Several aquatic top predators suffer from deficiency in vitamin B1 (thiamine), sometimes combined with low levels of carotenoid pigments, e.g., astaxanthin. The mechanisms leading to correlations between carotenoid pigmentation and thiamine status are not known. These substances and their precursors are produced by single-celled organisms and transferred to higher trophic levels via zooplankton. However, little is known about the factors regulating this transfer process and how it is affected by environmental stressors and zooplankton diet. We therefore exposed a common copepod, Temora longicornis, to ultraviolet radiation (UVR), which is an important environmental stressor, and to food items of different quality in terms of carotenoid profile. Astaxanthin was the most abundant carotenoid found in copepods. Its concentrations were negatively affected by UVR regardless of diet type, and the availability of an astaxanthin precursor (beta-carotene) in the diet did not affect the response. Thiamine, on the other hand, showed a varying response, with elevated levels in copepods exposed to UVR at low beta-carotene diet and lower levels in copepods exposed to UVR and high beta-carotene diet. Altogether, this indicates that astaxanthin was consumed for photoprotection in the zooplankton and that thiamine dynamics might be modulated by UVR under certain dietary conditions. Hence, the concentrations of astaxanthin and thiamine in copepods are dynamic and to some extent regulated by exposure to UVR. Thus, the ability of zooplankton to transfer these substances to higher trophic levels depends, to some extent, on the exposure to environmental stressors.

Zooplankton are crucial for food webs and biogeochemical cycles. However, warming associated with climatechange may alter their seasonal timing and reproductive strategies. This study investigated how long-termwarming impacted zooplankton (mainly copepods) phenology and overwintering strategies by comparing a Bal-tic Sea bay, heated by warm water discharge for more than 50 yr, with an unaffected control bay. Field observa-tions showed that copepod and phytoplankton population growth began earlier in the heated bay than in thecontrol bay, suggesting that copepod abundance was driven by both temperature and food availability in theheated bay and by a stronger temperature dependence in the control bay. Resting eggs are normally producedas a life-history strategy to survive unfavorable environmental conditions. Our laboratory incubation experi-ment showed fewer dormant resting eggs hatched from the heated bay sediment compared with the controlbay, supporting an evolutionary change in overwintering strategy. In conclusion, the results seemed to suggestthat copepods adjusted their life-history in elevated temperatures by relying less on the strategy of usingsediment-stored dormant eggs and instead started their spring development earlier, when phytoplankton foodwas available. Hence, this study suggests that climate change can shift copepod overwintering strategies, leadingto potential cascading effects in the food web and affecting overall biodiversity and productivity.

This Assessment Update by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) addresses the interacting effects of changes in stratospheric ozone, solar ultraviolet (UV) radiation, and climate on the environment and human health. These include new modelling studies that confirm the benefits of the Montreal Protocol in protecting the stratospheric ozone layer and its role in maintaining a stable climate, both at low and high latitudes. We also provide an update on projected levels of solar UV-radiation during the twenty-first century. Potential environmental consequences of climate intervention scenarios are also briefly discussed, illustrating the large uncertainties of, for example, Stratospheric Aerosol Injection (SAI). Modelling studies predict that, although SAI would cool the Earth's surface, other climate factors would be affected, including stratospheric ozone depletion and precipitation patterns. The contribution to global warming of replacements for ozone-depleting substances (ODS) are assessed. With respect to the breakdown products of chemicals under the purview of the Montreal Protocol, the risks to ecosystem and human health from the formation of trifluoroacetic acid (TFA) as a degradation product of ODS replacements are currently de minimis. UV-radiation and climate change continue to have complex interactive effects on the environment due largely to human activities. UV-radiation, other weathering factors, and microbial action contribute significantly to the breakdown of plastic waste in the environment, and in affecting transport, fate, and toxicity of the plastics in terrestrial and aquatic ecosystems, and the atmosphere. Sustainability demands continue to drive industry innovations to mitigate environmental consequences of the use and disposal of plastic and plastic-containing materials. Terrestrial ecosystems in alpine and polar environments are increasingly being exposed to enhanced UV-radiation due to earlier seasonal snow and ice melt because of climate warming and extended periods of ozone depletion. Solar radiation, including UV-radiation, also contributes to the decomposition of dead plant material, which affects nutrient cycling, carbon storage, emission of greenhouse gases, and soil fertility. In aquatic ecosystems, loss of ice cover is increasing the area of polar oceans exposed to UV-radiation with possible negative effects on phytoplankton productivity. However, modelling studies of Arctic Ocean circulation suggests that phytoplankton are circulating to progressively deeper ocean layers with less UV irradiation. Human health is also modified by climate change and behaviour patterns, resulting in changes in exposure to UV-radiation with harmful or beneficial effects depending on conditions and skin type. For example, incidence of melanoma has been associated with increased air temperature, which affects time spent outdoors and thus exposure to UV-radiation. Overall, implementation of the Montreal Protocol and its Amendments has mitigated the deleterious effects of high levels of UV-radiation and global warming for both environmental and human health.

