The dominant copepods Senecella siberica and Limnocalanus macrurus in the Ob Estuary: ecology in a high-gradient environment.
Polar Biology
39(9):1527-1538.
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Intensive transformation and sedimentation of
suspended matter from riverine runoff occur in estuarine
frontal zones. The mesozooplankton community plays an
important role in these processes. In the Ob Estuary, the
dominant copepods Limnocalanus macrurus and Sene-
cella siberica form dense local aggregations, but only
scarce data on the ecology of these species in the estuarine
environment are available. We aimed at analyzing the
main aspects of the ecology of the two species including
their grazing impact on phytoplankton. The distribution
(net tows), ingestion rates (gut fluorescence analysis),
respiration and excretion rates (incubation experiments),
diet composition, gonad development and size of the lipid
sacs of these copepods in a high-gradient area of the Ob
Estuary were studied during a cruise of the R/V Professor
Stockman in September 2013. S. siberica predominantly
inhabited the freshwater zone; L. macrurus was more
abundant in the estuarine frontal zone. In L. macrurus,
adult females and males dominated the population, the
herbivorous feeding hardly met the metabolic demands,
the specific lipid content was high, and the gonads were
developed. In S. siberica, the fifth copepodite stage (CV)
dominated. The feeding rate considerably exceeded the
metabolic requirements, and the lipid content was vari-
able. The gonads were undeveloped. The two species
grazed one-fifth of the phytoplankton biomass and more
than 100 % of primary production, with S. siberica
responsible for the main part of the total grazing impact
(up to 90 %). These results are discussed in connection with the hydrophysical parameters and phase of the pop-
ulation’s life cycle. The obtained results contribute to the
knowledge about zooplankton ecology and the transfor-
mation of suspended matter in an estuarine high-gradient
environment.
