Distinct Assemblages Research Articles

Late Tithonian (Late Jurassic) palynological record from the Jaisalmer Basin (India)

ABSTRACT Late Tithonian (Late Jurassic) palaeobotanical records from the Jaisalmer Basin are infrequent. We report the first record of an age-diagnostic palynological assemblage of the sedimentary rocks in the Bhadasar Formation from the Jaisalmer Basin, India. The study is carried out to consider the palaeoenvironmental settings in this basin based on palynological and palynofacies investigations. A well-preserved assemblage of palynomorphs with 22 species belonging to 10 genera, including spores and pollen. The palynological assemblage is characterised by the dominance of coniferous pollen of Callialasporites spp. Araucariacites spp. along with some significant taxa viz. Cupressacites ramachandra, Microcachryidites antarcticus, Classopollis sp. Podocarpidites sp. Pityosporites sp. Ginkgoretectina spp. and Monosulcites sp. which suggest a Late Tithonian (Late Jurassic) age. The occurrence of conifer pollens (Araucariacites and Callialasporites) represents coastal vegetation and warm climate. However, some bisaccate pollen (Podocarpidites) indicates drier upland areas. Palynofacies records suggest two distinct Palynofacies Assemblages (PA – I and PA – II) correspond to the marginal oxic to dysoxic basin and the shelf to marginal transition.

Contact metamorphism and dolomitization overprint on Cambrian carbonates from the Ossa-Morena Zone (SW Iberian Massif): implications to Sr-chronology of carbonate rocks

AbstractThe Cambrian Series 2 Carbonate Formation from the Alter do Chão Elvas-Cumbres Mayores unit (Ossa-Morena Zone, SW Iberian Massif) is composed of regionally metamorphosed marbles and marlstones that underwent chlorite zone metamorphism and preserve the primaeval limestone 87Sr/86Sr ratios (0.7083–0.7088). These are consistent with the established Lower Cambrian seawater curve, and therefore used for age constraints in formations lacking fossil contents. The regional mineralogical and Sr-isotopic features of the carbonate rocks are frequently overprinted by the effects of contact metamorphism induced by magmatic bodies emplaced during rift-related and synorogenic events of the Palaeozoic, as well as by post-metamorphic dolomitization processes. The development of calc-silicate minerals due to contact metamorphism is common in the rocks of the Carbonate Formation and apparently results from the interaction of the protolith with fluids of different origin: (i) internally produced fluids released by conductive heating (observed in external contact aureoles) and (ii) external intrusion-expelled fluids that, besides leading to the appearance of distinctive assemblages, also promote an influx of strontium content (observed in roof pendants). Calc-silicate mineralogy varies substantially throughout the region, likely due to the heterogeneous distribution of silicate minerals of the protolith, progression of intrusion-driven fluids, and the irregular effect of thermal gradients. Results suggest that high-grade contact metamorphism (hornblende facies or higher) and dolomitization processes imposed on the Carbonate Formation significantly influence the isotopic signatures of the carbonates, providing limitations in applying Sr-isotopic chronology. Graphical abstract

Tree species selection for optimizing soil carbon storage: Insights from litter decomposition and bacterial community analysis in coastal ecosystems