Climate change driven ocean warming is a worldwide environmental issue that can impact cycling of greenhouse gases. However, how methane production in marine sediments as a potential contributor to atmospheric greenhouse gases versus its consumption at the sulfate–methane transition zone will be affected by climate change related warming is still not well constrained. In this study, sediments from two Baltic Sea bays with long-term temperature differences were collected during summer and winter. The primary difference between the two bays was that one had been heated by a nearby power plant for 50 years, resulting in a 5.1 °C increase in annual average temperature compared to an unheated control bay. The results showed that near-seafloor sediment methane concentrations were 50 times higher compared to present-day conditions. Furthermore, the sediment fluxes along with microbial community composition changes suggested that long-term warming may thin the sulfate reduction zone, such that methanotrophic archaea and sulfate reducing bacteria peaked at shallower sediment depths in the heated bay. Overall, the results from long-term warming in natural sediment environment indicated that future climate change warming may increase the risk of methane release to the water and eventually the atmosphere.

The lack of a fitness-based theory of micronutrient allocation to specific tissues hinders understanding of the ultimate causes of mass juvenile mortality due to thiamine (vitamin B1) deficiency, which is an emerging threat to marine and coastal ecosystems worldwide. We modeled the optimal allocation of thiamine in salmon to somatic and reproductive tissues to investigate correlations between tissue thiamine levels, adult mortality, juvenile recruitment, and excretion rates that change with thiamine concentration. The model showed a positive correlation between thiamine levels in gonads and muscles, with a slope that increased with time. This was driven by a constrained thiamine input in salmon, but a negative or no correlation was found in scenarios with high thiamine input. These predictions were confirmed by analysis of empirical data from Atlantic salmon (Salmo salar) populations that differ in the occurrence of episodic thiamine deficiency. A positive correlation was indicative of low thiamine input, regardless of how juvenile recruitment and adult survival increased with thiamine concentration. The model output suggests that renal (i.e., kidney) reuptake is fundamental to understanding micronutrient allocation strategies. Measuring correlations between micronutrient concentrations in reproductive and somatic tissues of adults may help to detect early signs of thiamine deficiency before mass mortality of juveniles occurs. This can complement the previously suggested tissue concentrations and food web indicators. Future studies should try to distinguish and quantify the factors that alter the net thiamine input in salmonids and the subsequent allocation to offspring. Particular attention should be given to changes in thiamine uptake from the diet, including intestinal uptake mechanisms and effects of thiaminase activity. Additionally, more information is needed on internal factors that reduce thiamine availability, such as thiamine degradation as an antioxidant during lipid metabolism, and other physiological factors that can potentially increase thiamine loss, including allocation mechanisms and renal processes.

Background: Vitamin B1 (thiamin) is essential to life; yet little is known of the regulation of its availability in marine environments or how it varies seasonally. Since microbes are the key synthesizers of the vitamin in marine environments, we here used metatranscriptomics to examine the seasonal dynamics of B1 acquisition strategies (including both uptake and synthesis pathways) in Baltic Sea bacterioplankton.

Results: Elevated B1-related gene expression was observed in summer, coinciding with increased temperatures and bacterial activity and decreased nutrient availability. Different bacterial taxa exhibited distinct B1 acquisition strategies. We identified filamentous Cyanobacteria of the order Nostocales as critical to sustaining B1 production during summer, potentially compensating for limited synthesis in heterotrophic bacteria, especially for 4-amino-5-hydroxymethylpyrimidine (HMP) synthesis. Also, Pelagibacterales accounted for major portions of the community transcription, primarily taking up and salvaging the B1 precursor HMP during summer. This study highlights the partitioning of B1 synthesis, salvage, and uptake among microbial taxa, underscoring that transcriptional activity was more dynamic over time than changes in the genomic potential.

Conclusions: We emphasize the influence of environmental conditions on microbial community dynamics and B1 cycling in general, and the potential implications of global change-induced increases in filamentous Cyanobacteria blooms on vitamin food web transfer in particular.

Organisms in systems with seasonality require adaptations that enable them to endure harsh conditions and to emerge again at an optimal time to start a new period of production. One such adaptation is dormant eggs in zooplankton. While there is much information on the cues leading to the production of dormant eggs, less is known about the termination and hatching of these eggs, especially among marine zooplankton. Our results from a combined laboratory and field study at a coastal Baltic Sea site showed that hatching in some overwintering copepods was temperature-dependent, with a threshold-like initiation between 6 degrees C and 9 degrees C. In contrast, overwintering rotifers hatched in comparable abundances in all temperatures, once a similar amount of degree-days had been accumulated. The field study demonstrated that nauplii started to appear when temperatures increased above 6.8 degrees C and were more abundant close to the sediment than in surface water in early spring, matching the hatching threshold found in the laboratory. Various rotifers increased in abundance at different times during the spring phenology, but without any differences in abundance between deep and surface waters. Hence, the hatching of zooplankton dormant eggs in this system is temperature-dependent, likely taxa-specific, and continued climate change is predicted to have implications for the plankton phenology, mismatches, and food web composition.

