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An endolithic lifestyle in mineralized substrates has evolved multiple times in various phyla including Bryozoa. The family Penetrantiidae includes one genus with ten extant and two fossil species. They predominantly colonize the shells of molluscs and establish colonies by chemical dissolution of calcium carbonate. Based on several morphological characters, they were described to be either cheilostome or ctenostome bryozoans. For more than 40 years, neither the characters of species identity and systematics nor the problem of their phylogeny was approached. Consequently, the aim of this study is to reevaluate species identities and the systematic position of the genus Penetrantia by analyzing at least six different species from eight regions with the aid of modern methods such as confocal laser scanning microscopy and 3D-reconstruction techniques. This study demonstrates that the musculature associated with the operculum and brood chamber shows significant differences from the cheilostome counterparts and seems to have evolved independently. Together with the presence of other ctenostome-like features such as true polymorphic stolons and uncalcified body wall, this finding supports a ctenostome affinity. Operculum morphology reveals many new species-specific characters, which, together with information about gonozooid morphology, tentacle number, and zooid size ranges, will enhance species identification. It also revealed a probable new species in Japan as well as potential cryptic species in France and New Zealand. In addition, this study increases the known distribution range of the family and its substrate diversity. Altogether, the new information collated here provides the basis for future work on a neglected taxon.

This is a phylogeographical study of Juxtacribrilina mutabilis, a recently described bryozoan from Japan with sightings in Sweden, Norway, and Maine (US), to test how fast and far it has expanded across Europe in recent years. J. mutabilis settles easily on ship hulls, making it a useful model organism for studying long-distance invasion pathways. The study was conducted using Autonomous Reef Monitoring Structures (ARMS) to monitor the entire European coastline and Svalbard for J. mutabilis using DNA metabarcoding. During the time between its first sighting in Europe 2008 and the last ARMS retrieval 2020, the data shows how J. mutabilis has gained a pan-European distribution, being genetically identified in 14 new distinct locations. Presence/absence of barcodes were confirmed by image-based identification in 74% of the samples. Fourteen haplotypes never reported before were discovered in a 264 bp region of the cytochrome oxidase I gene. Two haplotypes (HP1 and HP3) occurred frequently and geographically widely dispersed, indicating intercontinental connectivity. Two locations, Koster and Getxo showed particularly high genetic diversity with similar haplotype networks suggesting continuous gene flow across oceanographically unlinked regions. Given the recent description of J. mutabilis and the relatively few historical encounters, the genetic diversity described here suggests an unusually fast range expansion within the last two decades. Such global spreading events of fouling organisms may become more common in the future as a result of more frequent and interconnected ship traffic.

The Southern Ocean is showing one of the most rapid responses to human-induced global change, thus acting as a sentinel of the effects on marine species and ecosystems. Ocean warming and acidification are already impacting benthic species with carbonate skeletons, but the magnitude of these changes to species and ecosystems remains largely unknown. Here we provide the largest carbonate mineralogical dataset to date for Southern Ocean bryozoans, which are diverse, abundant and important as carbonate producers, thus making them excellent for monitoring the effects of ocean warming and acidification. To improve our understanding of how bryozoans might respond to ocean warming and acidification, we assess latitudinal and seafloor temperature patterns of skeletal mineralogy using bryozoan species occurrences together with temperature data for the first time. Our findings, combining new mineralogical data with published data from warmer regions, show that the proportions of high-Mg calcite and bimineralic species increase significantly towards lower latitudes and with increasing seawater temperature. These patterns are consistent with the hypothesis that seawater temperature is likely a significant driver of variations in bryozoan mineralogy at a global scale., The study was supported by National Science Centre Poland (project contracts 2016/23/B/ST10/01936 and 2021/40/C/ST10/00225). BF has received funding from the postdoctoral fellowships programme Beatriu de Pinós funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 programme of research and innovation of the European Union under the Marie Skłodowska-Curie grant agreement no. 801370 (Incorporation grant 2019 BP 00183). This work has been developed in the framework of MedCalRes project Grant PID2021-125323OA-I00 to BF funded by MCIN/AEI/10.13039/501100011033 and by ‘ERDF A way of making Europe'. With the institutional support of the ‘Severo Ochoa Centre of Excellence' accreditation (CEX2019-000928-S).

To understand the impact of anthropogenically induced transformations of biological communities, their naturally occurring fluctuation must be recognized first. Therefore, the aim of this study was to investigate the variability in Antarctic intertidal benthic assemblage faunal composition during an annual cycle (King George Island 62° S). Once a month, from December 2016 to November 2017, samples were collected at low-, mid- and high-tidal levels. Polychaetes were the most speciose group (15 species), followed by amphipods (12). Throughout the year, the most numerous taxa were gastropods (38% of the total number), followed by amphipods (23%) and bivalves (22%). The general pattern of the number of species and their abundance and biomass depended on the season and exhibited the highest values in austral autumn (April–June). Both species richness and abundance were highest in June and lowest in August. This study discovered that Antarctic intertidal macrofauna assemblages quickly respond to changes in environmental conditions and thus reflect seasonal climate fluctuations. The rapid development of these assemblages when the conditions are favourable proves their opportunistic and highly adaptable nature, which is potentially a good prognosis for survival in this ever-changing ecosystem.

The Antarctic Peninsula is undergoing rapid change due to global warming, including air and water temperature increases. Fauna inhabiting the intertidal zone are particularly exposed to warming impacts, as they are subjected to high variations in both terrestrial and marine environmental settings. This study aimed to assess intertidal macrofaunal and meiofaunal biodiversity, tidal height-related assemblage structural patterns and their responses to variability in environmental parameters on King George Island. A total of 39 macrofaunal taxa were identified, with polychaetes and amphipods being the most diverse groups and gastropods, amphipods and bivalves being the most abundant. In the case of meiofauna, 16 taxa were found, mainly nematodes, copepod nauplii and harpacticoids. There was a significant decrease in the number of species, abundance and biomass for both macrofauna and meiofauna with increasing tidal height. Our investigation documented highly diverse and abundant fauna in the Antarctic intertidal zone. With its thriving life, it could serve as a perfect model system for detecting climate change impacts on local biodiversity. Therefore, we propose the Antarctic intertidal zone as a suitable habitat for monitoring these changes.