Coastal wetland ecosystems are critical sinks for atmospheric carbon dioxide, playing a vital role in global carbon cycling and climate regulation. The decomposition of leaf litter plays a crucial role in the formation and stability of soil organic carbon (SOC) in these environments. This study investigated the impact of leaf litter decomposition from five tree species (Populus deltoids, Ligustrum lucidum, Taxodium 'Zhongshanshan', Hibiscus hamabo, and Nerium oleander) on SOC dynamics, humus composition, and soil bacterial community structure in a tidal flat. Litterbags were used to monitor the mass loss and changes in litter chemical composition over 270 days. The results revealed significant differences in decomposition rates among the tree species, with Nerium oleander exhibiting the fastest decomposition and Populus deltoids the slowest. Surprisingly, initial litter chemistry did not correlate with decomposition rates; however, changes in lignin and hemicellulose content during decomposition were significantly related to mass loss. Despite its rapid decomposition, Nerium oleander litter resulted in the highest accumulation of SOC, total humus, and humin compared to the other species, challenging the conventional view that slower decomposition leads to greater SOC storage. The soil microbial community structure was significantly influenced by SOC, humus, and litter components, with distinct microbial assemblages associated with each tree species. A random forest model identified key bacterial taxa, predominantly Proteobacteria, as important predictors of SOC content, highlighting the role of bacterial diversity in regulating SOC dynamics. These findings underscore the importance of considering litter quality, decomposition dynamics, and bacterial community composition in strategies aimed at enhancing soil carbon sequestration. This study suggests that selecting tree species with rapidly decomposing litter, such as Nerium oleander, in coastal plantations can be an effective management tool for optimizing soil carbon storage, offering valuable insights for mitigating climate change impacts.

Understanding an exceptional Afropollis‐dominated flora in the middle Cretaceous palaeotropics of the southern Tethys

AbstractAfropollis is a common element in Cretaceous low‐latitude palynofloras ranging from the Barremian to the Cenomanian. Despite an abundant fossil record, its affinities are still elusive. Nine Afropollis‐rich subsurface samples from the Cenomanian Bahariya Formation in the northern part of the Western Desert of Egypt were palynologically analysed, and the palynoflora was compared with previously published material. The geographical distribution of Afropollis‐yielding strata was compared with known macrofloras. The Bahariya material yielded a distinct palynomorph assemblage dominated by an unusually high frequency of Afropollis jardinus, reaching up to 60.7% of the total palynomorph count. The dominance of A. jardinus may be ecologically related to a near‐coastal lacustrine or lagoonal environment. Its association with two kinds of macrofloras suggests that the plants producing A. jardinus may have been part of a tropical azonal vegetation type, either aquatic or mangrove‐like.

Nephelinites from Burko volcano (Tanzania) record the phase relations among perovskite, magnetite, titanite and andradite in evolved alkaline and silica-undersaturated systems

Nephelinitic rocks from Burko volcano in the Northern Tanzanian Divergence Zone of the East African Rift System represent transitional compositions between primitive and evolved nephelinites which exhibit two distinct phase assemblages, allowing to constrain the magmatic history of such particular rock types. Detailed petrography, mineral compositions and whole rock geochemistry were used to reconstruct the crystallization conditions and the petrological evolution of the Burko rocks and to compare them to the nearby volcanoes of Oldoinyo Lengai and Sadiman. Burko samples report a characteristic mineralogy of intermediate nephelinites (Mg# of 60–40) which comprise nepheline-diopside-magnetite-perovskite assemblages. They evolved mainly via fractionation of clinopyroxene, apatite, magnetite, and perovskite/titanite to peralkaline nephelinites (Mg# of 40–25) comprising nepheline-aegirine-augite-titanite-andradite±K-feldspar assemblages. The presence of unexposed primitive olivine nephelinites is, however, indicated by rare forsterite antecrysts.Reworking of crystal mushes and/or magma mixing are evident from different xenocrysts, antecrysts and pyroxenitic–ijolitic inclusions, precluding simple fractional crystallization modelling. The evolution from diopside-bearing nephelinites towards aegirine-augite-bearing ones was accompanied by a decrease in temperature (from ~1100 to ~900 °C) and an increase of log(aSiO2) towards ~−0.5 and of fO2 (∆FMQ ~2.5 to ~3). Especially in the peralkaline nephelinites, late-stage enrichment of Sr, Ba and halogens is documented by Sr-and F-rich apatite, barytolamprophyllite, celsian, götzenite, and eudialyte. In comparison, evolved and mostly peralkaline nephelinites from the nearby Oldoinyo Lengai and Sadiman volcanoes contain similar mineral assemblages, indicating comparable formation processes, but slightly different melt evolution trajectories. The variations in nephelinite composition and phase assemblages are linked to a) slightly different parental melt compositions related to variable amounts of amphibole, mica and carbonate in the molten mantle veins and b) different crystallization conditions, especially redox conditions, during cooling.

