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Deep-sea food-web structure at South Sandwich Islands (Southern Ocean): net primary production as a main driver for interannual changes
Full text linkFood-webs are a major component of ecosystems and determinant for their functioning and structure. The food chain length (FCL) is a key feature of food-webs and it is crucial for the resistance of the community to external stressors. The Southern Ocean (SO) food-web is known for being short and dominated by an Antarctic krill Euphausia superba surplus, though recent studies proved the existence of different pathways. However, previous studies focused on the pelagic realm, with the deep-sea and benthopelagic coupling remaining poorly understood. Using stable isotopes of δ13C and δ15N in muscle from individuals collected during toothfish fishing seasons 2020, 2021 and 2022, we 1) studied the bathyal food-web structure at South Sandwich Islands; 2) evaluated the interannual variability of FCL; and 3) tested which FCL hypothesis better explains the variability at the SO deep-sea. Our results show that this food-web is composed of five trophic levels with both Patagonian Dissostichus eleginoides and Antarctic Dissostichus mawsoni toothfish as top predators. The 4th and 5th trophic levels are mostly composed of fish, while in the 3rd trophic level we mainly found cephalopods and crustaceans. The benthopelagic coupling occurs at different trophic levels, though mostly between the 3rd and 4th trophic level. The FCL varied between years, being in 2022 0.30 trophic levels shorter than in 2020. Our results suggest that food-webs including a benthic component are longer than pelagic and coastal SO food-webs. The FCL is positively related with net primary productivity, supporting that the productivity hypothesis explains the variability in FCL in SO bathyal food-webs in slope and seamount areas. With climate change, the productivity in the SO is expected to increase which will increase the length of the food-web. This change will affect the structure of the ecosystem, increasing assimilation losses, exposure to biomagnifying contaminants and changing nutrient cycles
Flexible or fortified? How lichens balance defence strategies across climatic harshness gradients
Full text linkLichens play important roles in habitat formation and community succession in polar and alpine ecosystems. Despite their significance, the ecological effects of lichen traits remain poorly researched. We propose a trait trade-off for managing light exposure based on climatic harshness. In the harshest cold environments, where abiotic stress predominates over biotic pressures, lichens should rely on photostable, recalcitrant and immobile substances such as allomelanin and hydrophobic compounds. These compounds provide durable protection without the need for continual synthesis. In milder conditions where biotic interactions – e.g. competition and pathogen presence – become increasingly pronounced, lichens should retain flexibility and produce simple protective secondary compounds that, in addition to functioning as light screens, can leach out to influence their direct environment. Preliminary empirical findings for Antarctic lichen species distribution are consistent with this hypothesised trade-off, in that lichens producing soluble compounds dominate in milder regions and are less represented at higher southern latitudes, where species producing insoluble compounds with a melanised thallus dominate. As climate change progresses, increasing temperatures and precipitation could make the currently coldest and driest areas more hospitable, allowing the ranges of lichens producing soluble compounds to expand, with cascading effects on rock weathering, nutrient cycling and other ecosystem processes
TIMED Doppler Interferometer measurements of neutral winds at the mesosphere and lower thermosphere and comparison to meteor radar winds
Full text linkThe mesosphere and lower thermosphere (MLT) comprise a highly variable region that forms the transition region between the middle and upper atmosphere. The variability of this region is driven by atmospheric waves transporting energy and momentum from the lower and middle atmosphere to MLT altitudes. These waves cover a wide range of temporal (minutes to days) and spatial (kilometers to planetary) scales. The upward propagation of atmospheric gravity waves and tides is one of the key processes at all latitudes that alters the state of the ionosphere–thermosphere system, and their vertical propagation depends crucially on the background mean winds. The TIMED Doppler Interferometer (TIDI) on board the Thermosphere-Ionosphere-Mesosphere-Energetics and Dynamics (TIMED) satellite observes neutral winds at the MLT using airglow emissions. We establish a TIDI mean wind climatology, compare our results with existing climatologies derived from local meteor radar observations, and discuss similarities and differences depending on local time and geographical latitude
Using zebrafish G protein-coupled receptors to obtain a better appreciation of the impact of pharmaceuticals in wastewater to fish