Antarctic sea stars can occupy different trophic niches and display different trophic levels, but, while the impacts of their body size and environmental features on their trophic niches are potentially important, they are presently understudied. Here we assessed the trophic ecology in relation to the size and habitat of sea stars in a fjord on King George Island (South Shetland Islands) using stable isotope values of carbon (δ13C), nitrogen (δ15N), and sulphur (δ34S). The disc radius influenced δ13C and δ15N values, whereas more limited changes in δ13C or δ34S values were related to arm length. Specifically, δ13C and δ15N values were linked to disc radius in generalist species (Diplasterias brandti and Odontaster validus), which could indicate ontogenetic diet shifts, while this relationship occurred less frequently in more specialised species (Bathybiaster loripes, Notasterias bongraini, and Perknaster sladeni). O. validus had a smaller isotopic niche size in the inner than the outer fjord. The niche overlap between D. brandti and O. validus was low in the inner fjord. Low resource availability within the fjord, linked to higher turbidity, could induce trophic niche constriction and interspecific resource segregation. This could represent a mechanism for competition avoidance in a resource-limited system. Conversely, higher resource availability could allow O. validus to expand and share its isotopic niche with D. brandti in the outer fjord with a limited risk of competition. This trophic plasticity will likely influence how O. validus copes with the present and future modification of environmental conditions induced by climate change.

The Institute of Oceanology of the Polish Academy of Sciences (IO PAN) stores 77,500 natural history specimens from marine areas, which have been collected since 1985, when the Arctic Ecosystem Laboratory was established, later transformed into the Department of Marine Ecology. The majority of the collection is zooplankton (approximately 36,000 specimens) collected during the annual research cruises with the s/y Oceania ship to the area of the Nordic seas. Some smaller collections organized by individual researchers working with specific systematic groups are equally important. Thus, the Institutes collection resources also include specimens of bryozoans (Bryozoa), crustaceans (Crustacea) with a separate collection of hermit crabs (Paguroidea), as well as hydroids (Hydrozoa), bristle worms (Polychaeta), molluscs (Mollusca), sipunculid worms or peanut worms (Sipuncula), and echinoderms (Echinodermata) as well as protists (Protista), meiofauna with separate collections of kinorhynchs, the spiny-crown worms (Kinorhyncha) and nematodes (Nematoda) as well as Antarctic and Gulf of Gdansk macrofauna. As part of the IMBIO project (Integration and mobilization of data on the biotic diversity of Eukaryota in the resources of Polish scientific institutions), the specimen collections currently held by the Institute will be systematized and organized, and the data on resources will be digitalized in the form of metadata databases. The idea of digitizing the data contained in the descriptions of scientific collections and sharing them through the Polish Biodiversity Information Network (KSIB) and the Global Biodiversity Information Facility (GBIF) organizations will facilitate a wider insight and use of previously unavailable scientific collections.

The shells of calcitic arthropod Amphibalanus improvisus; aragonitic bivalves Cerastoderma 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.

Twenty-four Recent species of the boreal-Arctic and Pacific cheilostome bryozoan genus Rhamphostomella are described. The species R. tatarica and R. pacifica are transferred to Rhamphostomella from Posterula and Porella, respectively. Eight species are new: R. aleutica n. sp., R. aspera n. sp., R. commandorica n. sp., R. echinata n. sp., R. microavicularia n. sp., R. morozovi n. sp., R. multirostrata n. sp. and R. obliqua n. sp. Neotypes are selected for six species, and lectotypes for eight species. Mixtoscutella n. gen. is established for several Rhamphostomella-like species, including M. androsovae [formerly Smittina androsovae Gontar], M. cancellata [formerly Escharella porifera forma cancellata Smitt], M. harmsworthi [formerly Schizoporella harmsworthi Waters], M. ovata [formerly Cellepora ovata (Smitt)], and M. ussowi [formerly Schizoporella ussowi (Kluge)]. In addition to taxonomic revision, the morphology (frontal shields, ovicells and multiporous septula), ecology and zoogeography of these cheilostomes are discussed, and identification keys are presented. Most species of Rhamphostomella have broad bathymetric distributions. Some have long protuberances on their basal walls that allow them to grow elevated above allelopathically active substrates such as sponges. The diversity of Rhamphostomella peaks in the northwestern Pacific.

11 pages, 3 figures, 1 table, supplementary material https://doi.org/10.1126/sciadv.abm7452.-- Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper, the Supplementary Materials, Dryad, and Zenodo, Phylogenetic relationships and the timing of evolutionary events are essential for understanding evolution on longer time scales. Cheilostome bryozoans are a group of ubiquitous, species-rich, marine colonial organisms with an excellent fossil record but lack phylogenetic relationships inferred from molecular data. We present genome-skimmed data for 395 cheilostomes and combine these with 315 published sequences to infer relationships and the timing of key events among c. 500 cheilostome species. We find that named cheilostome genera and species are phylogenetically coherent, rendering fossil or contemporary specimens readily delimited using only skeletal morphology. Our phylogeny shows that parental care in the form of brooding evolved several times independently but was never lost in cheilostomes. Our fossil calibration, robust to varied assumptions, indicates that the cheilostome lineage and parental care therein could have Paleozoic origins, much older than the first known fossil record of cheilostomes in the Late Jurassic, This project is funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 724324 to L.H.L.). Extra funding for specific sampling expeditions were provided by the National Science Centre of Poland (grant PANIC/2016/23/B/ST10/01936 to P.K.), the ASSEMBLE Plus (Horizon 2020), the Leverhulme Trust (Research Project Award RPG-2016-429 to A.W.), the Russian Science Foundation (grant 18-14-00086 to A.N.O.), Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brazil [PQ-CNPq 308768/2018-3], Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil [FAPESP 19/17721-9] and the DISTANTCOM project (CTM2013-42667/ANT to C. Avila). B.F. was supported by Beatriu de Pinós (2019-BP-00183), funded by the AGAUR (Government of Catalonia) and by the Horizon 2020 programme under the Marie Skłodowska-Curie grant (no. 801370). The CAML-CEAMARC cruise of RV Aurora Australis (IPY project no. 53) were supported by the Australian Antarctic Division, the Japanese Science Foundation, the French Polar Institute IPEV, and the Muséum national d’Histoire naturelle, led by voyage leader, M. Riddle, With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S)