Elevational patterns of bird alpha and beta diversity in Haba Snow Mountain, Southwestern China: Implication for conservation

Understanding environmental patterns of species diversity is essential for nature reserve planning and biodiversity conservation. In this study, we explored the birds’ alpha and beta diversity along the elevational gradients in Haba Snow Mountain Nature Reserve (hereafter, HBSM), a global biodiversity hotspot, and studied which environmental factor is the main driver in explaining alpha and beta diversity patterns. Our results indicated that taxonomic, functional, and phylogenetic alpha diversity consistently exhibited hump-shaped patterns with similar peaks. After controlling for species richness, both functional and phylogenetic alpha diversity increased with elevation, and the peaks at 3400–3700 m. Mean pairwise functional distance remained nearly constant along the elevation band, whereas mean pairwise phylogenetic distance shown hump-shaped pattern, and the predicted MPD peaked at the fifth band (3100–3400 m a.s.l). The functional and phylogenetic structure of bird communities in HBSM were more clustered along the elevation gradients, suggesting environmental filtering likely drove the assembly processes. Additionally, primary productivity (NDVI and/or habitat heterogeneity) and/or precipitation were robust predictors of variation in most diversity metrics. For multiple-site beta diversity, we observed that high turnover component in taxonomic, functional, and phylogenetic dimensions, indicating distinct bird assemblages across various elevational bands. In pairwise beta diversity, the spatial turnover of taxonomic and phylogenetic aspects was higher than nestedness, revealing species replacement occurs relatively frequently between evolutionarily related species with similar niche and functional traits. Overall, our findings highlight the importance of considering both different dimensions and multifaceted diversity when assessing elevational patterns of bird diversity. This study also provides valuable insights into the structuring mechanisms of bird communities and informs conservation planning along elevational gradients in HBSM, and offers a comprehensive case on species richness along elevational gradients.

Metabarcoding reveals ecologically distinct fungal assemblages in river and groundwater along an Austrian alpine to lowland gradient.

Biodiversity, the source of origin, and ecological roles of fungi in groundwater are to this day a largely neglected field in fungal and freshwater ecology. We used DNA-based Illumina high-throughput sequence analysis of both fungal gene markers 5.8S and internal transcribed spacers region 2 (ITS2), improving taxonomic classification. This study focused on the groundwater and river mycobiome along an altitudinal and longitudinal transect of a pre-alpine valley in Austria in two seasons. Using Bayesian network modeling approaches, we identified patterns in fungal community assemblages that were mostly shaped by differences in landscape (climatic, topological, and geological) and environmental conditions. While river fungi were comparatively more diverse, unique fungal assemblages could be recovered from groundwater, including typical aquatic lineages such as Rozellomycota and Olpidiomycota. The most specious assemblages in groundwater were not linked to the input of organic material from the surface, and as such, seem to be sustained by characteristic groundwater conditions. Based on what is known from closely related fungi, our results suggest that the present fungal communities potentially contribute to mineral weathering, carbon cycling, and denitrification in groundwater. Furthermore, we were able to observe the effects of varying land cover due to agricultural practices on fungal biodiversity in groundwater ecosystems. This study contributes to improving our understanding of fungi in the subsurface aquatic biogeosphere.

