Ksenia Kosobokova

The reproductive cycle and life history of the Arctic copepod Calanus glacialis in the White Sea

Abstract Seasonal variations in the gonad development and sex ratio of copepodite stage V (CV) and adults were examined from February to November in order to understand the reproductive cycle and the life history of Calanus glacialis in the White Sea. Gonad maturation, sexual differentiation and moulting to adults take place during the 2nd year of development. Energy accumulation takes place in the spring and summer of the 2nd year. The following autumn/winter is the major period of CV maturation, which occurs independent of food supply. Maturation of males precedes that of females by 2–3 months. The maximum proportions of CV and adult males are found in the population in October and November. The onset of female maturation is observed in February and March, ca. 2 months prior to the spring phytoplankton bloom. Reproduction takes place between April and June. Its termination in the second half of June coincides with the warming of the surface water layer where egg laying takes place. Variations in the gonad morphology throughout the year suggest long life spans and iteroparity of females of C. glacialis in the White Sea. Many of them survive for several months after reproduction and are able to overwinter again. Therefore, females with different life histories co-occur in the population in winter: “young” females recently moulted from the overwintering CVs, and “old” females which have spawned at least once in their life, after which they return to overwintering conditions. In contrast, males have shorter life spans of 3–4 months resulting in a sex ratio skewed toward females at all seasons.

Composition and distribution of zooplankton in the Laptev Sea and adjacent Nansen Basin during summer, 1993

Abstract Zooplankton composition and distribution were investigated on the Laptev Sea shelf, over the continental slope and in the adjacent deep Nansen Basin during the joint German-Russian expedition “Arctic 93” with RV Polarstern and Ivan Kireyev in August/September 1993. In the shelf area biomass decreased from west to east with the lowest values in the area influenced by the Lena river runoff. A gradual increase of biomass from the shallow to the deep area correlated with water depth. Total biomass ranged between 0.1 and 1.5 g m−2 on the shelf and 4.7 and 7.9 g m−2 in the adjacent Nansen Basin. On the shelf Calanus glacialis/finmarchicus dominated overall. The contribution of brackish-water taxa was low in the west, where high salinity and southward currents from the Arctic Basin supported a marine neritic community, but on the southern and eastern Laptev shelf, in the areas of freshwater influence, brackish-water taxa contributed up to 27% of the total biomass. On the slope and in deep areas a few large Arctic copepod species, Calanus glacialis, C. hyperboreus and Metridia longa, composed the bulk of biomass and determined the pattern of its vertical distribution. The export of Calanus species from the Nansen Basin onto the Laptev shelf appears to be of great importance for the shelf communities. In turn, the eastern outer shelf and slope area of the Laptev Sea are thought to have a pronounced effect on the deep basin, modifying the populations entering the central Arctic.

Unexpected Levels of Biological Activity during the Polar Night Offer New Perspectives on a Warming Arctic

The current understanding of Arctic ecosystems is deeply rooted in the classical view of a bottom-up controlled system with strong physical forcing and seasonality in primary-production regimes. Consequently, the Arctic polar night is commonly disregarded as a time of year when biological activities are reduced to a minimum due to a reduced food supply. Here, based upon a multidisciplinary ecosystem-scale study from the polar night at 79°N, we present an entirely different view. Instead of an ecosystem that has entered a resting state, we document a system with high activity levels and biological interactions across most trophic levels. In some habitats, biological diversity and presence of juvenile stages were elevated in winter months compared to the more productive and sunlit periods. Ultimately, our results suggest a different perspective regarding ecosystem function that will be of importance for future environmental management and decision making, especially at a time when Arctic regions are experiencing accelerated environmental change [1].

Reproduction of Calanus glacialis in the Laptev Sea, Arctic Ocean

Abstract Abundance and reproductive biology (gonad maturation and egg production) of the Arctic copepod Calanus glacialis were studied in the Laptev Sea and adjacent Arctic Ocean in September 1993 and from July to September 1995. Both abundance and reproductive activity were subject to strong spatial and seasonal variability, which was related to the ice cover, feeding conditions and circulation pattern. Maximum abundance of the C. glacialis population was generally confined to the outer shelf and slope with depths between 50 and 1000 m. During both cruises, highest egg production rates and largest number of young copepodite stages were observed in the eastern Laptev Sea, where the development of the C. glacialis population seems to follow the opening of the “Siberian Polynya”. In the western part, which is usually covered by pack ice, females were all immature, and no young stages were found. However, females responded quickly to a temporary opening of the ice there in 1995 and spawned. Starvation experiments showed that food-independent reproduction fuelled by internal energy resources was at least partly responsible for relatively high egg production rates at low ambient food concentrations. Egg production rates in starved females were considerably higher than those previously reported.

Biodiversity and Biogeography of the Lower Trophic Taxa of the Pacific Arctic Region: Sensitivities to Climate Change

The lower trophic level taxa underpin the marine ecosystems of the Pacific Arctic Region (PAR). Recent field observations indicate that range shifts, and changes in the relative abundance of particular taxa have occurred within the last decade. Here we provide a region wide survey of the diversity and distribution of viruses, bacteria, archaea, auto- and heterotrophic protists, as well as metazoan zooplankton and benthic organisms in the PAR. Our aim is to provide a foundation for the assessment of the changes within the lower trophic level taxa of the PAR and to document such change when possible. Sensitivities to the effects of climate change are also discussed. Our vision is to enable data-based predictions regarding ecological succession in the PAR under current climate scenarios, and to deepen our understanding regarding what the future holds for higher trophic level organisms and the carbon cycle.