Human activities increase turbidity in aquatic environments worldwide, which often affects fish behaviour. However, predicting how species react to higher turbidity remains difficult, as responses vary depending on the species, their ecology and the ecosystem. It is thus important to improve our understanding of the responses of fishes living in ecosystems experiencing recent increases in turbidity, especially those with unique species compositions where biodiversity is most vulnerable. One such ecosystem is Lake Tanganyika in East Africa, which is home to a diverse fish community with a high degree of endemism. In this study, we conducted a laboratory experiment with the territorial cichlid, Neolamprologus pulcher, which is endemic to Lake Tanganyika, to investigate the effects of increased turbidity on territorial and exploratory behaviour. We found that moderate increases in turbidity led to reduced territory defence, decreased exploration and increased time spent in shelters. Given that these fish live in large colonies, feed on planktonic particles in the water column and defend their territory against conspecific and heterospecific intruders, these behavioural changes are likely to have substantial implications for their social structure and reproduction in their native environments. Our study raises important questions about whether these effects will persist in the long term as human activities are likely to continue to increase turbidity in the lake over the coming decades and whether the responses to turbidity affect the community composition of fishes in Lake Tanganyika.

Constructed wetlands and constructed floating wetlands are widely used for nitrogen (N) removal from surface water to combat eutrophication in freshwaters. Two main N removal pathways in freshwaters are plant biomass N uptake and denitrification, i.e. transformation of nitrate (NO3-) to nitrous oxide (N2O) or nitrogen gas (N2) by different microbes possessing nirK, nirS, nosZI, and nosZII genes. In this study, we tested woodchips-based floating beds (WFBs) as a nature-based and environment-friendly method to remove nitrate-nitrogen (NO3-N) from water. Moreover, we tested whether WFBs could support the growth of three selected plant species and the abundance of microbes on plant roots and woodchips as a proxy for WFBs' denitrification potential. We conducted a greenhouse experiment for 90 days and measured NO3-N removal rates from water in WFBs mesocosms during five sampling occasions. Plant biomass production, biomass N uptake, and plant morphology related to N uptake and abundance of denitrifying organisms were measured at the end of the experiment. NO3-N removal rates were 29.17 +/- 11.07, 28.18 +/- 12.62, 25.28 +/- 9.90, and 22.16 +/- 7.79 mg L-1 d-1 m-2 (mean +/- standard deviation) in Glyceria maxima, Juncus effusus, Filipendula ulmaria, and unplanted WFBs treatments, respectively for whole experimental period. N content in above- and belowground biomass of studied species ranged between 0.98 - 1.15 and 1.09 - 1.28 (% dry weight), respectively. Plant relative biomass production was 215 +/- 61, 67 +/- 18, and 7 +/- 17 (% dry weight) for G. maxima, J. effusus and F. ulmaria, respectively. Denitrifiers were detected both on plant roots and woodchips, indicating WFBs' denitrification potential. Our study highlights that WFBs could be applied to enhance NO3-N removal from surface water through plant biomass uptake and denitrification processes. Future studies should consider the long-term in situ application of WFBs for NO3-N removal from water.

Climate change related warming is a serious environmental problem attributed to anthropogenic activities, causing ocean water temperatures to rise in the coastal marine ecosystem since the last century. This particularly affects benthic microbial communities, which are crucial for biogeochemical cycles. While bacterial communities have received considerable scientific attention, the benthic eukaryotic community response to climate change remains relatively overlooked. In this study, sediments were sampled from a heated (average 5°C increase over the whole year for over 50 years) and a control (contemporary conditions) Baltic Sea bay during four different seasons across a year. RNA transcript counts were then used to investigate eukaryotic community changes under long-term warming. The composition of active species in the heated and control bay sediment eukaryotic communities differed, which was mainly attributed to salinity and temperature. The family level RNA transcript alpha diversity in the heated bay was higher during May but lower in November, compared with the control bay, suggesting altered seasonal activity patterns and dynamics. In addition, structures of the active eukaryotic communities varied between the two bays during the same season. Hence, this study revealed that long-term warming can change seasonality in eukaryotic diversity patterns. Relative abundances and transcript expression comparisons between bays suggested that some taxa that now have lower mRNA transcripts numbers could be favored by future warming. Furthermore, long-term warming can lead to a more active metabolism in these communities throughout the year, such as higher transcript numbers associated with diatom energy production and protein synthesis in the heated bay during winter. In all, these data can help predict how future global warming will affect the ecology and metabolism of eukaryotic community in coastal sediments.