Sea stars (Echinodermata: Asteroidea) are a key component of Southern Ocean benthos, with 16% of the known sea star species living there. In temperate marine environments, sea stars commonly play an important role in food webs, acting as keystone species. However, trophic ecology and functional role of Southern Ocean sea stars are still poorly known, notably due to the scarcity of large-scale studies. Here, we report 24332 trophic marker (stable isotopes and elemental contents of C, N and S of tegument and/or tube feet) and biometric (arm length, disk radius, arm to disk ratio) measurements in 2456 specimens of sea stars. Samples were collected between 12/01/1985 and 08/10/2017 in numerous locations along the Antarctic littoral and Subantarctic islands. The spatial scope of the dataset covers a significant portion of the Southern Ocean (Latitude: 47.717° South to 86.273° South; longitude: 127.767° West to 162.201° East; depth: 6 to 5338 m). The dataset contains 133 distinct taxa, including 72 currently accepted species spanning 51 genera, 20 families and multiple feeding guilds / functional groups (suspension feeders, sediment feeders, omnivores, predators of mobile or sessile prey). For 505 specimens, mitochondrial CO1 genes were sequenced to confirm and/or refine taxonomic identifications, and those sequences are already publicly available through the Barcode of Life Data System. This number will grow in the future, as molecular analyses are still in progress. Overall, thanks to its large taxonomic, spatial, and temporal extent, as well as its integrative nature (combining genetic, morphological and ecological data), this dataset can be of wide interest to Southern Ocean ecologists, invertebrate zoologists, benthic ecologists, and environmental managers dealing with associated areas. Please cite this data paper in research products derived from the dataset, which is freely available without copyright restrictions.

Rhodolith beds and bioherms formed by ecosystem engineering crustose coralline algae support the northernmost centres of carbonate production, referred to as polar cold‐water carbonate factories. Yet, little is known about biodiversity and recruitment of these hard‐bottom communities or the bioeroders degrading them, and there is a demand for carbonate budgets to include respective rates of polar carbonate build‐up and bioerosion. To address these issues, a 10‐year settlement and bioerosion experiment was carried out at the Arctic Svalbard archipelago in and downslope of a rhodolith bed. The calcifiers recorded on experimental settlement tiles (56 taxa) were dominated by bryozoans, serpulids and foraminiferans. The majority of the bioerosion traces (30 ichnotaxa) were microborings, followed by attachment etchings and grazing traces. Biodiversity metrics show that calcifier diversity and bioerosion ichnodiversity are both elevated in the rhodolith bed, if compared to adjacent aphotic waters, but these differences are statistically insignificant. Accordingly, there were only low to moderate dissimilarities in the calcifier community structure and bioerosion trace assemblages between the two depth stations (46 and 127 m), substrate orientations (up‐ and down‐facing) and substrate types (PVC and limestone), in that order of relevance. In contrast, surface coverage as well as the carbonate accretion and bioerosion rates were all significantly elevated in the rhodolith bed, reflecting higher abundance or size of calcifiers and bioerosion traces. All three measures were highest for up‐facing substrates at 46 m, with a mean coverage of 78.2% (on PVC substrates), a mean accretion rate of 24.6 g m−2 year−1 (PVC), and a mean bioerosion rate of −35.1 g m−2 year−1 (limestone). Differences in these metrics depend on the same order of factors than the community structure. Considering all limestone substrates of the two platforms, carbonate accretion and bioerosion were nearly in balance at a net rate of −2.5 g m−2 year−1. A latitudinal comparison with previous settlement studies in the North Atlantic suggests that despite the harsh polar environment there is neither a depletion in the diversity of hard‐bottom calcifier communities nor in the ichnodiversity of grazing traces, attachment etchings and microborings formed by organotrophs. In contrast, microborings produced by phototrophs are strongly depleted because of limitations in the availability of light (condensed photic zonation, polar night, shading by sea ice). Also, macroborings were almost absent, surprisingly. With respect to carbonate production, the Svalbard carbonate factory marks the low end of a latitudinal gradient while bioerosion rates are similar or even higher than at comparable depth or photic regime at lower latitudes, although this might not apply to shallow euphotic waters (not covered in our experiment), given the observed depletion in bioeroding microphytes and macroborers. While echinoid grazing is particularly relevant for the bioerosion in the rhodolith bed, respective rates are far lower than those reported from tropical shallow‐water coral reefs. The slow pace of carbonate production but relatively high rates of bioerosion (both promoted by low carbonate supersaturation states in Arctic waters), in concert with high retention of skeletal carbonates on the seafloor and no calcite cements forming in open pore space created by microborers, suggest a low fossilisation potential for polar carbonates, such as those formed in the Mosselbukta rhodolith beds., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659