Beaver dams in Mediterranean ecosystems: trait‐specific effects on macroinvertebrates

AbstractAfter centuries of extinction due to human persecution, Eurasian beavers Castor fiber L. have been released to Southern Europe in the last decades. Being ecosystem engineers, beavers have attracted great attention regarding restoration of aquatic and terrestrial ecosystems. Nonetheless, the effects of the species on aquatic invertebrates known to date are not univocal and mostly refer to central European riverine systems. Here, we evaluated the effects of beaver presence on aquatic macroinvertebrates for the first time in a Mediterranean riverine ecosystem, by applying a sound control‐impact sampling design and controlling for seasonal variation in macroinvertebrate assemblage composition. A significant variation in response to season was evident for macroinvertebrate communities, revealing distinct assemblages during spring and summer. Furthermore, the presence of beavers was also identified as a significant driver of species composition, as samples near the beaver dam showed significant variation from control sites. Macroinvertebrate community traits changed according to the relative position to the beaver dam, as control sites featured on average higher abundances of taxa with higher values of bioindication score, larger size, lower adaptation to drag, and were less frequently of introduced origins. Yet, these differences were strongly taxon‐ and season‐specific in their intensity and direction. Differences across sites were mainly driven by the relative abundances of few taxa—including both alien species and high environmental quality indicators—such as those from genera Potamopyrgus, Baetis, Habrophlebia, Ephemerella, Leuctra, and Radix, which explained about 70% of the observed divergence among conditions. Our results indicate that beavers and their engineering activity may induce highly variable species‐specific responses in macroinvertebrates, thus possibly representing a driver of environmental heterogeneity along Mediterranean rivers, and that both bioindicators and alien species may exploit such heterogeneity.

Megabenthic Diversity Patterns on a Seamount in the Philippine Sea: Implications for Conservation Planning on the Kyushu-Palau Ridge.

The oligotrophic tropical western Pacific region is characterized by a high density of seamounts, with the Kyushu-Palau Ridge (KPR) being the longest seamount chain here. Effective spatial management plans for seamount ecosystems necessitate an understanding of distribution patterns and key environmental factors influencing benthic communities. However, knowledge regarding deep-sea biodiversity patterns over intricate topography remains limited. In this study, we investigated a seamount with a water depth of 522 m at the summit located in the southern section of KPR. Survey transects were conducted from 522 m to 4059 m. By analyzing video-recorded data obtained by a human-occupied vehicle (HOV) during dives and environmental variables derived from bathymetry, distinct assemblages were identified through noise clustering. α- and β-diversity patterns within the seamount megabenthic community were analyzed across the depth gradient, along with investigation of their environmental drivers. A total of 10,596 megafauna individuals were documented, categorized into 88 morphospecies and statistically separated into six distinct community clusters using noise clustering analysis. Species abundance and richness were highest within the 700-800 m water depth range, declining notably beyond 2100 m, indicating a critical threshold for habitat classification in this region. The β-diversity of megabenthic communities was high (0.836). Although β-diversity patterns along the depth gradient were mostly dominated by differences in species richness, the contribution of species replacement increased with depth, becoming dominant at depths greater than 3000 m. Depth emerged as the primary driver of spatial variation in community structure, while near-bottom current velocity, topographic parameters (bathymetric position index, slope), and substrate type also influenced the formation of microhabitats. The study highlights the depth gradients, thresholds, and other intricate environmental factors shaping the spatial heterogeneity of these communities. It provides valuable insights for the future development of effective survey and conservation strategies for benthic biodiversity on the KPR.

The impacts of fire vary among vertical strata: Responses of ant communities to long-term experimental burning.

Fire is a powerful tool for conservation management at a landscape scale, but a rigorous evidence base is often lacking for understanding its impacts on biodiversity in different biomes. Fire-induced changes to habitat openness have been identified as an underlying driver of responses of faunal communities, including for ants. However, most studies of the impacts of fire on ant communities consider only epigeic (foraging on the soil surface) species, which may not reflect the responses of species inhabiting other vertical strata. Here, we examine how the responses of ant communities vary among vertical strata in a highly fire-prone biome. We use a long-term field experiment to quantify the effects of fire on the abundance, richness, and composition of ant assemblages of four vertical strata (subterranean, leaf litter, epigeic, and arboreal) in an Australian tropical savanna. We first document the extent to which each stratum harbors distinct assemblages. We then assess how the assemblage of each stratum responds to three fire-related predictors: fire frequency, fire activity, and vegetation cover. Each stratum harbored a distinct ant assemblage and showed different responses to fire. Leaf litter and epigeic ants were most sensitive to fire because it directly affects their microhabitats, but they showed contrasting negative and positive responses, respectively. Subterranean ants were the least sensitive because of the insulating effects of soil. Our results show that co-occurring species of the same taxonomic group differ in the strength and direction of their response to fire depending on the stratum they inhabit. As such, effective fire management for biodiversity conservation should consider species in all vertical strata.

