Seasonal Dietary Shifts of the Gammarid Amphipod Gondogeneia antarctica in a Rapidly Warming Fjord of the West Antarctic Peninsula

The amphipod Gondogeneia antarctica is among the most abundant benthic organisms, and a key food web species along the rapidly warming West Antarctic Peninsula (WAP). However, little is known about its trophic strategy for dealing with the extreme seasonality of Antarctic marine primary production. This study, using trophic markers, for the first time investigated seasonal dietary shifts of G. antarctica in a WAP fjord. We analyzed δ13C and δ15N in G. antarctica and its potential food sources. The isotopic signatures revealed a substantial contribution of red algae to the amphipod diet and also indicated a significant contribution of benthic diatoms. The isotope results were further supported by fatty acid (FA) analysis, which showed high similarities in FA composition (64% spring–summer, 58% fall–winter) between G. antarctica and the red algal species. G. antarctica δ13C showed a small shift seasonally (−18.9 to −21.4‰), suggesting that the main diets do not change much year-round. However, the relatively high δ15N values as for primary consumers indicated additional dietary sources such as animal parts. Interestingly, G. antarctica and its potential food sources were significantly enriched with δ15N during the fall–winter season, presumably through a degradation process, suggesting that G. antarctica consumes a substantial portion of its diets in the form of detritus. Overall, the results revealed that G. antarctica relies primarily on food sources derived from benthic primary producers throughout much of the year. Thus, G. antarctica is unlikely very affected by seasonal Antarctic primary production, and this strategy seems to have allowed them to adapt to shallow Antarctic nearshore waters.

Linking extreme seasonality and gene expression in arctic marine protists

At high latitudes, strong seasonal differences in light availability affect marine organisms and restrict the timing of ecosystem processes. Marine protists are key players in Arctic aquatic ecosystems, yet little is known about their ecological roles over yearly cycles. This is especially true for the dark polar night period, which up until recently was assumed to be devoid of biological activity. A 12 million transcripts catalogue was built from 0.45-10 μm protist assemblages sampled over 13 months in a time series station in an arctic fjord in Svalbard. Community gene expression was correlated with seasonality, with light as the main driving factor. Transcript diversity and evenness were higher during polar night compared to polar day. Light-dependent functions had higher relative expression during polar day, except phototransduction. 64% of the most expressed genes could not be functionally annotated, yet up to 78% were identified in arctic samples from Tara Oceans, suggesting that arctic marine assemblages are distinct from those from other oceans. Our study increases understanding of the links between extreme seasonality and biological processes in pico- and nanoplanktonic protists. Our results set the ground for future monitoring studies investigating the seasonal impact of climate change on the communities of microbial eukaryotes in the High Arctic.

Early Jurassic phytotoxicity due to Hg-remobilization

<p>The Central Atlantic Magmatic Province (CAMP) eruptions are generally regarded as the main driver of major environmental change and mass-extinction across the Triassic-Jurassic (TJ) boundary (~201.3 Ma), but the exact mechanisms linking volcanism and extinction, resilience, and recovery remain poorly constrained. Volcanogenic mercury (Hg) has been implicated as the cause for mutations in spores/pollen indicating severe ecological stress in terrestrial vegetation. Indeed, elevated sedimentary Hg concentrations coincide with the extinction interval at multiple sites across Europe. Here we show, palynological and geochemical records that gives insight in the dynamics between the Hg cycle and terrestrial vegetation, indicating repeated phytotoxicity in Early Jurassic deposits.</p><p>The abundance of mutagenic spores and the concentration of Hg are quantified in shallow marine sediments in the Schandelah-1 core (northern Germany) across the T/J boundary and the Early Jurassic (Hettangian). The results show increased mutagenic spore abundances with accompanying Hg/TOC anomalies across the end-Triassic extinction and within the lowermost Hettangian. This is consistent with studies from Sweden and Denmark and therefore confirming synchronous mutagenesis in and around coastal European margins. In addition, the Hettangian of Schandelah contains a record of long-term vegetational disturbance in the form of recurrent fern spikes and elevated mutagenic spore intervals, accompanied by Hg/TOC anomalies of similar magnitude. This suggests an overall link between volcanogenic pollution and vegetational disturbance. Based on qualitative analyses of organic matter (OM), which show an overall positive correlation between Hg concentration and terrestrial indicators, alternative sources for sedimentary Hg-enrichment such as vegetation reservoirs should be considered. This characterization of OM indicates an intermediate step in the Hg cycle, likely mediated by vegetation and/or climate feedbacks.</p><p>Atmospheric Hg-loading via volcanism can explain the synchronous enrichments of Hg concentrations at the TJ boundary interval in multiple sites across the globe. In contrast, the Hettangian anomalies of Schandelah-1, appear to be mainly driven by environmental/ecological perturbations corresponding to intensifying warm/humid conditions. Extreme seasonality alternating between high rainfall and droughts, perhaps due to eccentricity maxima, leading to increased soil erosion, wildfires and transport/degradation of terrestrial OM could potentially recycle and redistribute Hg long after initial deposition. These implications suggest a more dominant role of climate-induced Hg-remobilization, rather than direct volcanic emissions, to the mutagenesis in terrestrial vegetation. This could, in addition, lead to asynchronous and local impacts mainly in the proximity of landmasses.</p>

