Search

Marine organisms living at high latitudes are faced with a light climate that undergoes drastic annual changes, especially during the polar night (PN) when the sun remains below the horizon for months. This raises the question of a possible synchronization and entrainment of biological rhythms under the governance of light at very low intensities. We analyzed the rhythms of the mussel Mytilus sp. during PN. We show that (1) mussels expressed a rhythmic behavior during PN; (2) a monthly moonlight rhythm was expressed; (3) a daily rhythm was expressed and influenced by both sunlight and moonlight; and (4) depending on the different times of PN and moon cycle characteristics, we were able to discriminate whether the moon or the sun synchronize the daily rhythm. Our findings fuel the idea that the capability of moonlight to synchronize daily rhythms when sunlight is not sufficient would be a crucial advantage during PN.

© 2016 Elsevier B.V. Understanding rapid climate change in the Arctic and its ecosystem implications requires more information on the environment at temporal resolutions and time-periods not available from instrumental records. Such information can be acquired through geochemical proxy records, but sub-annual records are rare. We analyzed shell material of bivalve mollusks (Serripes groenlandicus and Ciliatocardium ciliatum) placed on oceanographic moorings for one year in two Arctic fjords to assess the potential use of shell elemental ratios as environmental proxies. Li/Ca, Mg/Ca, Li/Mg, Li/Sr, Mn/Ca, Sr/Ca, Mo/Ca, and Ba/Ca were determined using Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry. Combining data from moorings with previously derived sub-annual shell growth models allowed us to relate the elemental ratio patterns to oceanographic parameters (temperature, salinity, and fluorescence). Shell Ba/Ca profiles were characterized by abrupt peaks occurring 11 to 81 days after the phytoplankton bloom, as indicated by an index of seawater fluorescence. Li/Ca and Mg/Ca values exhibited significant logarithmic relationships with shell growth rate, indicated by marginal R2 values of 0.43 and 0.30, respectively. These ratios were also linearly related to temperature, with marginal R2 values of 0.15 and 0.17, respectively. Mn/Ca and Sr/Ca ratios exhibited variability among individuals and their temporal pattern was likely controlled by several unidentified factors. Mo/Ca patterns within the shells did not demonstrate correlations with any of the oceanographic parameters. Our results reflect complex relationships between elemental ratios and bivalve metabolism, methodological limitations, as well as contemporaneous environmental processes, suggesting that none of the studied elemental ratios can be used as unequivocal proxies of seawater temperature, salinity, paleoproductivity, or shell growth rate. Despite this, Ba/Ca and Li/Ca can be used as sub-annual temporal anchors in further studies because the variability of these elements was synchronized in each fjord.

The Arctic Ocean faces rapid climate change, which impacts both physical and biological components of the marine ecosystem. Due to complicated and costly logistics inherent to sampling ice-covered areas, most studies conducted in the Arctic are based on relatively short-term sampling (weeks to months) centered around the minimum ice season. Given the need for longer-term monitoring, several autonomous ice-tethered observational platforms have been developed and deployed in the Arctic since the last decade. This review outlines their abilities, conception, and limitations. Most platforms were developed to measure physical data, which highlights a critical need for ice-tethered observatories monitoring biological processes.

The central Arctic Ocean is not isolated, but tightly connected to the northern Pacific and Atlantic Oceans. Advection of nutrient-, detritus- and plankton-rich waters into the Arctic Ocean forms lengthy contiguous domains that connect subarctic with the arctic biota, supporting both primary production and higher trophic level consumers. In turn, the Arctic influences the physical, chemical and biological oceanography of adjacent subarctic waters through southward fluxes. However, exports of biomass out of the Arctic Ocean into both the Pacific and Atlantic Oceans are thought to be far smaller than the northward influx. Thus, Arctic Ocean ecosystems are net biomass beneficiaries through advection. The biotic impact of Atlantic- and Pacific-origin taxa in arctic waters depends on the total supply of allochthonously-produced biomass, their ability to survive as adults and their (unsuccessful) reproduction in the new environment. Thus, advective transport can be thought of as trails of life and death in the Arctic Ocean. Through direct and indirect (mammal stomachs, models) observations this overview presents information about the advection and fate of zooplankton in the Arctic Ocean, now and in the future. The main zooplankton organisms subjected to advection into and inside the Arctic Ocean are (a) oceanic expatriates of boreal Atlantic and Pacific origin, (b) oceanic Arctic residents and (c) neritic Arctic expatriates. As compared to the Pacific gateway the advective supply of zooplankton biomass through the Atlantic gateways is 2–3 times higher. Advection characterises how the main planktonic organisms interact along the contiguous domains and shows how the subarctic production regimes fuel life in the Arctic Ocean. The main differences in the advective regimes through the Pacific and Atlantic gateways are presented. The Arctic Ocean is, at least in some regions, a net heterotrophic ocean that – during the foreseeable global warming trend – will more and more rely on an increasing local primary production while the advection of zooplankton, as revealed by models, will cease.

