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The shells of calcitic arthropod Amphibalanus improvisus; aragonitic bivalvesCerastoderma glaucum, Limecola balthica, and Mya arenaria; and bimineralic bivalve Mytilus trossulus were collected in the brackish waters of the southern Baltic Sea in order to study patterns of bulk elemental concentration (Ca, Na, Sr, Mg, Ba, Mn, Cu, Pb, V, Y, U and Cd) in shells composed of different crystal lattices (calcite and aragonite). The factors controlling the elemental composition of shells are discussed in the context of crystal lattice properties, size classes of organisms and potential environmental differences between locations. Clams that precipitate fully aragonitic shells have a clear predominance of Sr over Mg in shells, contrary to predominant accumulation of Mg over Sr in calcitic shells of barnacles. However, the barnacle calcite shell contains higher Sr concentration than bivalve aragonite. The elemental variability between size-grouped shells is different for each studied species, and the elemental concentrations tend to be lower in the large size classes compared to the smaller size classes. Biological differences between and within species, such as growth rate, feeding strategy (including feeding rate and assimilation efficiency or composition) and contribution of organic material, seem to be important factors determining the elemental accumulation in shells. Because specimens used in this study were obtained from different sampling sites within the gulf, the impact of location-specific environmental factors, such as sediment type, cannot be excluded.

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.

The establishment of baseline information on biodiversity is important as contemporary biodiversity might act as a bioindicator of environmental change. It is especially important at locations which are expected to be largely impacted by climate change, such as Icelandic waters. The present study focuses on the diversity of bryozoan species in Iceland. An Icelandic bryozoan species list was compiled from three main data sources: species collected during the BIOICE programme, species deposited in old museum collections and from literature. A total of 288 species were recorded from the study area, 67 of which are new records in Icelandic waters and three are potentially non-indigenous species. Such diversity is relatively high in comparison to other areas and yet predicted to be even higher if more studies were to be conducted. Encrusting forms (56%) were by far the most numerous among studied bryozoans. The highest number of species (71) was recorded in the shallowest 0–100 m zone which is most likely a result of complex factors including high primary productivity of that zone. This study reveals a large proportion of new species records for the area, showing how little is known about bryozoan diversity and its ecological aspects in such important areas as Icelandic waters. It is a starting point for further in-depth investigations of this specific group of organisms.

Mussels have the ability to control biomineral production and chemical composition, producing shells with a range of functions. In addition to biological control, the environment also seems to influence the process of biomineralization; thus, shells can be used as archives of ambient water parameters during the calcium carbonate deposition. Past and present environmental conditions are recorded in the shells in the form of various proxies including Mg/Ca or Sr/Ca ratios. For such proxies to be accurate and robust, the influence of biological effects including the size of studied organism must be examined and eliminated or minimized, so that the environmental signal can be efficiently extracted. This study considers mineralogy and elemental composition of shells representing four size classes of Mytilus trossulus from the Baltic Sea. Obtained results suggest that mineralogy and chemical composition change throughout the shell development due to most likely a combination of environmental and biological factors. The content of aragonite increases with increasing shell size, while the bulk concentrations of Na, Cd, Cu, U, V, Zn and Pb were found to decrease with increasing height of the shells. Therefore, using mussels for environmental monitoring requires analysis of individuals in the same size range.

Knowledge of environmental preferences of the key planktonic species, such as Calanus copepods in the Arctic, is crucial to understand ecosystem function and its future under climate change. Here, we assessed the environmental conditions influencing the development stages of Atlantic Calanus finmarchicus and Arctic Calanus glacialis, and we quantified the extent to which their niches overlap by incorporating multiple environmental data. We based our analysis on a 3-year seasonal collection of zooplankton by sediment traps, located on moorings in two contrasting Svalbard fjords: the Arctic Rijpfjorden and the Atlantic-influenced Kongsfjorden. Despite large differences in water temperature between the fjords, local realized ecological niches of the sibling Calanus species overlapped almost perfectly. The exception was the earliest copepodites of C. glacialis in Rijpfjorden, which probably utilized the local ice algal bloom in spring. However, during periods with no sea ice, like in Kongsfjorden, the siblings of both Calanus species showed high synchronization in the population structure. Interestingly, differences in temperature preferences of C. finmarchicus and C. glacialis were much higher between the studied fjords than between the species. Our analysis confirmed the high plasticity of Calanus copepods and their abilities to adapt to highly variable environmental settings, not only on an interannual basis but also in a climate warming context, indicating some resilience in the Calanus community.