No full textPharmaceutical discharge to the environment is of concern due to its potential adverse effects on aquatic species. It is estimated that around 40% of pharmaceuticals target G protein-coupled receptors (GPCRs). The in vitro transforming growth factor-α (TGFα) shedding assay was applied to measure the antagonistic activities of pharmaceuticals against human GPCRs. However, their ability to stimulate fish GPCRs remains unclear. Here, antagonistic activities of 30 pharmaceuticals against zebrafish dopamine (zD2a and zD2c), adrenergic family member (zβ1), and histamine (zH1 and zH3) receptors were measured by the TGFα shedding assay. The study found an interspecies difference in binding affinities between human and zebrafish: pharmaceuticals more strongly inhibited the zD2c and zH1 receptors than human D2 (hD2) and hH1 receptors, while zD2a and zβ1 receptors were less inhibited than hD2 and hβ1 receptors. The potential molecular explanations for the observed interspecies differences in binding affinity for hydroxyzine and bisoprolol were investigated using molecular docking. Pharmaceutical potency against zebrafish GPCRs and predicted effluent concentrations were used to predict equivalent quantities (EQs), and these EQs were used to prioritize pharmaceuticals of concern in wastewater in England and Japan. This study highlights the use of the TGFα shedding assay adopting zebrafish GPCRs to better understand the ecological effects of pharmaceuticals on fish
Tropical forest clearance impacts biodiversity and function, whereas logging changes structure
Full text linkThe impacts of degradation and deforestation on tropical forests are poorly understood, particularly at landscape scales. We present an extensive ecosystem analysis of the impacts of logging and conversion of tropical forest to oil palm from a large-scale study in Borneo, synthesizing responses from 82 variables categorized into four ecological levels spanning a broad suite of ecosystem properties: (i) structure and environment, (ii) species traits, (iii) biodiversity, and (iv) ecosystem functions. Responses were highly heterogeneous and often complex and nonlinear. Variables that were directly impacted by the physical process of timber extraction, such as soil structure, were sensitive to even moderate amounts of logging, whereas measures of biodiversity and ecosystem functioning were generally resilient to logging but more affected by conversion to oil palm plantation
A first look at xenophyophores (Rhizaria, Foraminifera) in the lower bathyal Bering Sea and abyssal areas adjacent to the Aleutian Trench
Full text linkXenophyophores are an abundant component of the megafauna in parts of the equatorial and temperate North Pacific, but few records exist of these giant agglutinated foraminifera in northern North Pacific and adjacent waters. Here, we present a preliminary survey of xenophyophores from the bathyal Bering Sea (∼3500 m depth) and at abyssal depths (4294–6555 m) adjacent to the Aleutian Trench, based on collected material, mainly fragments, and seafloor images. The dominant xenophyophore in the Bering Sea is a reticulated form that yielded DNA sequences identical to those obtained from Syringammina limosa, a species described from > 2700 km to the west in the Sea of Okhotsk. Also visible in seafloor photographs were various plate-like forms, often with upturned, undulating rims, but also branching plates and other more complicated morphotypes that probably represent distinct species. At stations close to the Aleutian Trench, core and epibenthic sledge samples yielded xenophyophores at seven of the 16 sampling sites. At least eleven morphospecies were recognised among those collected, none resembling S. limosa or the plate-like Bering Sea forms. Seafloor images revealed 16 fairly distinct domed or plate-like morphotypes three of these are possibly represented among the collected specimens, making a total of around 24 morphotypes or morphospecies. A few images show morphotypes similar to those seen in the Bering Sea. Our results suggests that xenophyophores are as diverse in the northern North Pacific as they are elsewhere in the Pacific Ocean
The prevalence of Phytophthora in British plant nurseries; high‐risk hosts and substrates and opportunities to implement best practice
Full text linkInvasive Phytophthora species infect a very broad range of herbaceous and woody hosts globally. The UK alone has experienced a particularly damaging series of outbreaks and epidemics of new, invasive Phytophthora species affecting the nation's trees over the last 30 years. The link between Phytophthora outbreaks and the importation and spread of infected nursery stock is well established across many countries worldwide. To understand better the pathways of spread of Phytophthora in the nursery trade in Britain, we applied a standardized nursery sampling method combined with a refined metabarcoding detection method to capture the diversity of Phytophthora species at 134 British plant nurseries representing a range of biosecurity and trading practices over multiple sampling years between 2016 and 2022. This included root and water samples collected from 17 nurseries sampled seasonally and root samples collected from 117 nurseries sampled once as part of plant health inspections. Based on analyses of 1894 pooled samples, DNA barcodes of 85 Phytophthora species or complexes were detected, with variation in species' relative frequencies across nurseries. We present the top 20 host– Phytophthora associations ranked by relative frequency and report five novel Phytophthora records for the UK. We identified surprisingly high‐risk hosts (such as Douglas fir) with the greatest number of Phytophthora associations and revealed Phytophthora nursery niche preferences for water or roots. We discuss the implications of our findings in terms of pathogen diversity and abundance, high‐risk hosts, our information dissemination approach and resulting advice on nursery practices aimed at reducing risk
