Zooplankton diel vertical migration in the Corsica Channel (north-western Mediterranean Sea) detected by a moored acoustic Doppler current profiler
2019
Abstract. Diel vertical migration (DVM) is a survival strategy adopted by zooplankton
that we investigated in the Corsica Channel using acoustic Doppler current profiler (ADCP) data from April 2014
to November 2016. The principal aim of the study is to characterize migration
patterns and biomass temporal evolution of zooplankton along the water
column. The ADCP measured vertical velocity and echo intensity in the water
column range between about 70 and 390 m (the bottom depth is 443 m). During
the investigated period, zooplanktonic biomass had a well-defined daily and
seasonal cycle, with peaks occurring in late winter to spring (2015 and
2016) when the stratification of the water column is weaker. Zooplanktonic
biomass temporal distribution in the whole water column is well correlated
with biomass of primary producers, estimated with satellite data.
Zooplanktonic blooming and non-blooming periods have been identified and
studied separately. During the non-blooming period zooplanktonic biomass was
most abundant in the upper and the deep layers, while during the blooming
period the upper-layer maximum in zooplanktonic biomass disappeared and the
deep layer with high zooplanktonic biomass became thicker. These two layers
are likely to correspond to two different zooplanktonic communities. The
evolution of zooplanktonic biomass is well correlated with chlorophyll, with
phytoplankton biomass peaks preceding the upper-layer secondary production by
a lag of about 3.5 weeks. Nocturnal DVM appears to be the main
pattern during both periods, but reverse and twilight migration are also
detected. Nocturnal DVM was more evident at mid-water than in the deep and
the upper layers. DVM occurred with different intensities during blooming and
non-blooming periods. One of the main outcomes is that the principal drivers
for DVM are light intensity and stratification, but other factors, like
the moon cycle and primary production, are also taken in consideration.
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