Inter-annual variability of summer mesozooplankton communities of the western Chukchi Sea: 2004–2012

The Chukchi Sea shelf is a complex transition zone between the Pacific and Arctic Oceans, on which climate variation may have a profound impact. We examined summer zooplankton community structure of the western Chukchi Sea in Alaskan and Russian waters during 2004, 2009, 2010 and 2012 within the ongoing Russian-American Long-term Census of the Arctic program. The four study years were very different both in water mass properties and in zooplankton community structure. A “warm” year with an early ice retreat and highest water temperatures occurred in 2004, whereas the years 2009–2012 were “cold” with a later-than-average ice retreat and colder average water temperatures during the sampling period. The extent and prominence of different water masses (Bering Sea–Anadyr Water, Alaska Coastal Current, Siberian Coastal Current, Resident Chukchi Water) within the Chukchi Sea varied between years, which was in turn reflected within the zooplankton communities. Community structure was highly correlated with water mass properties, with bottom temperature being the most significant factor influencing communities. The “cold” summers of 2009–2012 had nearly twice the biomass and abundance of zooplankton compared with the “warm” summer of 2004. Biomass was dominated by the large copepod Calanus glacialis believed to originate from the Bering Sea, and abundance was dominated by small shelf species of copepods, such as Pseudocalanus spp., Acartia spp. and Oithona similis. We discuss the implications of the inter-annual variability of planktonic communities within the Chukchi Sea and the possible effects of longer-term climate change.

Arctokonstantinus hardingi (Copepoda, Calanoida, Arctokonstantinidae): New family, new genus, and new species from the bathypelagial Arctic Basin

Abstract Arctokonstantinus hardingi is based on a female specimen collected at bathypelagic depths in the Arctic Ocean. The new family has similarities with the family Spinocalanidae (superfamily Spinocalanoidea); however, it does not fit well the diagnosis of the superfamily and family in length of antennule, setation of mandible and maxillule, significantly deviating morphology of maxilla and maxilliped and segmentation of P 1 exopod. Probably the new family represents a new calanoid superfamzly; however, until the male is known the species it is tentatively placed into the superfamily Spinocalanoidea. Arctokonstantinidae is attributed to the Spinocalanoidea based on segmentation and setation pattern of swimming legs P2-P4 and antennule structure. Relying on mouth-part morphology Arctokonstantinus could be considered a predator.

Genetics redraws pelagic biogeography of Calanus

Planktonic copepods of the genus Calanus play a central role in North Atlantic/Arctic marine food webs. Here, using molecular markers, we redrew the distributional ranges of Calanus species inhabiting the North Atlantic and Arctic Oceans and revealed much wider and more broadly overlapping distributions than previously described. The Arctic shelf species, C. glacialis, dominated the zooplankton assemblage of many Norwegian fjords, where only C. finmarchicus has been reported previously. In these fjords, high occurrences of the Arctic species C. hyperboreus were also found. Molecular markers revealed that the most common method of species identification, prosome length, cannot reliably discriminate the species in Norwegian fjords. Differences in degree of genetic differentiation among fjord populations of the two species suggested that C. glacialis is a more permanent resident of the fjords than C. finmarchicus. We found no evidence of hybridization between the species. Our results indicate a critical need for the wider use of molecular markers to reliably identify and discriminate these morphologically similar copepod species, which serve as important indicators of climate responses.

Population structure and production of four sibling species of Pseudocalanus spp. in the Chukchi Sea

Copepods of the genus Pseudocalanus are important members of zooplankton communities in temperate and polar shelf regions, but few studies have focused on their species-specific biology due to the very subtle morphological differences between the species. We assess the distribution, population structure and production of four co-occurring species of Pseudocalanus across the Chukchi Sea during 2004, 2009 and 2012. Our approach used a combination of microscopic identification and species-specific polymerase chain reaction to discriminate between the species. Currently, the arctic P. acuspes dominates the genus (50–90%), with the relative distribution of species closely linked to water mass distribution and variations in physical properties, making Pseudocalanus important indicators of water mass origin. Although the temperate P. newmani had a significant presence throughout the Chukchi Sea, its stage distribution suggests that they recruit poorly in cold waters. Direct temperature-manipulation experiments further suggest that the reproductive activity of the two temperate species is inhibited at low temperatures, while the arctic P. acuspes exhibits reduced fitness and lower reproductive capacity when temperatures are increased to 10°C. Our results suggest that shifting oceanographic patterns and climate warming will have unequal impact on this genus, arising from species-specific differences in life histories and tolerance to environmental conditions.

Zooplankton of the White Sea: Communities’ Structure, Seasonal Dynamics, Spatial Distribution, and Ecology

A comprehensive review of the state-of-the art knowledge on structure, ecology, and distribution of zooplankton communities of the White Sea is provided. Based on the detailed species inventory and understanding of the zoogeographical origin of the planktonic fauna of the White Sea, a comparison of zooplankton communities of different regions and bays of the White Sea is presented for the first time. Standard sampling techniques allowed assessment and comparison of zooplankton abundance and biomass for different sea regions. Patterns of the horizontal distribution of zooplankton, as well as seasonal and long-term variation of the zooplankton structure and biomass, are discussed. Life cycle strategies and ecology of key zooplankton species along with major features of phenology are described. Data presented here may serve as baseline information for monitoring the structure and productivity of the White Sea zooplankton communities in the future and under ongoing climate change.