Comparison of Two 16S rRNA Primers (V3–V4 and V4–V5) for Studies of Arctic Microbial Communities

Microbial communities of the Arctic Ocean are poorly characterized in comparison to other aquatic environments as to their horizontal, vertical, and temporal turnover. Yet, recent studies showed that the Arctic marine ecosystem harbors unique microbial community members that are adapted to harsh environmental conditions, such as near-freezing temperatures and extreme seasonality. The gene for the small ribosomal subunit (16S rRNA) is commonly used to study the taxonomic composition of microbial communities in their natural environment. Several primer sets for this marker gene have been extensively tested across various sample sets, but these typically originated from low-latitude environments. An explicit evaluation of primer-set performances in representing the microbial communities of the Arctic Ocean is currently lacking. To select a suitable primer set for studying microbiomes of various Arctic marine habitats (sea ice, surface water, marine snow, deep ocean basin, and deep-sea sediment), we have conducted a performance comparison between two widely used primer sets, targeting different hypervariable regions of the 16S rRNA gene (V3–V4 and V4–V5). We observed that both primer sets were highly similar in representing the total microbial community composition down to genus rank, which was also confirmed independently by subgroup-specific catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH) counts. Each primer set revealed higher internal diversity within certain bacterial taxonomic groups (e.g., the class Bacteroidia by V3–V4, and the phylum Planctomycetes by V4–V5). However, the V4–V5 primer set provides concurrent coverage of the archaeal domain, a relevant component comprising 10–20% of the community in Arctic deep waters and the sediment. Although both primer sets perform similarly, we suggest the use of the V4–V5 primer set for the integration of both bacterial and archaeal community dynamics in the Arctic marine environment.

The Genomic Capabilities of Microbial Communities Track Seasonal Variation in Environmental Conditions of Arctic Lagoons

In contrast to temperate systems, Arctic lagoons that span the Alaska Beaufort Sea coast face extreme seasonality. Nine months of ice cover up to ∼1.7 m thick is followed by a spring thaw that introduces an enormous pulse of freshwater, nutrients, and organic matter into these lagoons over a relatively brief 2–3 week period. Prokaryotic communities link these subsidies to lagoon food webs through nutrient uptake, heterotrophic production, and other biogeochemical processes, but little is known about how the genomic capabilities of these communities respond to seasonal variability. Replicate water samples from two lagoons and one coastal site near Kaktovik, AK were collected in April (full ice cover), June (ice break up), and August (open water) to represent winter, spring, and summer, respectively. Samples were size fractionated to distinguish free-living and particle-attached microbial communities. Multivariate analysis of metagenomes indicated that seasonal variability in gene abundances was greater than variability between size fractions and sites, and that June differed significantly from the other months. Spring (June) gene abundances reflected the high input of watershed-sourced nutrients and organic matter via spring thaw, featuring indicator genes for denitrification possibly linked to greater organic carbon availability, and genes for processing phytoplankton-derived organic matter associated with spring blooms. Summer featured fewer indicator genes, but had increased abundances of anoxygenic photosynthesis genes, possibly associated with elevated light availability. Winter (April) gene abundances suggested low energy inputs and autotrophic bacterial metabolism, featuring indicator genes for chemoautotrophic carbon fixation, methane metabolism, and nitrification. Winter indicator genes for nitrification belonged to Thaumarchaeota and Nitrosomonadales, suggesting these organisms play an important role in oxidizing ammonium during the under-ice period. This study shows that high latitude estuarine microbial assemblages shift metabolic capabilities as they change phylogenetic composition between these extreme seasons, providing evidence that these communities may be resilient to large hydrological events in a rapidly changing Arctic.

