Oceanic Islands Research Articles

Conservation management of an abandoned copra plantation at Palmyra Atoll, Northern Line Islands, Pacific Ocean

Coconut palms (Cocos nucifera) cultivated for copra are agricultural resources on many of the world’s low-lying tropical oceanic islands where they provide sustenance and economic value to human communities. However, coconut palms, when dominant in island plant communities, can outcompete native plants for above- and below-ground resources. Furthermore, when coconut palms displace native plant species preferred by seabirds as roosting and nesting habitats, they may disrupt beneficial nutrient pathways in both marine and terrestrial ecosystems. At Palmyra Atoll, located in the Northern Line Islands, Pacific Ocean, evaluation of three methods for controlling coconut palm seedlings (foliar herbicide application, cut-stem, and cut-stem combined with herbicide) showed that mortality was highest with the cut-stem combined with herbicide application. A comparison of herbicide volumes injected directly into stems of mature palms showed that mortality increased with herbicide volume; an injection of 10 ml of undiluted Roundup CustomTM herbicide (53.8% glyphosate) achieved 100% mortality within 8 months.

Oxygen Fugacity of Global Ocean Island Basalts

AbstractMantle plumes contain heterogenous chemical components and sample variable depths of the mantle, enabling glimpses into the compositional structure of Earth's interior. In this study, we evaluated ocean island basalts (OIB) from nine plume locations to provide a global and systematic assessment of the relationship between fO2 and He‐Sr‐Nd‐Pb‐W‐Os isotopic compositions. Ocean island basalts from the Pacific (Austral Islands, Hawaii, Mangaia, Samoa, Pitcairn), Atlantic (Azores, Canary Islands, St. Helena), and Indian Oceans (La Réunion) reveal that fO2 in OIB is heterogeneous both within and among hotspots. Taken together with previous studies, global OIB have elevated and heterogenous fO2 (average = +0.5 ∆FMQ; 2SD = 1.5) relative to prior estimates of global mid‐ocean ridge basalts (MORB; average = −0.1 ∆FMQ; 2SD = 0.6), though many individual OIB overlap MORB. Specific mantle components, such as HIMU and enriched mantle 2 (EM2), defined by radiogenic Pb and Sr isotopic compositions compared to other OIB, respectively, have distinctly high fO2 based on statistical analysis. Elevated fO2 in OIB samples of these components is associated with higher whole‐rock CaO/Al2O3 and olivine CaO content, which may be linked to recycled carbonated oceanic crust. EM1‐type and geochemically depleted OIB are generally not as oxidized, possibly due to limited oxidizing potential of the recycled material in the enriched mantle 1 (EM1) component (e.g., sediment) or lack of recycled materials in geochemically depleted OIB. Despite systematic offset of the fO2 among EM1‐, EM2‐, and HIMU‐type OIB, geochemical indices of lithospheric recycling, such as Sr‐Nd‐Pb‐Os isotopic systems, generally do not correlate with fO2.

Distribution pattern of Armadillidae species (Crustacea: Isopoda: Oniscidea) on the Izu Islands, Japan

Faunal studies of oceanic islands provide unique opportunities to study ecology and evolution. Four Armadillidae taxa were recorded from the Izu Islands, a group of oceanic islands off the coast of Japan. The distributions of these taxa and a phylogenetic tree are based on molecular data for 249 specimens from 88 sites. The Spherillo russoi (Arcangeli, 1927) species complex is distributed widely throughout these islands, and dispersal may have occurred via oceanic currents. On the nearby Izuoshima and Toshima Islands, Spherillo dorsalis (Iwamoto, 1943) may have recently migrated from the Izu Peninsula either via currents or been transported by human activity. In the middle islands, Shikinejima, Kozushima, Miyakejima, and Mikurajima, Venezillo hasegawai (Nunomura, 1991) was found, which may be derived from Spherillo obscurus (Budde-Lund, 1885) distributed in the Kanto region on the mainland. On the most southern and distant Hachijojima Island, Spherillo punctatus Nunomura, 2007 was found, and it does not differ genetically from specimens from Izenajima and Tokunoshima Islands in the Nansei Island Group, despite an approximate 1,000-km distance between them; this species may have been transferred by human activity. Our study showed that the Armadillidae assemblages in the Izu Islands were formed by several migration routes.