The Arctic and Antarctic share many oceanographical features but differ greatly in their geological histories. These divergent aspects lead to similarities and differences between the sets of species inhabiting the poles. However, the patterns are not unambiguously homogenous throughout the tree of life. For the first time, Hydrozoa (Leptothecata and Anthoathecata) is used as a model group to study patterns of diversity, distribution, bathymetry and life history strategies between the polar regions. The analyses are based on a comprehensive literature survey of hydrozoan records. Subtle differences in species richness and contrasting values of endemism are found between the Antarctic (252 species and 58% endemics) and Arctic (233 species and 20% endemics) regions. Shared trends include the lack of a medusa stage in most of the representatives, a high percentage of rarity (Arctic: 49%; Antarctic: 63%), and few common species (18% in both regions). A few species (Grammaria abietina, Obelia longissima and Paragotoea bathybia) and genera (Bouillonia and Gymnogonos) might be tentatively considered bipolar, but further molecular investigation is recommended. The bathymetric distribution mirrors the geomorphological characteristics of each region. The highest species richness occurred in the continental shelves of both polar regions. Updated inventories from each polar region are provided as supplementary material. The present work establishes a fundamental step towards an integrated bipolar framework for the study of diversity and ecology of polar regions, laying the foundation for future approaches on a wide array of topics, from origin and diversification, to changes in the distribution of polar biota.

Body size is one of the most important biological characters, as it defines many aspects of organismal functioning at the individual and community level. As body size controls many ecological aspects of species, it is often used as a proxy for the status of the ecosystem. So far no consistent mechanism driving size shift has been proposed. In this study, we investigated bathymetric variability in zooid’s size and shape in aquatic colonial animals, Bryozoa. Although the response of bryozoan zooid size to temperature or food concentration has been experimentally proven, the effects of natural environmental variability on marine bryozoan populations has been much less explored. The presented investigation is aimed to assess the bathymetric patterns and environmental drivers of bryozoan zooid size on continental shelf and slope of southern Iceland. 196 colonies of 11 species representing different colonial forms and taxonomic groups were selected for zooid characteristics measurements. A pattern of depth-related increase in zooid size was documented for Bicellarina alderi , Chartella barleei and Sarsiflustra abyssicola , no statistically significant effects were detected for the other eight species. Two species Bicellarina alderi and Caberea ellisii had significantly longer zooids in deeper water, shape of the remaining species did not change along the bathymetric gradient. Intercolonial coefficient of variation in zooid size did not change across the depth gradient. Temperature differences along studied depth could be responsible for the observed pattern.

Thirty-two species of echinoderms from epibenthic sledges, dredges, scuba diving, and other samples (in total: 467 samples and 20 000 specimens) from fjords and coastal waters off Spitsbergen were analysed between 1996 and 2014. The most numerous group of echinoderms in the coastal waters off Spitsbergen is brittle stars (78% of the total individuals). The echinoderms do not form any clear assemblages according to depth or distance from glacial sedimentation and substrate. Some species prefer hard bottom ( ) or water free from glacial suspensions ( ). In contrast to the species listed above, we also found opportunistic species such as the starfish and the brittle star . These two species are distributed quite uniformly, regardless of the environmental factors. The majority of the species prefer a soft bottom below 200 m.

A growing body of evidence suggests that ocean acidification acting synergistically with ocean warming alters carbonate biomineralization in a variety of marine biota. Magnesium often substitutes for Ca in the calcite skeletons of marine invertebrates, increasing their solubility. The spatio-environmental distribution of Mg in marine invertebrates has seldom been studied, despite its importance for assessing vulnerabilities to ocean acidification. Because pH decreases with water depth, it is predicted that levels of Mg in calcite skeletons should also decrease to counteract dissolution. Such a pattern has been suggested by evidence from echinoderms. Data on magnesium content and depth in Arctic bryozoans (52 species, 103 individuals, 150 samples) are here used to test this prediction, aided by comparison with six conceptual models explaining all possible scenarios. Analyses were based on a uniform dataset spanning more than 200 m of coastal water depth. No significant relationship was found between depth and Mg content; indeed, the highest Mg content among the analyzed taxa (8.7 % mol MgCO 3 ) was recorded from the deepest settings (>200 m). Our findings contrast with previously published results from echinoderms in which Mg was found to decrease with depth. The bryozoan results suggest that ocean acidification may have less impact on the studied bryozoans than is generally assumed. In the broad context, our study exemplifies quantitative testing of spatial patterns of skeletal geochemistry for predicting the biological effects of environmental change in the oceans.