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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]., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

This is the first attempt to compile a comprehensive and updated species list for Hydrozoa in the Arctic, encompassing both hydroid and medusa stages and including Siphonophorae. We address the hypothesis that the presence of a pelagic stage (holo- or meroplanktonic) was not necessary to successfully recolonize the Arctic by Hydrozoa after the Last Glacial Maximum. Presence-absence data of Hydrozoa in the Arctic were prepared on the basis of historical and present-day literature. The Arctic was divided into ecoregions. Species were grouped into distributional categories according to their worldwide occurrences. Each species was classified according to life history strategy. The similarity of species composition among regions was calculated with the Bray-Curtis index. Average and variation in taxonomic distinctness were used to measure diversity at the taxonomic level. A total of 268 species were recorded. Arctic-boreal species were the most common and dominated each studied region. Nineteen percent of species were restricted to the Arctic. There was a predominance of benthic species over holo- and meroplanktonic species. Arctic, Arctic-Boreal and Boreal species were mostly benthic, while widely distributed species more frequently possessed a pelagic stage. Our results support hypothesis that the presence of a pelagic stage (holo- or meroplanktonic) was not necessary to successfully recolonize the Arctic. The predominance of benthic Hydrozoa suggests that the Arctic could have been colonised after the Last Glacial Maximum by hydroids rafting on floating substrata or recolonising from glacial refugia.

This study compared the diversity parameters and structures of encrusting assemblages in two habitats situated at two levels of shallow rocky shore: hydrolittoral and littoral along the Baltic Sea system. We investigated the variability and level of distinctiveness of the hydrolittoral encrusting fauna based on species biodiversity and distribution, and compared these features with those of communities inhabiting the adjacent shallow littoral zone (3-m depth). Structural similarities and differences between the encrusting assemblages from adjacent hydrolittoral and littoral zones were studied within 14 locations distributed along the northern coastline of the Baltic Sea. Multivariate analysis indicates that salinity had the greatest influence on the structure of the investigated assemblages. Most of the observed hydrolittoral assemblages contained the same species as the littoral zone. This result indicated a shared common species pool with similar large-scale patterns of species distributions with some variability in the dominating species between zones. The similarity between species composition of the hydrolittoral and littoral assemblages decreased with increase of salinity. Additionally, with higher species richness and the occurrence of marine specialists adapted to hydrolittoral conditions, the role of the rock size in the frequency of species occurrence and assemblage diversity was less significant. [ABSTRACT FROM AUTHOR]

Hydroid diversity and species composition were studied in Arctic coastal waters around the Norwegian Svalbard Archipelago. The aim of the present study was to examine the influence of physical factors (depth and substrate type) on the distribution and diversity of the benthic hydrozoan fauna that has been poorly studied in the high-latitude polar region. The study is based on a total of 557 samples collected between 1996 and 2007. Over 1200 colonies and 70 taxa of Hydrozoa were collected by SCUBA divers, dredges and van Veen grabs. The distribution patterns with respect to major environmental factors were studied based on presence/absence data. Four substrate types were most commonly colonized by hydroid colonies: algae, bryozoans, rocks and hydrozoans. The highest species richness was noted on algae and rocks. Shallow water communities of the study area were characterized by a high hydroid species richness. A number of species decrease along the depth gradient. Some species have shown some preferences towards selected substrates or one of the two depth zones, but most hydroid species were generalists in terms of both the depth and substrate preferences. No species could be classified as substrate-specific ( i.e. occurring only on one substrate type). The substrate heterogeneity was shown to be an important driver of hydroid species richness in Arctic coastal waters. [ABSTRACT FROM AUTHOR]

The article presents information on a study which investigated the structure of subtidal and intertidal assemblages in Arctic versus temperate boulder shores. It examines adult community structure to explore levels of similarity among marine assemblages of Arctic intertidal zones compared with those in adjacent subtidal areas. It shows the values of densities of the most abundant species in the given site in intertidal and subtidal boulder-fields from temperate North Atlantic. It also describes a suggested model of intertidal boulder-fields assemblage regulation.

Bryozoans are one of the major macrofaunal groups of the high polar regions. Here we present data on the nature of bryozoan assemblages in the Svalbard Archipelago sampled over 6 years between 1997 and 2002. Samples were collected with use of Van Veen grab, dredge and Scuba diving at depths ranging from 0 to 268 m. Among examined material (5026 items) bryozoans were present on one type of abiotic (stones) and 40 types of biotic substrata. The biotic substrata we investigated included algae (12 taxa) and invertebrates (28 taxa: Hydrozoa, Gastropoda, Bivalvia, Polychaeta, Crustacea, Ascidiacea, other Bryozoa), Both a priori ANOSIM (Global R=0.512, P=0.001) and cluster analyses reveal differences between the assemblages on different types of substrata. Cluster analyses distinguish two distinct groups of substrata. The first (stable) included stones, molluscs and Balanus balanus whilst the second (flexible) consisted of algae, hydrozoans and bryozoans. Bryozoan assemblages which colonized different substrata, varied in terms of species composition and their dominance. Bryozoan species were categorized as generalists, low-specificity epibiotic species or locally abundant background species. No species were found to be substratum-specific to any type. Among substrata with the richest bryozoan fauna were stones (156 taxa), Chlamys idandica (68) and Balanm halaiim (62). There were clear pattems in the distribution of substrata colonized by bryozoans within the fjord system: those shallow near the mouth were rich whilst those in deeper water were depauperate. We consider environmental gradients such as siltation and processes related to depth to be responsible for such patterns. [ABSTRACT FROM AUTHOR]