Sea water temperature and light intensity at high-Arctic subtidal shallows - 16 years perspective.

Manifestations of climate change in the Arctic include an increase in water temperatures and massive loss of sea ice enabling more light penetration. Yet to understand tempo and scale of these parameters change over time, constant monitoring is needed. We present 16-yr long-term datasets of sea water temperature and relative light intensity at two depth strata (8 and 14 ± 1 m) of two hard-bottom sites in southern Isfjorden proper (Spitsbergen, 78°N). The high temporal resolution of the datasets (every 30 min, between 2006-2022) makes them suitable for studying changes at a local scale, correlating environmental variability with observed processes in benthic assemblages, and serving as ground-truth for comparison with, for example, remotely sensed or mooring data. These datasets serve as baseline for long-term investigations in the shallows of a high-Arctic fjord undergoing severe environmental changes.

Distribution of 137Cs in the marine environment from King George Island (Southern Shetlands, maritime Antarctica).

The article presents data on the activity of the radionuclide 137Cs in seawater, sediment, macroalgae, and zoobenthos from different locations in Admiralty Bay, King George Island, maritime Antarctica. The activity of 137Cs in the macrophytobenthos remained relatively stable across species, oscillating at the level of 1 Bq kg-1dw. However, a few individuals exhibited higher activity, particularly at stations closer to the glacier front. This result could have been caused by specific conditions resulting from melting glaciers and meltwater inflow and mixing with oceanic water. The activities of 137Cs in zoobenthic were in the range from 0.12 Bq kg-1dw (Asteroidea) to 24.2 Bq kg-1dw (Porifera) and the total doses in marine species were several orders of magnitude lower than reference levels. Stable isotopes of δ13C and δ15N suggest that the main factor influencing 137Cs activity may be the source of carbon (marine vs. terrestrial/glacial), rather than feeding strategy or trophic niches.

Assessing the present levels of 137Cs in the remote ecosystem of Bjornoya (South Svalbard).

The remoteness and small size of Bjornoya (S Svalbard) make the island one of the most unreachable places in the Arctic. Limited accessibility contributes to still-existing knowledge gap on isotope accumulation in compartments of its ecosystem. Therefore, in this study we aimed to investigate the current concentration of 137Cs in the terrestrial samples of vascular plants, cryptogams, and soil collected on Bjornoya in 2021. The measured average activity of 137Cs in bryophytes was 56.5 Bq kg-1, lichens 27.6 Bq kg-1, vascular plants 7.26 Bq kg-1, and soil 9.63 Bq kg-1. In the case of bryophytes, 137Cs activity was negatively correlated with δ15N. Our results suggest that bird guano was the main source of nitrogen and 137Cs for vascular plants. For bryophytes, significantly lower values of δ15N than in vascular plants suggests that this group is more sensitive to atmospheric N intake, with fallout being the main source of 137Cs.

Mercury and methylmercury in birds and marine mammals inhabiting the coastal zone of the two King George Island's bays: Admiralty and King George Bay (maritime Antarctic).

The Antarctic is particularly sensitive to mercury (Hg) pollution and even low levels of Hg may cause significant damage in this fragile environment. The aim of this study was to investigate routes of mercury and methylmercury (MeHg) elimination by animals inhabiting the maritime Antarctic. The results showed that organisms at the highest trophic level (elephant seal) have the highest concentrations of THg and MeHg in both excrement and fur samples. Interspecies differences in mercury levels were observed in materials sourced from penguins of the genus Pysgocelis.13C and 15N values confirmed differences in the diets and foraging areas, which may affect Hg concentration in the tissues we analyzed. Time variations in THg and MeHg concentrations were observed in the excrement of the penguin species, which may be due to periods of fasting and intense feeding closely related to egg laying and moulting stages.

Distribution of 90Sr and 137Cs in biotic and abiotic elements of the coastal zone of the King George Island (South Shetland Archipelago, Antarctic Peninsula).