A marine zooplankton community vertically structured by light across diel to interannual timescales

The predation risk of many aquatic taxa is dominated by visually searching predators, commonly a function of ambient light. Several studies propose that changes in visual predation will become a major climate-change impact on polar marine ecosystems. The High Arctic experiences extreme seasonality in the light environment, from 24 h light to 24 h darkness, and therefore provides a natural laboratory for studying light and predation risk over diel to seasonal timescales. Here, we show that zooplankton (observed using acoustics) in an Arctic fjord position themselves vertically in relation to light. A single isolume (depth-varying line of constant light intensity, the value of which is set at the lower limit of photobehaviour reponses of Calanus spp. and krill) forms a ceiling on zooplankton distribution. The vertical distribution is structured by light across timescales, from the deepening of zooplankton populations at midday as the sun rises in spring, to the depth to which zooplankton ascend to feed during diel vertical migration. These results suggest that zooplankton might already follow a foraging strategy that will keep visual predation risk roughly constant under changing light conditions, such as those caused by the reduction of sea ice, but likely with energetic costs such as lost feeding opportunities as a result of altered habitat use.

The Anaconda Challenge

This chapter focuses on the llanos, Venezuela’s natural floodplain, where the author decided to start his study of anacondas. The llanos is a flatland that comprises about a third of both Venezuela and Colombia. It is composed of an extensive system of natural, seasonally flooded grasslands. The llanos is located to the north and west of the Orinoco River and sits on the northern borders of the Amazon basin. Because of this, most of the wildlife of the Amazon can be found in the llanos, where it is easier to observe animals in the open vegetation of the savanna. The extreme seasonality of the llanos made all the difference in the success of the author’s anaconda research. Anacondas, being aquatic, concentrate in the few water bodies that hold water during the dry season. During this time, the chance of finding anacondas was much higher. The chapter then explores the physical build of snakes. Most snakes have adaptations of the skull and jaws involving mobile hinges, and a whole arrangement of joints and muscles evolved for swallowing large prey. The extra mobility of the snake’s jaws is obtained by giving up solid skull sutures that the ancestral lizards had, rendering the snake’s head more vulnerable to damage.