The impact of the rapidly changing Arctic on zooplankton community structure and seasonal behaviour is not yet understood. Here we examine 6 months of under-ice zooplankton observations from the N-ICE2015 expedition (January to June 2015) in the Nansen Basin and on the Yermak Plateau north of Svalbard. Stratified sampling in the water column was done with MultiNet during the entire expedition, and sampling in the upper 5 m below sea ice was performed during April-May by divers using a hand-held net. Hydrographic conditions were dominated by northward-flowing warm and saline Atlantic Water at intermediate depth, and southward-flowing cold Polar Surface Water in the upper 100 m. The mesozooplankton was dominated by copepods. Most numerous were the small ubiquitous Oithona similis in the upper 200 m, with Microcalanus spp. and Triconia borealis further down the water column. Calanus finmarchicus dominated among the Calanus species while Metridia longa was also numerous. The most abundant deep-water copepods were Paraeuchaeta spp. and Spinocalanus spp. Arrow worms (Chaetognatha) and comb jellies (Ctenophora) were the most numerous non-copepods. The mesozooplankton community was more dependent on surrounding water mass characteristics, such as salinity and depth, than geographical location. Algal food availability, which was closely linked to seasonality, explained the community changes seen in surface waters in May and June due to seasonal ascent and recruitment. Seasonal changes from winter to spring mostly involved an increase in the herbivorous C. finmarchicus and its nauplii in the upper 200 m of the water column coinciding with the peak of the phytoplankton bloom in late May. The Yermak Plateau and adjacent Nansen Basin were characterised by oceanic North Atlantic and Arctic species, many of which are deep water specialists. Despite the late onset of the spring bloom due to consolidated sea ice, both North Atlantic and Arctic species successfully reproduced in the study area. This explains the species-rich mesozooplankton community in this region as opposed to the less productive central Arctic Ocean. Future prospects of less sea ice and earlier onset of the bloom will likely be positive for the overall secondary production by both Arctic and boreal zooplankton in this region.

Non-indigenous species (NIS) in the Arctic have an increased likelihood of arrival from ship traffic in the region, while the survival potential of the species becomes more likely in a warming environment. Monitoring is essential to detect the rate and magnitude of the establishment of NIS. In this study, a list of 123 potential marine NIS for Svalbard was drafted and the presence of marine NIS in soft sediment of Kongsfjorden in Svalbard was assessed using molecular metabarcoding techniques. For 37 species, including eight potential Arctic NIS, we generated new 18S and/or COI barcode sequences to improve the available online reference databases. In total, 299 species were identified in the sediment samples, including seven potential NIS. Three of these potential NIS have not been reported before in Svalbard: the harpacticoid copepod Euterpina acutifrons, and the ascidians Botrylloides violaceus and Molgula manhattensis. Another novel observation for Svalbard was the polychaete Chone mollis. Additional studies are needed to assess whether the NIS have been established on Svalbard and what their potential impact on the local system may be. Metabarcoding proved to be an effective monitoring tool to detect the presence of new species in Svalbard marine waters. We advise its use to set up a baseline record for the presence of NIS at points of entry, especially harbours. This approach is also valuable for biodiversity monitoring, in particular the detection of small organisms and life stages that are hard to identify using current visual techniques.

In the Arctic, seasonal patterns in seawater biochemical conditions are shaped by physical, chemical, and biological processes related to the alternation of seasons, i.e. winter polar night and summer midnight sun. In summertime, CO2 concentration is driven by photosynthetic activity of autotrophs which raises seawater pH and carbonate saturation state (Ω). In addition, restriction of photosynthetic activity to the euphotic zone and establishment of seasonal stratification often leads to depth gradients in pH and Ω. In winter, however, severely reduced primary production along with respiration processes lead to higher CO2 concentrations which consequently decrease seawater pH and Ω. Many calcifying invertebrates incorporate other metals, in addition to calcium, into their skeletons, with potential consequences for stability of the mineral matrix and vulnerability to abrasion of predators. We tested whether changes in seawater chemistry due to light-driven activities of marine biota can influence the uptake of Mg into calcified skeletons of Arctic Bryozoa, a dominant faunal group in polar hard-bottom habitats. Our results indicate no clear differences between summer and winter levels of skeletal MgCO3 in five bryozoan species despite differences in Ω between these two seasons. Furthermore, we could not detect any depth-related differences in MgCO3 content in skeletons of selected bryozoans. These results may indicate that Arctic bryozoans are able to control MgCO3 skeletal concentrations biologically. Yet recorded spatial variability in MgCO3 content in skeletons from stations exhibiting different seawater parameters suggests that environmental factors can also, to some extent, shape the skeletal chemistry of Arctic bryozoans.

Large-scale climate changes influence the geographic distribution of biodiversity. Many taxa have been reported to extend or reduce their geographic range, move poleward or displace other species. However, for closely related species that can hybridize in the natural environment, displacement is not the only effect of changes of environmental variables. Another option is subtler, hidden expansion, which can be found using genetic methods only. The marine blue mussels Mytilus are known to change their geographic distribution despite being sessile animals. In addition to natural dissemination at larval phase&mdash, enhanced by intentional or accidental introductions and rafting&mdash, they can spread through hybridization and introgression with local congeners, which can create mixed populations sustaining in environmental conditions that are marginal for pure taxa. The Mytilus species have a wide distribution in coastal regions of the Northern and Southern Hemisphere. In this study, we investigated the inter-regional genetic differentiation of the Mytilus species complex at 53 locations in the North Atlantic and adjacent Arctic waters and linked this genetic variability to key local environmental drivers. Of seventy-nine candidate single nucleotide polymorphisms (SNPs), all samples were successfully genotyped with a subset of 54 SNPs. There was a clear interregional separation of Mytilus species. However, all three Mytilus species hybridized in the contact area and created hybrid zones with mixed populations. Boosted regression trees (BRT) models showed that inter-regional variability was important in many allele models but did not prevail over variability in local environmental factors. Local environmental variables described over 40% of variability in about 30% of the allele frequencies of Mytilus spp. For the 30% of alleles, variability in their frequencies was only weakly coupled with local environmental conditions. For most studied alleles the linkages between environmental drivers and the genetic variability of Mytilus spp. were random in respect to "coding" and "non-coding" regions. An analysis of the subset of data involving functional genes only showed that two SNPs at Hsp70 and ATPase genes correlated with environmental variables. Total predictive ability of the highest performing models (r2 between 0.550 and 0.801) were for alleles that discriminated most effectively M. trossulus from M. edulis and M. galloprovincialis, whereas the best performing allele model (BM101A) did the best at discriminating M. galloprovincialis from M. edulis and M. trossulus. Among the local environmental variables, salinity, water temperature, ice cover and chlorophyll a concentration were by far the greatest predictors, but their predictive performance varied among different allele models. In most cases changes in the allele frequencies along these environmental gradients were abrupt and occurred at a very narrow range of environmental variables. In general, regions of change in allele frequencies for M. trossulus occurred at 8&ndash, 11 psu, 0&ndash, 10 C, 60%&ndash, 70% of ice cover and 0&ndash, 2 mg m&minus, 3 of chlorophyll a, M. edulis at 8&ndash, 11 and 30&ndash, 35 psu, 10&ndash, 14 C and 60%&ndash, 70% of ice cover and for M. galloprovincialis at 30&ndash, 35 psu, 14&ndash, 20 C.