Tipping point-induced abrupt shifts in East Asian hydroclimate since the Last Glacial Maximum
Full text linkMultiple tipping points in the Earth system could be triggered when global warming exceeds specific thresholds. However, the degree of their impact on the East Asian hydroclimate remains uncertain due to the lack of quantitative rainfall records. Here we present an ensemble reconstruction of East Asian summer monsoon (EASM) rainfall since the Last Glacial Maximum (LGM) using nine statistical and machine learning methods based on multi-proxy records from a maar lake in southern China. Our results define five tipping points in the EASM rainfall since the LGM, which are characterized by abrupt and irreversible regime shifts with a median amplitude of 387 ± 73 mm (24 ± 5 %). Combined with multi-model simulations and existing records, we attribute these tipping points to cascades of abrupt shifts in the Atlantic meridional overturning circulation (AMOC) and Saharan vegetation. Our findings underscore the nonlinear behavior of the EASM and its coupling with other tipping elements
The Ronne Ice Shelf survived the last interglacial
Full text linkThe fate of the West Antarctic Ice Sheet (WAIS) is the largest cause of uncertainty in long-term sea-level projections. In the last interglacial (LIG) around 125,000 years ago, data suggest that sea level was several metres higher than today, and required a significant contribution from Antarctic ice loss, with WAIS usually implicated. Antarctica and the Southern Ocean were warmer than today, by amounts comparable to those expected by 2100 under moderate to high future warming scenarios. However, direct evidence about the size of WAIS in the LIG is sparse. Here we use sea salt data from an ice core from Skytrain Ice Rise, adjacent to WAIS, to show that, during most of the LIG, the Ronne Ice Shelf was still in place, and close to its current extent. Water isotope data are consistent with a retreat of WAIS, but seem inconsistent with more dramatic model realizations in which both WAIS and the large Antarctic ice shelves were lost. This new constraint calls for a reappraisal of other elements of the LIG sea-level budget. It also weakens the observational basis that motivated model simulations projecting the highest end of projections for future rates of sea-level rise to 2300 and beyond
The Pleistocene Witch Ground Ice Stream in the central North Sea
Full text linkThe North Sea Basin has been covered by ice sheets originating from both the British Isles and Scandinavia at multiple times during the Pleistocene. The Witch Ground Basin (WGB) in the central northern North Sea is a critical location in terms of interpreting Late Pleistocene glacial to glacimarine history of the North Sea since it was the location of the Witch Ground Ice Stream that was active on multiple occasions during the Mid to Late Pleistocene. We map five mega‐scale glacial lineation flowsets corresponding to the changing ice flow direction of the Witch Ground Ice Stream and investigate the sedimentological fingerprint and corresponding subglacial depositional processes of this palaeo‐ice stream. We show that sorted sand layers within a subglacial traction till represent periodic hydraulic jacking and ice–bed decoupling at the base of the Witch Ground Ice Stream. In contrast to previous studies that have described glacitectonites deposited below the most recent grounded ice in the WGB, we present analysis of sediment cores that recovered primarily massive diamictons without any obvious deformation structures. The most recent ice cover in the WGB (~18–16 ka) was thought to have been sourced from a localized ice cap over Orkney and Shetland. The presence of chalk clasts sourced from NW of the WGB described in this study from the stratigraphically youngest till confirms this interpretation. The transition from subglacial to glacimarine deposition, while acoustically well defined (from opaque to laminated acoustic units), appears surprisingly uniform in the recovered sediment cores, but can be differentiated based on a change in colour including mottling and banding, presence of whole intact shells, and the increased number of silt and sand lenses. 14 C dating of glacimarine muds indicate high sedimentation rates of between 80 and 260 cm ka −1 . The transition from glacimarine to marine deposition is represented by a comparative decrease in sedimentation rate and deposition of Holocene age sandy mud. This study demonstrates a highly dynamic Witch Ground Ice Stream in the northern North Sea during the Late Pleistocene with evolving subglacial hydrology and depositional processes at the ice stream bed that left a distinct geomorphological and sedimentological fingerprint within the WGB
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