Multi-Stage Evolution of the Oceanic Lithosphere beneath Heard Island, Southern Indian Ocean

Abstract The Kerguelen Plateau is the second biggest submarine large igneous province (LIP) on Earth, however, the nature of the lithospheric mantle source underlying it remains poorly constrained. In this contribution, we provide novel insights into the oceanic lithospheric mantle underlying Heard Island (southern Indian Ocean), which represents the most recent and active phase of volcanic activity (<1 Ma) in the Kerguelen Plateau. We present petrographic and geochemical data for a suite of spinel-bearing harzburgite xenoliths hosted in basanite lavas and provide detailed constraints for distinguishing in situ mantle metasomatism from post-entrapment modification of the xenoliths following interaction with the host magma. We demonstrate that the xenolith mineral compositions and textures preserve a complex multistage history of different modal and cryptic transformations that occurred in the mantle due to: i) high degrees of partial melting that produced highly refractory whole-rock Mg# (Mg# = (Mg + Fe)/Mg × 100; 88–92), major element (FeO/MgO = 0.17) and mineral compositions (e.g. highly forsteritic olivine; Fo = (Mg + Fe)/Mg × 100; 91–92 mol %); ii) solid-state re-equilibration reactions during decompression that caused exsolution of clinopyroxene and Cr-spinel from xenolith orthopyroxene to form symplectite intergrowths; iii) cryptic metasomatism affecting the composition of xenolith clinopyroxene (i.e. enrichment in Na, Th, U and light rare earth elements, and depletion in Rb, Nb, Zr, Hf and Ti) due to interaction with carbonatitic melts in the mantle. Mantle fragments, entrapped by ascending basanite magmas as xenoliths were further modified by reactions with the host magma. This resulted in the partial dissolution of mantle orthopyroxene and replacement by newly formed and compositionally distinct assemblages of clinopyroxene (Mg# 87–91), olivine (Fo: 81–88 mol %) and Cr-spinel (i.e. ‘wehrlitisation’ of the xenoliths). This study highlights the utility of combining petrography and mineral chemistry to decipher the complex and sometimes overprinting and masking effects that different processes (e.g. melting events, metasomatism) exert on the lithospheric mantle, as well as constrain the processes that modify the xenoliths during transport towards the surface.

Biodegradation of thermoplastic starch by a newly isolated active microbial community: Deciphering the biochemical mechanisms controlling bioprocess robustness

Defining sustainable end-of-life routes for bioplastics comprises a task of outmost importance, while biological recycling constitutes the most favorable option for several biopolymers, such as thermoplastic starch (TPS). To our knowledge, this is the first study to assess the biodegradation of TPS pellets and films in aqueous cultures employing an acclimated microbial community. Biological treatment of bioplastics displayed a two-phase pattern that included different biodegradation rates, where TPS removal in the first phase remained high and decelerated in the second phase reaching a plateau. Thus, TPS weight reduction of 14.8 % was observed using pellets following 10 d of incubation, while although films exhibited higher reduction (slightly over 30 % in 15 d), the biodegradation rate was significantly reduced thereafter. Several changes of starch related bands were detected (using FTIR) in the surface of both pellets and films during the bioprocess, indicating induction of a common biodegradation pathway. Distinct bacterial assemblages were formed during the TPS biodegradation process and statistically significant differences were detected in the abundance of several genera between the two degradation phases. Fungal communities were more stable (Fusarium and Neocosmospora were dominant at all times) and there was no effect of biofilm or degradation phase on fungal community composition. Overall, a more diverse community incorporating lower catalytic activity was gradually formed, as confirmed by the shift between k-stategist and r-stategist taxa monitored, while crystalline over amorphous regions were enhanced in the biopolymer during TPS biodegradation, responses consistent with the biodegradation rate reduction observed in the plateau stage. The study highlighted the biochemical mechanism limiting TPS biodegradation processes and the significant potential of the newly isolated community in the development of TPS waste treatment technologies.