Frugivory and seed predation of fishtail palm (Caryota mitis Lour.) on the remote oceanic island of Narcondam, India

Abstract Oceanic islands, due to their evolutionary history and isolation, play a dual role of having high endemicity and being vulnerable to extinctions, with most known extinctions occurring on islands. Plant–animal interactions are particularly important on islands, as island systems generally have low redundancy and are more vulnerable to disruption either via extinction or by invasive species. Here, we examined the fruit removal and seed predation of a keystone palm, Caryota mitis, on Narcondam, a remote oceanic island. The island endemic Narcondam Hornbill (Rhyticeros narcondami) was the sole seed disperser of the palm (90 hours; N = 15 trees), with mean (± SE) visitation rate being 0.23 (± 0.06) individuals per hour and fruit removal rates of 3.5 (± 1.5; range: 0–16) fruits per visit, indicating a lack of redundancy in seed dispersal of the palm on this island. Whereas the invasive rodent, Rattus cf. tiomanicus, was the sole predator of palm seeds (N = 15 individual fruiting palms, 416 trap nights). Overall, 17.1% of the seeds placed (N = 375 seeds) were removed. Seeds placed under and away from the canopy, and at different densities (2 plots with 10 seeds each; 1 plot with 5 seeds, respectively), showed similar removal rates. This indicates density-independent seed predation and the lack of safe regeneration sites for Caryota mitis, with potential deleterious effects on subsequent stages of the ‘seed dispersal cycle’. Here, from a data-deficient site, we provide baseline information on the plant–frugivore interaction of a keystone palm and the potential impacts of an invasive rodent.

The conservation impact of botanical drones: Documenting and collecting rare plants from vertical cliffs and other hard‐to‐reach areas

Abstract A high percentage of island floras are at risk of extinction and have been reduced to relic populations, often in remote hard‐to‐reach areas. Uncrewed aircraft systems (UAS aka drones) are now being utilized to assist in the survey and collection of rare plants in inaccessible areas or vertical cliff habitats. Here, we test the application of this technology for conservation of 23 plant taxa in three oceanic island hotspots: Hawaiʻi, Madeira and the Republic of Palau. We collect high‐resolution imagery using a small UAS to document the distribution and abundance of vascular flowering plants. Location information is then used to map and assess plant populations. Depending on the terrain, collections are completed using either traditional rope techniques or newly developed remote drone‐based collection methods. Over the course of 6 years, we have greatly expanded our knowledge of rare and endangered species, while increasing survey efficiency and staff safety. Most importantly, this work has had a large impact on the conservation of critically endangered plants. Although using drones for botanical conservation comes with limits and challenges, we see great potential in the continued employment of these techniques wherever plants are growing on cliffs or in other hard‐to‐reach areas.

Carex chromosome numbers from Korean populations (eight taxa)

Carex L. is the most species-rich genus in Korean flora (ca. 180 taxa) as well as worldwide (more than 2,000 species). One of the hypotheses explaining high species diversity in the genus is holocentric chromosomes, which miss constricted centromeres during cell divisions; chromosome fission and fusion events are possible. To provide fundamental biological information, we report the meiotic chromosomes of eight Carex taxa investigated from twelve populations, which include four Ulleung-do Island (oceanic island) populations. The taxa and chromosome numbers observed were C. augustinawiczkii (n = 27<sub>II</sub>), C. bostrychostigma (n = 22<sub>II</sub>), C. egena (n = 25<sub>II</sub>), C. fusanensis (n = 21<sub>II</sub>), C. japonica (n = 31<sub>II</sub>, 32<sub>II</sub>), C. maackii (n = 37 II ), C. mollicula (n = 32<sub>II</sub>), and C. pediformis var. pedunculata (n = 36<sub>II</sub>). Chromosome numbers of C. augustinawiczkii, C. egena, C. fusanensis (a Korean endemic), and C. pediformis var. pedunculata are revealed for the first time. C. japonica from Ulleung-do Island populations exhibits two chromosome numbers, which differ from the chromosome numbers reported from the Korean mainland (peninsula). More chromosome data are required to understand Carex species diversity in Korean flora.

