Latitudinal variations of zooplankton community structure and productivity in the Barents sea (summer 2013)

The Barents Sea is regarded as one of the world’s most unique regions with its high summer productivity. However, there were a few studies dealing with estimation of daily secondary production in the Barents Sea. The aim of the present study was to conduct an investigation of the pelagic mesozooplankton assemblage in the Barents Sea, to calculate daily production levels of mesozooplankton and to analyze the relationship between the community structure and environmental drivers.Structure of zooplankton communities was investigated within the main water masses of the Barents Sea in the summer 2013 (June–July). Calanus finmarchicus presented as copepodites IV–V dominated in terms of the total zooplankton abundance and biomass in Murmansk Coastal Water and Atlantic Water. Spring phase of zooplankton succession cycle was found in Arctic Water where Copepoda nauplii were the most abundant and Calanus glacialis dominated by zooplankton biomass. Zooplankton of the Barents Sea Water had features of spring and summer phases of zooplankton succession cycle. Spatial variations in the zooplankton distribution were associated with hydrological conditions and phytoplankton density. Maximum of the mean zooplankton biomass was registered in Atlantic Water (30,7 mg dry mass/m3) while the minimum was found in Barents Sea Water (5,4 mg dry mass/m3). Calculated daily production of zooplankton ranged from 0,01 to 1,57 mg dry mass/m3per day. Total zooplankton stock for the study area of 281 000 km2was estimated to be > 740 000 t of dry mass. The obtained values of zooplankton biomass and stock were considerably lower than in previous years, which are probably connected with higher predator pressure — grazing of zooplankton by capelin and other predators as well as with possible climatic influence.

Effects of golden perch (Macquaria ambigua (Richardson)) larvae, fry and fingerlings on zooplankton communities in larval-rearing ponds: An enclosure study

In the absence of fish, the plankton community in enclosures in a larval-rearing pond showed a marked successional pattern from rotifers and Moina to copepod and then Daphnia-calanoid dominance. The impact of growing larvae and fry, with densities of 40-118 m-2 at harvest, on zooplankton was conspicuous only after Day 22 when Daphnia became rare and calanoid numbers were suppressed. Predation by fry caused reductions in the size of Moina, cyclopoids and calanoids found. An increase in Daphnia size, 'gigantism', occurred because of limitations in the mouth gape of the fry. Low densities of fingerlings (0.65 g wet weight and stocked at 1 and 2 m-2) had little effect on zooplankton succession, whereas high density (15 fingerlings m-2) caused a shift to a zooplankton community dominated by small cladocerans, rotifers and cyclopoids. High fingerling density also caused a reduction in the size of the microcrustaceans found. The size and density of fish determined their impact on zooplankton composition and succession, demonstrating that similar starting times and consistency in fish density are necessary in obtaining 'sensible' statistical inferences in field fish-zooplankton experiments.