We report the ratios of minor (K/Ca, Na/Ca, P/Ca, S/Ca) and trace elements (Al/Ca, Ba/Ca, Fe/Ca, Mn/Ca and Zn/Ca) in skeletons of five Arctic echinoderm species representing three classes: Asteroidea, Ophiuroidea, Crinoidea. We found that skeletons of Arctic echinoderms show a unique, species-specific trace element composition that may suggest that incorporation of elements into the skeleton is biologically controlled by the organism. On the other hand, the concentration of some minor elements in skeletal parts exhibit patterns that are consistent with elemental concentrations in seawater, indicating that formation of echinoderm skeletons is environmentally controlled. Seawater is the main source of ions and compounds needed for skeletal formation and maintaining similar concentrations most likely reduces the biological cost related to selective uptake of ions. Additionally, Al, Ba, Fe, Mg and Mn showed station specific variation in elemental concentration which again suggests that accumulation of metals can be shaped by environmental concentrations.

The Antarctic sublittoral is one of the most demanding habitat for polar bottom-dwelling organisms, as the disturbance of this zone is highly intense. Rapid changes in the marine environment, such as increases in atmosphere and surface water temperatures, can cause dramatic changes in biodiversity, especially in glacial fjords affected by heavy melt water inputs from the retreating glaciers. In such areas, rocks are often an important support for local diversity, providing habitats for a number of encrusting organisms. Thus, understanding the patterns of diversity of shallow rock encrusting fauna and factors controlling it are particularly important. The structure and diversity patterns of rock encrusting fauna were examined from four ecologically contrasting sites in the shallow sublittoral (6–20 m) of Admiralty Bay (King George Island). The results revealed a rich and abundant encrusting community with bryozoans and polychaetes outcompeting representatives of other fauna such as foraminifera and porifera. Spatial variability in species composition, as well as biological parameters, revealed the trend of encrusting assemblages declining towards the inner fjord areas - strongly affected by high sediment input (species richness: 13.3 ± 1.2, and abundance: 68,932.99 ± 11,915.98 individuals m−2 ± standard error). In contrast, at sites more open to the central basin, a peak of biological parameters was observed (24.8 ± 1.4 and 297,360.9 ± 30,314.72, respectively). We suggest that increased sedimentation was the major factor structuring the encrusting assemblages in Ezcurra Inlet, masking the influence of other parameters, such as food and light availability, which are important for the distribution of epifauna. Thus, if the increasing intensity of glacial processes will continue in the upcoming years, the diversity of the encrusting fauna in the shallow sublittoral could dramatically decrease.

Kelp forests are complex underwater habitats that support diverse assemblages of animals ranging from sessile filter feeding invertebrates to fishes and marine mammals. In this study, the diversity of invertebrate fauna associated with kelp holdfasts was surveyed in a high Arctic glacial fjord (76 N, Hornsund, Svalbard). The effects of algal host identity (three kelp species: Laminaria digitata, Saccharina latissima and Alaria esculenta), depth (5 and 10 m) and glacier-derived disturbance (three sites with varying levels of mineral sedimentation) on faunal species richness and composition were studied based on 239 collected algal holdfasts. The species pool was mostly made up by three taxa: colonial Bryozoa and Hydrozoa, and Polychaeta. While the all-taxa species richness did not differ between depths, algal hosts and sites, the patterns varied when the two colonial sessile filter-feeding taxa were analysed alone (Hydrozoa and Bryozoa). The Hydrozoa sample species richness and average taxonomic distinctness were the highest at undisturbed sites, whereas Bryozoa species richness was higher in sediment-impacted localities, indicating relative insensitivity of this phylum to the increased level of mineral suspension in the water column. The average taxonomic distinctness of Bryozoa did not vary between sites. The species composition of kelp-associated fauna varied between sites and depths for the whole community and the most dominant taxa (Bryozoa, Hydrozoa). The high load of inorganic suspension and sedimentation did not cause pauperization of kelp holdfast-associated fauna but instead triggered the changes in species composition and shifts between dominant taxonomic groups.

The Mg/Ca and Sr/Ca ratios in echinoderm skeletal calcite are used as a proxy for Phanerozoic seawater changes, since the skeletal concentrations are, to some extent, controlled by environmental factors. However, it remains unclear how the influence of environmental factors is modified by vital effects, especially in polar waters. Therefore, the goal of this study was to compare the ratios of Mg/Ca and Sr/Ca among the skeletal parts of 10 common Arctic echinoderm species belonging to three classes Echinoidea, Asteroidea and Ophiuroidea that contribute substantially to the carbon cycle in the Arctic benthic system. Significant differences were recorded in echinoid skeletal element concentrations among specific skeletal parts. The lowest Mg/Ca and Sr/Ca ratios were detected in the spines (mean Mg/Ca 37.5 ± 8.8 SD; Sr/Ca 1.8 ± 0.1). The components of the Aristotle's lantern (epiphyses, pyramids and rotulas) were characterised by the highest Mg levels (Mg/Ca 79.9 ± 6.0; 75.2 ± 9.1; 60.1 ± 3.8, respectively). It is likely that mouth parts experience greater mechanical pressure compared to other body parts, and the higher content of Mg in the Aristotle's lantern contributes to its robustness. We did not find any distinctive trends in the distribution of skeletal elements in the asteroid and ophiuroid skeletal parts. The heterogeneous concentrations of Mg and Sr in different skeleton parts of the echinoids suggest possible physiological regulation of the chemical composition rather than the composition only being influenced by the environment. We cannot recommend echinoderm skeletons as reliable indicators in palaeoenvironmental reconstructions due to the possible biological control of skeletal chemistry, which may interfere with the effect of environmental variables.