For many years Antarctic ecosystems have been considered pristine, however recent studies, including our results, contradict this assumption. Our comprehensive study on the activity of anthropogenic radioisotopes (137Cs and 90Sr) in the most common species of green algae, bryophytes, lichens, and vascular plants, as well as soil and guano samples collected over a large area on King George Island (South Shetland Archipelago) in the austral summer 2018/2019 clearly indicate the importance of large-scale transport in shaping the level of pollution in areas very distant from potential sources of contamination. Additionally, radioisotope pollution can be measured even after a very long period (>60 years) since their occurrence. The mean activity of 137Cs measured in lichens, bryophytes, vascular plants, green algae, soil, and guano was, respectively: 3.72 Bq kg-1dw, 3.70 Bq kg-1dw, 2.62 Bq kg-1dw, 2.26 Bq kg-1dw, 4.07 Bq kg-1dw and 2.08 Bq kg-1dw. For 90Sr mean activity in lichens, bryophytes, vascular plants, green algae, and soil was, respectively: 1.99 Bq kg-1dw, 3.05 Bq kg-1dw, 2.42 Bq kg-1dw, 1.08 Bq kg-1dw, and 6.43 Bq kg-1dw. Increased activities of 90Sr and 137Cs were observed in species collected in the area influenced by glacier melt and penguin guano.

Mercury concentration and speciation in benthic organisms from Isfjorden, Svalbard.

Polar regions are an important part of the global mercury cycle and interesting study sites due to different possible mercury sources. The full understanding of mercury transformations in the Arctic is difficult because this region is the systems in transition -where the effects of the global climate change are the most prominent. Benthic organisms can be valuable bioindicators of heavy metal contamination. In July 2018, selected benthic organisms: macroalgae, brittle stars, sea urchins, gastropods, and starfish were collected in Isfjorden, Spitsbergen. Two of the sampling stations were located inside the fjord system and one at the entrance to the fjord. The results showed that the starfish were the most contaminated with mercury. Total mercury concentrations in these organisms were at least 10 times higher than in other organisms. However, they effectively deal with mercury by transporting it to hard tissue. The dominant form of mercury was the labile form.

Trophic markers and biometric measurements in Southern Ocean sea stars (1985-2017).

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 24,332 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 2,456 specimens of sea stars. Samples were collected between 12 January 1985 and 8 October 2017 in numerous locations along the Antarctic littoral and subantarctic islands. The spatial scope of the data set covers a significant portion of the Southern Ocean (47.717° S to 86.273° S; 127.767° W to 162.201° E; depth, 6-5,338 m). The data set 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 data set 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 data set, which is freely available without copyright restrictions.

Unexpected Levels of Biological Activity during the Polar Night Offer New Perspectives on a Warming Arctic.

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].

Evidence of season-dependency in vegetation effects on macrofauna in temperate seagrass meadows (Baltic Sea).

Seagrasses and associated macrophytes are important components of coastal systems as ecosystem engineers, habitat formers, and providers of food and shelter for other organisms. The positive impacts of seagrass vegetation on zoobenthic abundance and diversity (as compared to bare sands) are well documented, but only in surveys performed in summer, which is the season of maximum canopy development. Here we present the results of the first study of the relationship between the seasonal variability of seagrass vegetation and persistence and magnitude of contrasts in faunal communities between vegetated and bare sediments. The composition, abundance, biomass, and diversity of macrozoobenthos in both habitats were compared five times throughout the year in temperate eelgrass meadows in the southern Baltic Sea. Significant positive effects of macrophyte cover on invertebrate density and biomass were recorded only in June, July, and October when the seagrass canopy was relatively well developed. The effects of vegetation cover on faunal species richness, diversity, and composition persisted throughout the year, but the magnitude of these effects varied seasonally and followed changes in macrophyte biomass. The strongest effects were observed in July and coincided with maximums in seagrass biomass and the diversity and biomass of other macrophytes. These observations indicate that in temperate, clearly seasonal systems the assessment of macrophyte impact cannot be based solely on observations performed in just one season, especially when that season is the one in which macrophyte growth is at its maximum. The widely held belief that macrophyte cover strongly influences benthic fauna in marine coastal habitats, which is based on summer surveys, should be revisited and complemented with information obtained in other seasons.