The Arctic ice cover poses severe limitations on the productive period of marine autotrophs that form the base of the marine food web. Sea-ice algae begin to grow in early spring within and underneath the ice, producing a substantial biomass despite very low light intensities. Pelagic algal blooms, in contrast, normally occur after ice breakup, at high latitudes as late as July–September. The timing of these blooms is crucial for the quantity and quality of primary and secondary production, and therefore for the transfer of energy and matter to higher trophic levels. Recent findings from Rijpfjorden, north-eastern Svalbard indicate that ice algae, rather than pelagic algae, trigger the reproduction of Arctic zooplankton around Svalbard. The key herbivore in Arctic shelf seas, the copepod Calanus glacialis, timed its seasonal migration, foraging, and reproduction to the ice algal bloom, which preceded the pelagic algal bloom by two months. The growth of this secondary producer’s offspring, however, was dependent on the later bloom of phytoplankton and higher sea-water temperatures. In 2007, reproduction and growth of C. glacialis and the primary production regime matched perfectly. The persistent ice cover in summer 2008, however, led to a mismatch between the pelagic algal bloom and the growth of the new copepod generation, resulting in a fivefold lower biomass of C. glacialis in August 2008 compared to 2007. The initiation of the ice algal bloom is mainly determined by the solar angle, whereas the pelagic algal bloom requires more light and is therefore governed to a larger degree by ice thinning and the unpredictable ice breakup. We conclude that both a too early as well as a too late ice breakup can cause a mismatch between primary and secondary producers, with negative consequences for the entire lipid-based Arctic marine food web.

Polar marine surface waters are characterized by high levels of dissolved oxygen, seasonally intense UV irradiance and high levels of dissolved organic carbon. Therefore, the Arctic sea-ice habitat is regarded as a strongly pro-oxidant environment, even though its significant ice cover protects the ice-associated ( = sympagic ) fauna from direct irradiation to a large extent. In order to investigate the level of resistance to oxyradical stress, we sampled the sympagic amphipod species Gammarus wilkitzkii during both winter and summer conditions, as well as exposed specimens to simulated levels of near-natural and elevated levels of UV irradiation. Results showed that this amphipod species possessed a much stronger antioxidant capacity during summer than during winter. Also, the experimental UV exposure showed a depletion in antioxidant defences, indicating a negative effect of UV exposure on the total oxyradical scavenging capacity. Another sympagic organism, Onisimus nanseni , was sampled during summer conditions. When compared to G. wilkitzkii , the species showed even higher antioxidant scavenging capacity.

The diel vertical migration (DVM) of zooplankton and pelagic fish in the southern Arctic Ocean (82°N) and in Rijpfjorden (Svalbard, Nordaustlandet, 80°N) was investigated in autumn 2004, when there were distinct differences in light conditions between day and night. We collected data on zooplankton and fish distribution using plankton nets, trawls, and an echo sounder together with data on environmental parameters including sea-ice distribution, hydrography, and in situ fluorescence in the water column. In Rijpfjorden, the Arctic phytoplankton bloom had culminated several weeks prior to the present study and all three Calanus species had migrated down to depths for over wintering and did not show any changes in vertical distribution. However, in the Arctic Ocean pack ice at 82°N, Calanus hyperboreus, was found in high abundances (up to 65 ind. m−3) actively feeding on the Arctic bloom in September. They performed a classic DVM, feeding in the upper 50 m during the night and descending to depths below 50 m during the day. In Rijpfjorden, distinct DVM patterns were observed among the amphipod Themisto libellula, adult and juvenile stages of the pteropod Limacina helicina, and polar cod. Polar cod in Rijpfjorden fed on Calanus spp. and on L. helicina. We conclude that animals display DVM in the Arctic during autumn if they need to feed in food-rich surface waters.

The genus Onisimus Boeck is divided into five species groups to be treated in this and forthcoming publications; a key to these groups includes the genera Menigrates Boeck and Paralibrotus Stephensen. Further keys and redescriptions are presented to all species within two Onisimus species groups. The O. brevicaudatus -group comprises the species O. affinis Hansen, 1886 (= O. dubius Schellenberg, 1935, syn. n.), O. botkini Birula, 1897, O. brevicaudatus Hansen, 1887, O. caricus Hansen, 1887, and O. derjugini Gurjanova, 1929. The O. sextonae -group consists of the species O. abyssi Oldevig, 1959, O. leucopis (G.O. Sars, 1879), and O. sextonae Chevreux, 1926. The full redescriptions of these species are provided in an accompanying Organisms Diversity and Evolution Electronic Supplement. See also Electronic Supplement at: http://www.senckenberg.de/odes/05-07.htm

The known associations between amphipods and echinoids are listed, separated into five different categories depending upon the nature of the associations. The new species Lepidepecreella andeep, found attached around the mouth of the cidarid sea urchin Aporocidaris antarctica, is described, as well as the new species Notopoma cidaridis. The tubes of the latter were found attached to the spines of the cidarid sea urchin Rhynchocidaris triplopora. These cases represent the first associations reported between amphipods and echinoids in the Antarctic. A key to both genera is provided.

Descriptions and figures of two new species of the genus Pseudo Berge & Vader, 2001 (Stegocephalidae: Stegocephalinae) are presented, but the two species are not given formal scientific names due to lack of material (both are only known by a single specimen each). However, the two new species have a significant impact on the classification and proposed phylogeny of the subfamily, as the two genera Pseudo Berge & Vader, 2001 and Schellenbergia Berge & Vader, 2001 now have to be considered synonymous. Pseudo is selected as the senior synonym. A discussion of the relationships among the genera of the subfamily Stegocephalinae is provided.

The monotypic genus Eclysis K.H. Barnard, 1932 and its type species, E. similis Barnard, are redescribed based upon a newly discovered second specimen. The genus Bathypanoploea Schellenberg, 1939 is reviewed; B. schellenbergi Holman & Watling, 1983 is fixed as the type species. Bathypanoploea polarsterni n. sp. is described; Alexandrella pulchra Ren in Ren & Huang, 1991 is a new junior synonym of B. schellenbergi. The morphology of Eclysis and Bathypanoploea is examined, as well as their relationships to the Astyridae and Stilipedidae.