Linking divergence in phenotypic selection on floral traits to divergence in local pollinator assemblages in a pollination-generalized plant.

Divergent patterns of phenotypic selection on floral traits can arise in response to interactions with functionally distinct pollinators. However, there are a limited number of studies that relate patterns of phenotypic selection on floral traits to variation in local pollinator assemblages in pollination-generalized plant species. We studied phenotypic selection on floral traits of Viscaria vulgaris, a plant that interacts with a broad range of diurnal and nocturnal pollinators, and related divergence in phenotypic selection on floral traits to the expected level of divergence in local pollinator assemblages. We detected phenotypic selection on floral traits involved in the attraction of pollinators and the mechanics of pollen removal and deposition, and demonstrated that floral traits are subject to spatiotemporal variation in the strength and direction of phenotypic selection. We revealed that diurnal and nocturnal pollinators, when considered in isolation, mediated divergent patterns of phenotypic selection on floral traits. Consistent with the Grant-Stebbins model, we observed that divergence in phenotypic selection on floral traits increased with the expected level of divergence in local pollinator assemblages. Thus, generalized plant-pollinator interactions can mediate phenotypic selection on floral traits, and distinct local pollinator assemblages can generate a geographic mosaic of divergent patterns of phenotypic selection. We underscore that these outcomes are not exclusive to specialized plant-pollinator interactions and can emerge at a local geographic scale.

Diversity and structure of prokaryotic assemblages in a thermally stratified tropical lake

The structure and diversity of prokaryotic assemblages in inland waters are strongly related to their habitat. Yet, there is a lack of integrative studies surveying them in different compartments in tropical lakes. This study estimated the diversity and composition of prokaryotic assemblages in sediments, microbialites, and water column in the tropical warm monomictic Lake Alchichica and identified the most representative phylotypes while thermally stratified. The 16S rRNA gene survey showed a distinctive prokaryotic assemblage for each compartment, with 60–78 % of the phylotypes being unique to each one. Sediments accounted for the major prokaryotic diversity in the lake, with chemoorganotrophic bacteria and sulphate reducers as major biogeochemical components. Microbialites showed a high abundance of oxygenic and anoxygenic phototrophs, as well as organotrophs. The prokaryoplancton in the water column was mainly composed of picocyanobacteria and Flavobacteria in the epilimnion, shifting to a high diversity of anaerobic microorganisms in the hypolimnion. These water column assemblages were significantly correlated to pH, ORP, DO, and nutrient concentration. This study shows an integral view of the prokaryotic assemblages in a deep tropical lake related to physicochemical characteristics, from their diversity to their biogeochemical implications, suggesting the role of lake sediments as a possible microbial seed bank.

Retention forestry can maintain epiphytic lichens on living pine trees, but provides impoverished habitat for deadwood‐associated lichens