A glacial chronology for sub-Antarctic Marion Island from MIS 2 and MIS 3

It is increasingly apparent that local and regional factors, including geographic location, topography and climatic variability, strongly influence the timing and extent of glaciations across the Southern Hemisphere. Glacial chronologies of sub-Antarctic islands can provide valuable insights into the nature of regional climatic variability and the localised response(s) of glacial systems during periods of climatic change. With new cosmogenic 36Cl exposure ages from Marion Island in the southern Indian Ocean, we provide the oldest dated terrestrial moraine sequences for the sub-Antarctic islands. Results confirm that a local Last Glacial Maximum was reached prior to ∼56 ka when ice retreated with localised stand still events at ∼43 ka and between ∼38 and 33 ka. Evidence of ice re-advances throughout MIS 2 are limited and particularly absent for the cooling periods at ∼32 and ∼21 ka, and retreat continued until ∼17 ka ago. Any MIS 1 readvances on the island would be confined to altitudes above 900 m a.s.l. but the Holocene exposure ages remains to be documented. We compare Marion Island's glacial chronology with other sub-Antarctic islands (e.g., the Kerguelen archipelago, Auckland and Campbell islands and South Georgia) and review the evidence for a Southern Hemisphere glacial maximum in late MIS 3 (∼41 ka). At a regional scale we recognize sea surface temperatures, sea ice extent and the latitudinal position of the Southern Westerly Wind belt as key controls on equilibrium-line altitudes and ice accumulation due to their influence on air temperature and precipitation regimes. At an island scale, geomorphological mapping shows that deglaciation of individual glacier lobes was a-synchronous due to local physiographical and topographical factors controlling the island's micro-climate. We suggest that variability in deglaciation chronologies at smaller scales (particularly at the sub-Antarctic Islands) are important to consider when untangling climatic drivers across the Southern Ocean.

Chemical, Bioactive and antioxidant properties of Alhydwan (Boerhavia elegana Choisy) Seeds- A review

In recent years, consumers have turned to natural foods, but this is not the case. Since synthetic preservatives are harmful to health, consumers demand partial or complete replacement of synthetic preservatives. Because of this, there is an increasing demand for the development of more natural alternatives to improve food shelf life and safety. Strategies for natural protection are gaining popularity in food mapping. New preservation methods focus on using environmentally friendly organic plants with antioxidant and antimicrobial properties to extend the safety and shelf-life of food. Since ancient times, medicinal plants have been used in almost all cultures to treat many ailments around the world. The genus Boerhavia is found around the world in tropical, subtropical in nature and temperate climates, including Mexico, as well as the United States, Africa, Asia, Indian Ocean islands, Pacific islands, and Australia.  Boerhavia plants are widely used by locals and physicians to treat hepatitis, urinary tract disorders, gastrointestinal disorders, inflammation, skin problems, infectious diseases and asthma. This review focuses on the bioactive compounds of Boerhavia elegana Choisy.

Four distinct pulses of volcanism built the Melanesian Border Plateau: Implications for oceanic mid-plate superstructure formation