Changing winter conditions in the Alps during the Younger Dryas cold period

<p>The Younger Dryas (YD, GS-1) is the latest of the canonical millennial-scale stadials of the last glacial period. Proxy data from terrestrial archives point to a climate dominated by extreme seasonality and continentality across Europe. YD summers were characterised by large meridional temperature gradients and remained quite warm despite the prominent slowdown of the Atlantic Meridional Overturning Circulation. The few available winter proxy records point to cold and dry winters.</p><p>In the Alps, the YD was characterised by the last major glacier advance and the development of rock glaciers. Dating these cryogenic geomorphological features, however, is associated with substantial uncertainties. A new type of secondary carbonate archive (coarsely crystalline cryogenic cave carbonates, or CCC<sub>coarse</sub>) has received increasing attention as a promising quantitative cryogenic indicator for the shallow subsurface environment. CCC<sub>coarse</sub> are found in karst caves and their formation is directly linked to thawing of perennial cave ice and U-series disequilibrium methods allow to date these events at high precision.</p><p>CCC<sub>coarse</sub> formed during the YD were found in three caves covering an approximately 170 km-long SW-NE transect. The entrance of Cioccherloch cave is located at 2245 m in the Dolomites; Frauenofen opens in the Tennengebirge at 1635 m, while the third cave, Großes Almbergloch, is situated in Totes Gebirge at an elevation of 1475 m. The thermal regime in Cioccherloch reflects the ambient mean annual air temperature, while the cave microclimate of Frauenofen and Großes Almbergloch is partially influenced by cold air intrusions in winter.</p><p><sup>230</sup>Th dating of twenty-two CCC<sub>coarse</sub> samples demonstrates that perennial ice was present in these caves during the first part of the YD, and Großes Almbergloch, Cioccherloch and Frauenofen warmed to 0°C at 12.32 ±0.09, 12.20 ±0.09, and 12.01 ±0.04 ka BP (weighted means), respectively, initiating slow thawing of cave ice bodies. Due to the partial cold trap behaviour of Frauenofen and Großes Almbergloch, a delay in cave ice demise and thus CCC<sub>coarse </sub>formation is likely. This and the higher elevation could explain the centennial lag observed in CCC<sub>coarse </sub>deposition in Frauenofen compared to Großes Almbergloch.</p><p>The change in the thermal condition of these caves commencing at ~12.3 ±0.1 ka BP is attributed to a change in the winter climate in the Alps, from dry to snow-rich and/or from extremely cold to milder winters. A snowpack could effectively insulate the shallow subsurface from the YD winter coldness, allowing the subsurface to slowly warm. The timing of this warming of the subsurface coincides with the mid-YD transition recorded in other archives across Europe (e.g., Meerfelder Maar, central Germany; El Soplao cave, northern Spain) and corroborates the hypothesis of a northward movement of the Westerlies during the mid-YD, bringing warmer air and moisture to the Alps. Our study also demonstrates that the interpretation of CCC<sub>coarse</sub> data requires a sound understanding of the cave geometry and the resulting mode of air exchange, since both the onset of perennial ice build-up and the eventual thawing may lag the atmospheric forcing outside the cave.</p>

Remote sensing-aid assessment of wetlands in central Malawi

<p>Many areas in Malawi undergo extreme seasonality: floods in the wet season and drought in the dry season. Each year, this extreme seasonality poses formidable challenges for local farmers to sustain their crops. Often in the dry season, farmers use the water in the surrounding seasonal wetlands (dambos) for small-scale irrigation to supplement their rainy season harvest. In Malawi, the agricultural use of wetland is growing year by year and these areas play significant roles in regulating food price shocks and price. Such intensive use of wetlands can negatively affect the sustainability of wetland eco-system and their crop production, with communities even affected by the drying up of wells. Farmers, especially small-scale farmers, will face even more challenges for sustaining wetland production, as climate changes cause more frequent occurrence of droughts as Malawi has experienced in recent years. With the increasingly intensive use of these seasonal wetlands for agricultural purpose and the expansion of wetland degradation generally across the country, more attention is required toward effective management of these wetlands through identification, mapping, monitoring and data analysis. To achieve the sustainable use of these seasonal wetlands, it is essential to establish systematic monitoring and assessment procedures. Widely used assessment protocols (i.e., WET-Health) which evaluate the wetlands based on physical indicators such as land cover, hydrology, geomorphology, soil organic matter and natural vegetation have been successfully implemented in South Africa. However, obtaining those indicators across the full length of an individual wetland, let alone all wetlands in one district in Malawi, is labour intensive and time-consuming and difficult to complete. In this research, we utilise both unmanned aerial vehicle (UAV) and satellite imageries. These data sources are being tested in nine different seasonal wetlands in central Malawi to provide an accurate derivation of key indicators such as gully formation, sedimentation, water extent, changes in land use and natural vegetation. Additionally, using satellite imageries and GIS, the condition of each individual wetland has been quantified, with land cover and the extent of inundation determined through multi-temporal data analysis. Our results can be applied across a larger area, i.e. several districts to help identify where more detailed ground assessment is needed and technical support required to improve wetland management, feeding into both policy and technical guidance which can help sustain the range of ecosystems services of these important areas.</p>