Barnacles are widespread and abundant inhabitants of rock surfaces in the intertidal zone, providing considerable contributions to the formation of carbonate sediments. The main goal of this study was to test two hypotheses: (1) the chemical composition of the Balanus balanus shell is mostly controlled biologically, and environmental factors have only minor influences, and (2) the chemical composition of B. balanus shells does not vary with size. To test these hypotheses, samples were collected in two fjords from two depths. This study revealed site-related differences in shell chemistry, although no variability in shell chemical compositions was detected between the depths and among the size categories. Barnacle shell plates had different accumulation patterns for different trace elements (Mg, S, Sr), with the operculum as the most distinctive shell plate. As those plates are precipitated under the same environmental conditions, the different accumulation patterns may indicate biological control of element uptake in cirripedes. We suggest that the specific chemical composition of the operculum may be related to the required mechanical properties of this shell part, and thus, it is likely that this organism regulates accumulation patterns within its shell, because such regulation increases its adaptive properties. Our results supported both presented hypotheses.

For centuries, invertebrate collections have been subjected to various post-collection and curatorial cleaning techniques. Cleaning, however, may damage or even dissolve skeletal calcium carbonate and consequently influence any subsequent geochemical analysis. We investigated the combined effects of three cleaning variables: water (deionized and tap water), bleach (10% and 78%) and ultrasound (all for a range of durations), on the skeleton of Flustra foliacea (Linnaeus, 1758), a marine bryozoan. Treated and control carbonates were analysed both before and after cleaning, measuring: MgCO3 in calcite (X-ray diffractometry and staining); organic:inorganic carbon ratio, using elemental analysis for total carbon by combustion and for organic carbon by acid dissolution and combustion. Treatment solutions were analysed using inductively coupled plasma atomic emission spectroscopy (ICP-AES) to detect any Ca2 + and Mg2 + that may have leached out. Significantly more weight loss and removal of MgCO3 from calcite occurred in bleach concentrations of 10% or higher, especially in longer duration treatments and with use of ultrasound. Specimens with higher initial MgCO3 in calcite were especially susceptible to Mg leaching. We suggest that the interaction between bryozoan skeletal MgCO3 and cleaning solutions is controlled by a combination of solution chemistry and reaction kinetics, and that when cleaning specimens prior to geochemical analysis, less is better.

In this study, 235 measurements of magnesium concentration in echinoderm's skeletons were compiled, including 30 species and 216 specimens collected from northern and western Barents Sea. We aimed to reveal the scale of Mg variation in the skeletons of Arctic echinoderms. Furthermore, we attempted to examine whether the Mg concentration in echinoderm skeletons is determined primarily by biological factors or is a passive result of environmental influences. We found that the Mg concentration in echinoderm skeletons was characteristic for particular echinoderm classes or was even species-specific. The highest Mg contents were observed in asteroids, followed by ophiuroids, crinoids, and holothuroids, with the lowest values in echinoids. These results strongly imply that biological factors play an important role in controlling the incorporation of Mg into the skeletons of the studied individuals.

Photographic time-lapse techniques are especially useful in the marine realm for visualising long-term processes and remote monitoring of sites/objects/organisms where the presence of researchers m...

Understanding the population dynamics of benthic communities is impossible without understanding the processes related to their initial development, including recruitment. In polar areas, encrusting organisms, such as bryozoans, polychaetes, sponges and ascidians, are amongst some of the most species-rich and abundant groups of macrofaunal organisms, yet knowledge about their ecology is far from being complete. In this study, by investigating established encrusting assemblages and recruitment onto experimental substrate, we examine the level of similarity between adult populations and newly recruited assemblages in the polar realm. This study was conducted during the austral summer of 2010–2011 in Maritime Antarctica at King George Island (62°S, 58°W) at two locations contrasting in their biological and physical conditions. Despite the small distance (~3 km) between the two study sites, the local species pools (species composition, numerical abundance) differed significantly and had a great influence on the observed recruitment pattern. The species composition of new recruits overlapped with that of nearby assemblages at all examined locations. The dominance structure was also identical, with bryozoans being the major component of these assemblages. The numbers of species and individuals in the newly recruited communities and local resident assemblages were also strongly correlated. The obtained results suggest that the recruitment of encrusting fauna in the Antarctic can be very localized and occurs in close vicinity to adult populations.

In the high Arctic, recruitment of hard-bottom benthic organisms has been studied at single locations, but little is known about how it varies spatially or temporally, or how it is influenced by abiotic factors. In this study, settlement plates were simultaneously deployed at five locations in three Svalbard (Norway) fjords at depths ranging from 7 m to 215 m. Recruitment was significantly different among fjords and among locations within a fjord. Recruits at each site co-occurred randomly even though interspecific overgrowth was observed. This finding provides further evidence that there is not necessarily a relationship between non-random co-occurrence and interspecific competition, such as is traditionally assumed for other isolated, island-like habitats. We found significantly lower recruitment in an Arctic-influenced fjord than in more Atlantic-influenced fjords. The abundance and richness of recruits was significantly lower in fall-winter than in spring-summer, but the spirorbid Circeis armoricana recruited in high abundance in fall-winter. Both the abundance and taxonomic richness of recruits declined exponentially with depth, with the hydroid Stegopoma plicatile dominating at 215 m in an Atlantic-influenced fjord. The most abundant recruiting taxa (C. armoricana, Semibalanus balanoides, Harmeria scutulata, Celleporella hyalina) can be described as pioneer (early-succession) species. Crustose coralline algae, a slow-growing superior competitor, also recruited at one location. Recruitment in Svalbard is highly variable, both spatially and temporally, and our results show the influence of local factors such as adult species composition.