Abstract Managing forests for timber yields reduces the amounts of old trees and deadwood, which has profound effects on species that are dependent on them. Retention forestry, where some trees are permanently left unharvested on clear‐cut sites, may enable the formation of deadwood and old trees in managed forests, but it is unresolved how well these practices facilitate the occurrence of species in managed forests, especially in the long term. We studied the capacity of tree retention practices to support the diversity of epiphytic lichens, a key group among threatened forest species. We compared lichen assemblages on retained trees in harvested sites to those on trees in unharvested control sites. The data were collected 21‐year post‐harvest and included living trees, snags (standing dead trees) and logs (fallen trees) of Pinus sylvestris (Scots pine). Living trees, snags and logs each hosted distinct lichen communities. The highest lichen diversity was found on snags. On living trees, species richness was similar in harvested and unharvested sites, but there was slight species turnover. In contrast, deadwood in unharvested sites hosted higher species richness and distinct species assemblages compared to deadwood in harvested sites. These differences were most pronounced on snags. Specifically, unharvested sites contained high‐longevity snags (kelo trees), which hosted unique lichen communities with higher lichen richness than any other studied substrate, including the highest numbers of red‐listed and deadwood‐dependent species. Synthesis and applications. Retention forestry can support lichen assemblages associated with living Pinus sylvestris. However, maintaining deadwood‐associated lichen diversity through retention practices entails significant challenges. Deadwood‐associated lichen diversity relies on high‐longevity snags and is not sustained by the habitats provided in retention forestry. Biodiversity maintenance in forest management requires comprehensive provision of the habitat features of unmanaged forests, such as a qualitatively representative deadwood profile, which can prove difficult.

Taxonomic and abundance biases affect the record of marine eukaryotic plankton communities in sediment DNA archives.

Environmental DNA (eDNA) preserved in marine sediments is increasingly being used to study past ecosystems. However, little is known about how accurately marine biodiversity is recorded in sediment eDNA archives, especially planktonic taxa. Here, we address this question by comparing eukaryotic diversity in 273 eDNA samples from three water depths and the surface sediments of 24 stations in the Nordic Seas. Analysis of 18S-V9 metabarcoding data reveals distinct eukaryotic assemblages between water and sediment eDNA. Only 40% of Amplicon Sequence Variants (ASVs) detected in water were also found in sediment eDNA. Remarkably, the ASVs shared between water and sediment accounted for 80% of total sequence reads suggesting that a large amount of plankton DNA is transported to the seafloor, predominantly from abundant phytoplankton taxa. However, not all plankton taxa were equally archived on the seafloor. The plankton DNA deposited in the sediments was dominated by diatoms and showed an underrepresentation of certain nano- and picoplankton taxa (Picozoa or Prymnesiophyceae). Our study offers the first insights into the patterns of plankton diversity recorded in sediment in relation to seasonality and spatial variability of environmental conditions in the Nordic Seas. Our results suggest that the genetic composition and structure of the plankton community vary considerably throughout the water column and differ from what accumulates in the sediment. Hence, the interpretation of sedimentary eDNA archives should take into account potential taxonomic and abundance biases when reconstructing past changes in marine biodiversity.

Revisiting Clements and Gleason: Insights from Plant Distributions on Pikes Peak, Clements's Life-Long Study Site.

AbstractHow do species' distributions respond to their environments? This question was at the heart of the Clements-Gleason controversy, ecology's most famous debate. Do species respond to the environment in concerted ways, leading to distinct and cohesive assemblages (the Clementsian paradigm), or do species respond to the environment independently (the Gleasonian paradigm)? Using plant occurrences along the elevation gradient of Pikes Peak (Colorado) as a lens through which to gain insight into Clements's perspectives on the debate, we formally test for community patterns along this gradient using a modern framework unavailable at the time of Clements and Gleason. The Pikes Peak region was Clements's study area for more than 40 years, where he established a research lab and distributed sites along the elevational gradient. His investigations of plant distributions on this mountain likely influenced his views on communities. We found mixed support for the paradigms, with neither the Gleasonian paradigm nor the Clementsian paradigm fully supported. While distributions along the gradient showed evidence of clustering of species range edges, considered to be consistent with the Clementsian paradigm, the pattern was weak, and neither range edges nor species turnover peaked at ecotone elevations, as expected under the Clementsian paradigm. Our results illuminate the Clements-Gleason debate by allowing us to probe issues that complicate conclusively testing the paradigms, such as deciding on how we quantify environmental gradients and determining the appropriate scales for community patterns and processes that might generate them. Revisiting the debate also revealed that Clements's and Gleason's views had more in common than we realize. The debate may be less neatly resolved than we assume from mythos, and it continues to have relevance to basic and applied ecology today, as its legacy has shaped our (still tenuous) notion of ecological communities and the trajectory of our field.

