Sea ice decline drives biogeographical shifts of key Calanus species in the central Arctic Ocean

In recent decades, the central Arctic Ocean has been experiencing dramatic decline in sea ice coverage, thickness and extent, which is expected to have a tremendous impact on all levels of Arctic marine life. Here, we analyze the regional and temporal changes in pan-Arctic distribution and population structure of the key zooplankton species Calanus glacialis and C. hyperboreus in relation to recent changes in ice conditions, based on historical (1993–1998) and recent (2007–2016) zooplankton collections and satellite-based sea ice observations. We found strong correlations between Calanus abundance/population structure and a number of sea ice parameters. These relationships were particularly strong for C. glacialis, with higher numbers being observed at locations with a lower ice concentration, a shorter distance to the ice edge, and more days of open water. Interestingly, early stages of C. hyperboreus followed the same trends, suggesting that these two species substantially overlap in their core distribution area in the Arctic Ocean. Calanus glacialis and C. hyperboreus have been historically classified as shelf versus basin species, yet we conclude that both species can inhabit a wide range of bottom depths and their distribution in the Arctic Ocean is largely shaped by sea ice dynamics. Our data suggest that the core distribution patterns of these key zooplankton are shifting northwards with retreating sea ice and changing climate conditions.publishedVersio

Sea ice decline drives biogeographical shifts of key Calanus species in the central Arctic Ocean

publishedVersio

Abundance of the life stages of three Calanus species and selected other zooplankton during Polarstern cruise ARK-VIII/2 (PS19)

Abundances of the life stages of the three Calanus species (Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus) and of selected zooplankton was calculated in the Arctic Ocean during Polarstern cruise ARK-VIII/2. Samples were taken with the Bongo net (mesh size: 200 µm)

Zooplankton of the low-oxygen waters of Bahia Callao (Central Peru) - with special reference to the reproductive activity of the copepod Acartia tonsa

Zooplankton distribution in the Bahia Callao, a low oxygen bay in Central Peru, was studied during surveys in March (austral summer) and September (austral spring) 2006. In March temperature was higher, but oxygen concentrations were much lower, especially near the sea floor. Zooplankton abundance at 14 repeated stations (March/September = 457/2356 ind. m−3), taxa number (35/97), and community composition changed drastically, but Acartia tonsa was dominant during both surveys. In contrast, abundance of meroplanktonic larvae did not change. The reproductive activity of A. tonsa was studied bi-weekly from November 2005 to August 2007 at a fixed station close to shore (9 m water depth). Population egg production rate ranged from 0.9 to 12.6 eggs female−1d−1 and was significantly related to Chlorophyll a, temperature, and dissolved oxygen. Individual clutch size ranged from 1 to 43 eggs. Egg hatching rate varied from 3.4 to 100%; the lowest values were associated with very low concentrations of dissolved oxygen in the surface layer and red tides. In feeding experiments at saturated oxygen concentrations >30 eggs female−1d−1 were produced, indicating continuous inhibition of egg production in the field. Oceanographic data demonstrate that the bay, and probably also the adjacent shelves, are exposed to frequent environmental changes, which challenge the survival and production of zooplankton and fish. The relationship between seemingly adverse environmental conditions and high biological productivity still needs to be understood

Abundance of the life stages of three Calanus species during Polarstern cruise ARK-XIII/1a and ARK-XIII/2 (PS44)

Abundances of the life stages of the three Calanus species (Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus) and of selected zooplankton was calculated in the Arctic Ocean during Polarstern cruise ARK-XIII/1a and ARK-XIII/2. Samples were taken with the Multinet midi (Hydrobios, Kiel), which is equipped with five nets (mesh size: 150 µm)

A seasonal comparison of zooplankton communities in the Kara Sea – With special emphasis on overwintering traits

Siberian marginal seas cover large parts of the marine Arctic and host unique zooplankton communities. Detailed knowledge of their community structure and life history traits is a prerequisite to predict their response to ongoing and future climate and anthropogenic changes although winter data is extremely rare. Here data are presented from winter samples (February and April) in four biogeographic regions of the Kara Sea. Comparison of community composition and zooplankton abundance/biomass with data collected during summer showed lower diversity in winter, mainly due to the absence of freshwater species. In contrast to many other northern regions, seasonal biomass differences were relatively small. Year-round high biomass is maintained through a large share of small copepod species and constantly high share of the chaetognath Parasagitta elegans. An advanced state of gonad maturation and reproduction was observed in winter in herbivorous, omnivorous, and carnivorous species, e.g. the copepods Calanus glacialis, Drepanopus bungei, Limnocalanus macrurus, Oithona similis, Pseudocalanus major, Pseudocalanus minutus/acuspes, Paraeuchaeta glacialis, Microcalanus pygmaeus, and euphausiids, hydromedusae, and pteropods. Meroplanktonic larvae of nudibranchia, polychaeta and bivalvia were also registered. Close to the Yenisei mouth, abundance of eggs and larvae of various taxa exceeded older stages. Our data show that the brackish-water zone of the Kara Sea hosts specific communities with omnivorous species efficiently exploiting local resources during the winter and utilizing them for winter reproduction

Abundance of the life stages of three Calanus species and Metridia longa during Polarstern cruise ARK-XXVI/3 (PS78, TRANSARK)

Abundances of the life stages of the three Calanus species (Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus) and Metridia longa was calculated in the Arctic Ocean during Polarstern cruise ARK-XXVI/3. Samples were taken with the Multinet maxi (Hydrobios, Kiel), which is equipped with nine nets (mesh size: 150 µm)