Environmental and biological factors play important roles in determining the skeletal morphology and mineralogy of modular colonial organisms such as bryozoans. The broad bathymetrical ranges of Antarctic bryozoans make them useful organisms for evaluating depth-related changes in colony morphology, including branch diameter, which has been shown to decrease with depth in various ramose colonial animals. The current study focuses on the bryozoan Fasciculipora ramosa, using 32 specimens collected at East Antarctica from 185 to 597 m deep during the CEAMARC cruise (2007–2008). In order to test for the expected inverse relationship between depth and branch diameter, measurements of branch diameters were made. Levels of Mg in the calcite skeleton were determined as this was also predicted to follow changes in branch diameter. A significant negative correlation was found between branch diameter and depth. No significant relationship was detected between branch diameter and skeletal Mg, suggesting that these variables are driven by different factors. The thickest branches were found in current-influenced sites on Adelie Bank where temperature and salinity are both lower and planktonic food supply may also be different from the other sites. Further studies are needed along a wider bathymetrical range to clarify which factors influence branch diameter as well as Mg content in F. ramosa and to test its potential as an environmental indicator.

Many studies have the aim of increasing our knowledge on settlement and colonization of epifauna. Despite broad interest these important processes have proved to be very complex and there are still issues which need more attention. Experiments presented here, performed in the Arctic, aim to explore colonization of epifauna on hard substrates in relation to: (1) site, (2) depth, and (3) substrate characteristics (i.e. heterogeneity and biotic/abiotic origin). Three different substrate types (pebbles, empty Buccinum undatum shells and artificial shells made of granite) were prepared and deployed on the seabed in four Arctic sites (two at Spitsbergen 78°N, two in Northern Norway 69°N) for one year. After recovery, epifaunal assemblage structure, species richness, abundance, and Shannon-Wiener diversity of each substrate was estimated, subjected to a three-factor fixed experimental design and analysed using permutational multivariate analysis of variance (PERMANOVA). As hypothesized, site (i.e. colonizer species pool, local environmental conditions) explained most of the variation, and proved to be most influential factor in determining epifaunal assemblage structure. However, where the spatial scale of investigation was lower, as at Spitsbergen where study sites were in close vicinity (2 nm apart), factors that varied with depth (e.g. macrofaunal cover) predominated. The study indicated that epifaunal assemblages are influenced to a different degree at various sites. Depending on the region (Spitsbergen or Northern Norway), the substrate surface area or substrate type were the least important factors, but still made some contribution. Results suggest also that among substrate features surface heterogeneity is of high importance, higher than its biotic/abiotic character. In most of the cases rough surfaces of artificial shells supported the highest species richness, abundance and diversity.

Thirty-two species of echinoderms from epibenthic sledges, dredges, scuba diving, and other samples (in total: 467 samples and c. 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 (Strongylocentrotus droebachiensis) or water free from glacial suspensions (Ophiopholis aculeata). In contrast to the species listed above, we also found opportunistic species such as the starfish Urasterias lincki and the brittle star Ophiocten sericeum. These two species are distributed quite uniformly, regardless of the environmental factors. The majority of the species prefer a soft bottom below 200 m.

In this study, the concentrations of 12 metals: Ca, Na, Sr, Mg, Ba, Mn, Cu, Pb, V, Y, U and Cd in shells of bivalve molluscs (aragonitic: Cerastoderma glaucum, Mya arenaria and Limecola balthica and bimineralic: Mytilus trossulus) and arthropods (calcitic: Amphibalanus improvisus) were obtained. The main goal was to determine the incorporation patterns of shells built with different calcium carbonate polymorphs. The role of potential biological control on the shell chemistry was assessed by comparing the concentrations of trace elements between younger and older individuals (different size classes). The potential impact of environmental factors on the observed elemental concentrations in the studied shells is discussed. Specimens were collected from brackish waters of the Baltic Sea (the Gulf of Gdansk). For every species, 40 individuals (ten in each size class) were selected. Pre-cleaned shells were analysed by ICP-OES and ICP-MS to determine the concentrations of metals. The distributions of elements both differ between species and exhibit high intraspecific variability. Calcitic shells preferentially incorporated Mg > Sr > Na, aragonitic shells incorporated Na > Sr > Mg, and bimineralic shells accumulated Na approximately two times more intensively, than Mg and Sr which remained at similar levels. Among all species, the calcitic shells of A. improvisus most effectively concentrated the majority of the studied elements, especially Mg > Mn > Ba, which was contrary to the shells of aragonitic molluscs that contained the lowest levels of trace elements. The size-dependent distributions of elements in shells did not exhibit a consistent pattern. The highest significant differences were found for the bimineralic shells of M. trossulus, while the smallest were found for aragonitic shells; if any variability occurred, it was observed in heavy metals (Pb, Cd). Our results indicate that elemental variability, especially that of Mg and Sr, is dominated by the properties of the crystal lattice. The inconsistent variability of trace element concentrations between species and within single populations supports the important role of species-specific biological control of the biomineralization process and indicates that environmental factors have a significant influence on the incorporation of trace elements into the shells.

This study provides taxonomic and distributional data of bryozoan species from the Ross Sea area, mainly around Terra Nova Bay, based on specimens curated at the Italian National Antarctic Museum (MNA, Section of Genoa). Bryozoan specimens were collected at 75 different sampling stations in the Ross Sea and in the Magellan Strait, in a bathymetric range of 18–711 meters, during 13 expeditions of the Italian National Antarctic Research Program (PNRA) conducted between 1988 and 2014. A total of 282 MNA vouchers corresponding to 311 specimens and 127 morphospecies have been identified and included in the present dataset. 62% of the species were already reported for the Terra Nova Bay area, where most of the Italian samples come from, with a 35% of samples representing new records classified at the specific level, and 3% classified at the genus level. These new additions increase to 124 the total number of species known to occur in Terra Nova Bay. Four 3D-models of Antarctic bryozoans from the Ross Sea are also presented and will be released for research and educational purposes on the Museum website.

