozooplankton community and
the gut pigment of dominant copepods were performed at
a fixed station in the Chukchi Sea from 10 to 25 September
2013. During the study period, a strong wind event
(SWE) was observed on 18 September. After the SWE,
the biomass of chlorophyll a (Chl a) increased, especially
for micro-size ( >10 μm) fractions. The zooplankton abundance
ranged from 23 610 to 56 809 ind.m-2 and exhibited
no clear changes as a result of the SWE. In terms
of abundance, calanoid copepods constituted the dominant
taxa (mean: 57 %), followed by barnacle larvae (31 %).
Within the calanoid copepods, small-sized Pseudocalanus
spp. (65 %) and large-sized Calanus glacialis (30 %) dominated.
In the population structure of C. glacialis, copepodid
stage 5 (C5) dominated, and the mean copepodid stage
did not vary with the SWE. The dominance of accumulated
lipids in C5 and C6 females with immature gonads indicated
that they were preparing for seasonal diapause. The
gut pigment of C. glacialis C5 was higher at night and was
correlated with ambient Chl a, and a significant increase
was observed after the SWE (2.6 vs. 4.5 ng pigment ind.-1).
The grazing impact by C. glacialis C5 was estimated to be
4.14 mgCm-2 day-1, which corresponded to 0.5-4.6% of
the biomass of the micro-size phytoplankton. Compared with
the metabolic food requirement, C. glacialis feeding on phytoplankton
accounted for 12.6% of their total food requirement.
These facts suggest that C. glacialis could not maintain
their population by feeding solely on phytoplankton and that
other food sources (i.e., microzooplankton) must be important
in autumn. As observed by the increase in gut pigment,
the temporal phytoplankton bloom, which is enhanced by the
atmospheric turbulence (SWE) in autumn, may have a positive
effect on copepod nutrition.