Distribution patterns of micronektonic crustaceans (Decapoda, Euphausiacea, and Lophogastrida) in the tropical and subtropical Atlantic Ocean

Large pelagic crustaceans are a main component of the micronekton community in the deep-sea having an important role in the food webs and the biological carbon pump. However, they are scarcely studied in comparison to other groups such as mesopelagic fish. Here, we analyse day/night and bathymetric variability in taxonomic composition, abundance, and biomass across a latitudinal transect in the Atlantic Ocean from off Brazil (15°S) to the Canary Islands (25°N). A total of 95 species were identified belonging to 9 different families, of which Euphausiidae was the most abundant family and Acanthephyridae the family contributing the most to the total biomass. We found distinct assemblages associated with Atlantic ecoregions related to the environmental variables. Diel vertical migrations were detected along the entire transect, even crossing the oxygen minimum zone, likely due to the metabolic adaptations of these organisms.

The influence of burrow-generated pseudobreccia on the preservation of fossil concentrations

Burrowed discontinuity surfaces associated with condensed fossil concentrations demarcate breaks (hiatuses) in the Phanerozoic marine sedimentary record. Such intervals may be difficult to interpret in view of complex anatomy and varied fossil signatures. Transformation of a discontinuity surface into a heavily burrowed ‘pseudobreccia’ may further complicate the record, but this issue has remained unexploited to date. The richly fossiliferous Cretaceous–Paleogene (Maastrichtian–Danian) boundary interval exposed in Poland provides opportunities to test the influence of burrow-generated pseudobreccia on the preservation of associated hiatal fossil concentrations. Here, we document pseudobreccia anatomy and fossil-sediment relationships by three-dimensional X-ray computed tomography imaging. In the pseudobreccia zone, we identify a distinctive assemblage of late Maastrichtian fossils, which underwent subsurface preparation by burrowers in a hitherto unreported ichno-taphonomic process. Recognition of pseudobreccia is a prerequisite for the interpretation of the stratigraphy, sedimentology and fossil record of such intervals, which is of special interest for periods of major biotic turnovers, like the end-Cretaceous mass extinction.

Influence of hydrological variability and life history strategy on riverine fish assemblages in the Australian wet‐dry tropics

AbstractRiverine fish assemblages are strongly influenced by attributes of the flow regime. Tropical savannah river systems have distinct and predictable hydrologic seasonality, reflecting the wet‐dry climate, but can vary substantially in terms of dry season flow permanency and wet season flow‐pulse characteristics. Understanding how flow permanence and variability influence fish assemblages, and whether these factors can be used to predict responses to future hydrological change, are key knowledge gaps that impede effective management. We examined the influence of hydrological variability on the structure and diversity of freshwater fish assemblages across rivers of the wet‐dry tropics of northern Australia. We found distinct fish assemblages that varied predictably across three hydrological river types: Intermittent, Perennial Stable and Perennial Flashy flow regimes. This distinction emerged despite a common species pool across the region. Species richness was greatest in rivers with Perennial Stable flow regimes, whereas beta‐diversity was greatest in Intermittent rivers. However, life history strategies of constituent species were generally poor predictors of species abundances within each hydrological river type. The distinct fish assemblages evident among hydrological classes may provide some cautious ability to both predict potential fish assemblage changes with future hydrological changes (e.g. if perennial streams became more flashy or intermittent), and to predict fish assemblages expected in unsampled rivers with particular hydrological characteristics. Our findings provide further support for the importance of maintaining regional flow‐habitat heterogeneity and the connectivity between hydrological river types, and their essential role for conserving tropical fish species diversity into an uncertain hydrological future.