The Southern Ocean is an important atmospheric carbon sink, and potential changes in the carbon flux in this region will affect the ocean as a whole. Thus, to monitor the variability of its physico-chemical parameters is becoming a priority. This study provides the first high-resolution all-year-round record of observed and computed physico-chemical data from a shallow coastal site in Terra Nova Bay (Ross Sea). From November 2018 to November 2019, an underwater observatory deployed at a 25 m depth under an ice pack recorded pressure (p), temperature (t), electrical conductivity (C), dissolved oxygen (DO), pH in total scale (pHT), and illuminance (Ev). Practical salinity (SP), density (ρ), tidal constituents, carbonate system parameters (total alkalinity (TA), carbon dioxide partial pressure (pCO2), calcite, and aragonite (ΩCa, ΩAr)), together with sea ice concentration (SIC) and chlorophyll-a (Chl-a), were derived from measured and satellite data. t, DO, and pHT displayed the lowest values between July and November (–1.95 °C, 6.61 mL L−1, 7.97) whereas the highest in January (+1.08 °C, 10.61 mL L−1, 8.35). SP had the lowest values (33.72 PSU) in February and the highest (34.87 PSU) in September. Ev peaked in March (201 lux), with the highest values (&gt, 50 lux) in correspondence to the lowest values of SIC and a delayed trend, between December and March, with respect to Chl-a values (0.2–1.1 mg m−3). ΩCa and ΩAr showed their highest average monthly values (±s.d.) in January (ΩCa: 3.41 ± 0.27, ΩAr: 2.14 ± 0.17), when DO had maximum values. The lowest Ω occurred in September (ΩCa: 2.11 ± 0.02, ΩAr: 1.32 ± 0.02), at the end of phytoplankton activity. No undersaturation for both calcite and aragonite was recorded during the study period. This study highlights that biological activities and physico-chemical variables of the investigated shallow coastal site are coupled and, in many cases, influence each other.

Ports are highly dynamic environments that are under substantial anthropogenic pressure generated by activities related to the fishery, transhipment of cargo and passenger traffic. Thus, seaports are exposed to physical disturbances, chemical pollution and biological invasions. Yet knowledge about biotic part and the influence of anthropogenic pressure on it in seaports often does not exist. The main aim of this study was to assess the biodiversity of the hard-bottom epifauna by examination of the course of the recruitment and succession processes in the poorly known port basin ecosystem of the southern Baltic Sea at the ports of Gdansk, Gdynia and Wladyslawowo. We wanted to test whether the different port areas had their unique species diversity and compositions. In all investigated ports we found relatively low biodiversity but high recruitment activity of sessile fauna. Six epifaunal species were observed, and Amphibalanus improvisus was consistently the dominant species (up to 47,126.5 ± 2747.1 SD individuals per 225 cm2 in July in Gdynia port). Seasonality was found to be the main factor shaping recruitment and further development of the sessile assemblages, and the seasonal sequences of epifaunal occurrence were similar in the three examined ports. Furthermore, the epifauna of all ports showed homogenous species richness, composition and abiotic characteristics, although in the Wladyslawowo port, which is more exposed to the open sea, a higher abundance of meroplankton and greater shares of accessory species (Mytilus spp., Limecola balthica, Cerastoderma glaucum and Mya arenaria) were found. The assemblage structures of the ports resembled those of nearby natural system (Gulf of Gdansk); thus, the port ecosystem seems to be an integral part of the surrounding natural habitat. Two years of monthly observations did not reveal any new non-native species in the examined study area.

Meroplankton comprise mainly of pelagic larvae of benthic invertebrates and play an important role as consumers and prey in coastal ecosystems. During a year-round study in Isfjorden (Svalbard Archipelago; >78°N), two locations (stations North and South) were sampled every third month to capture seasonal dynamics of meroplankton at high-latitudes, using different sampling methods (vertically hauled WP2 plankton net, and SCUBA diver-operated: horizontal towed net and underwater suction pump). Independent of sampling methods, seasonality was the factor that explained the largest part of variation in meroplankton composition (31.8%, PERMANOVA). Distinct seasonal abundance peaks were found of the following taxa: Polychaeta larvae and Cirripedia nauplii in spring; Bivalvia veligers, Echinodermata ophioplutei, and Cirripedia cypris during summer; while Bryozoa cyphonautes in autumn. These changes were driven mainly by water temperature, chlorophyll a concentration, and photoperiod, which according to DistLM routine, jointly explained 36.7% of meroplankton variability. Our results support the theory that planktotrophy is an important larval development strategy in some high Arctic taxa, e.g. Bivalvia and Cirripedia. We also observed that the southern part of Isfjorden was more productive and affected by the advection of Atlantic waters; while the northern location was influenced by the sea ice drift, coming from the north-eastern part of the Isfjord system in winter and spring, and was characterised by higher meroplankton abundances. The comparison of the number of taxa collected by each method and multivariate dispersion index between the standard WP2 plankton net and the remaining devices, operated by SCUBA divers, proved that WP2 is the most optimal method to collect meroplankton, especially from deeper waters. However, an underwater, manually operated suction pump would be a good choice in shallow coastal areas, especially with a dense kelp forest, where using a WP2 net is impossible. The joint use of the WP2 net and suction pump gives the highest value of multivariate dispersion index for the total community, as it additionally allows for the collection of demersal and epibenthic animals which are often omitted by standard net sampling methods, so this combination is worth recommending in studying shallow coastal ecosystems.

Recruitment pattern of benthic fauna in temperate marine ecosystems is still not well recognized, particularly in inland coastal seas with distinct environmental and ecological conditions. This study investigates the effect of natural surrounding community structure, environmental variables and substrate orientation on short-term recruitment of motile and sessile epibenthos in the southern Baltic Sea. Recruitment on topsurface and undersurface of Perspex panels deployed on the seafloor in a horizontal position was monitored monthly from March 2008 to March 2010 in two coastal habitats (sandy and gravelly) in the Gulf of Gdansk. Recruitment of epibenthic invertebrates took place primarily over a growing season (March–October) indicating that reproduction and settlement are driven by water temperature and gross primary production. Communities of recruits showed relatively homogenous spatial taxonomic composition but total epifaunal abundance varied between bottom types. Planktonic larvae supply and species-specific recruitment behaviour account primarily for settlement success, particularly on panel topsurface which hosted more diverse and more abundant recruits than panel undersurface. Relative to vertical substrates, horizontal panels had less numerous barnacle recruits probably due to inhibitory effect of sediment deposition and organic biofilm.