The ocean basins contain numerous volcanic ridges, seamounts and large igneous provinces (LIPs). Numerous studies have focused on the origin of seamount chains and LIPs but much less focus has been applied to understanding the genesis of large volcanic structures formed from a combination or series of volcanic drivers. Here we propose the term Oceanic Mid-plate Superstructures (OMS) to describe independent bathymetric swells or volcanic structures that are constructed through superimposing pulses of volcanism, over long time periods and from multiple sources. These sources can represent periods when the lithosphere drifted over different mantle plumes and/or experienced pulses of volcanism associated with shallow tectonic drivers (e.g. plate flexure; lithospheric extension). Here we focus on the Melanesian Border Plateau (MBP), one example of an OMS that has a complex and enigmatic origin.The MBP is a region of shallow Pacific lithosphere consisting of high volumes of volcanic guyots, ridges and seamounts that resides on the northern edge of the Vitiaz Lineament. Here we reconcile recently published constraints to build a comprehensive volcanic history of the MBP. The MBP was built through four distinct episodes: (1) Volcanism associated with the Louisville hotspot likely generating Robbie Ridge and some Cretaceous seamounts near the MBP. (2) Construction of oceanic islands and seamounts during the Eocene when the lithosphere passed over the Rurutu-Arago hotspot. (3) Reactivation of previous oceanic islands/seamounts and construction of new volcanos in the Miocene when the lithosphere passed over the Samoa hotspot. (4) Miocene to modern volcanism driven by lithospheric deformation and/or westward entrainment of enriched plume mantle due to toroidal mantle flow driven by the rollback of the Pacific plate beneath the Tonga trench. The combination of these processes is responsible for ∼222,000 km2 of intraplate volcanism in the MBP and indicates that this OMS was constructed from multiple volcanic drivers.

Geochronology, geochemistry, and tectonic setting of the Neoproterozoic magmatic rocks in Pan-African basement, West Ethiopia

The West Ethiopian plateau lies in the transition zone between the Arabian-Nubian shield and the Mozambique belt of the Pan-African orogen, underlain by Precambrian to Tertiary rocks in the Gimbi-Nejo area. The Precambrian basement consists mainly of intrusive-meta-intrusive and meta-sedimentary rocks with ice-rafting deposits. Based on the field survey, unique material records, deformation features, magmatism, and metamorphism indicate that the Gimbi-Nejo area likely underwent four tectonic stages during the Neoproterozoic era.The sedimentary formation of 980 ± 3.9 Ma rift valleys is represented by meta-clastic rocks, calc-silicate rocks, meta-basic rocks bearing marble in Chochi, and the Kata domain. Geochemically, meta-peridotite and meta-gabbros show tholeiitic features, while meta-granitoids are medium-K calc-alkaline peraluminous to metaluminous A-type (Ce/Nb 2.1–11.9; Y/Nb 1.2–8; Yb/Ta 2.6–14). Meta-gabbro samples with immobile HFSE (Th, Ta, Hf) and REE (La, Sm, Yb) fall in the within-plate alkaline basalt, oceanic island basalt (OIB), and continental rift basalt field. Meta-granitoid samples also fall in the within-plate granite field. The lithospheric subduction stage magmatic arc, composed of gabbros and granitoids, was emplaced around 827 ± 3.2 Ma. The granitoids include calcic tonalite and trondhjemite showing an adakitic signature with high Sr/Y (14.2–48.2) ratios. Gabbro samples fall in the island arc basalt and continental arc basalt field. Meta-peridotites and meta-gabbros to gabbros originated from the partial melting of garnet-spinel lherzolite to spinel lherzolite (<10 %) and garnet lherzolite to garnet-spinel lherzolite (<30 %) mantle source, respectively. The continental collisional area contains thrust folds and faults trending in a north–south direction. The ca. 797 ± 3.7 Ma calc-alkalic granitoid rocks along the suture zone are high-K peraluminous I-type granitoids (ASI < 1.1). The strike-slippage area is represented by sinistral ductile shearing deformation. The alkali-calcic granitoid rocks associated with shearing and decollements are low to high-K calc-alkaline peraluminous-metaluminous I-S type granitoids (ASI = 0.95–1.17). The U-Pb age of alkali-calcic granitoid is 564 ± 3.4 Ma. Syn-collisional calc-alkalic and late-post orogenic alkali-calcic granitoid samples both fall within the category of within the plate granite.The εHf (t) values of meta-granitoid (+9.4 to + 15.5), calcic granitoid (+7.6 to + 13.2), calc-alkalic granitoid (+7.4 to + 15.5), and alkali-calcic granitoid (+7.11 to + 17.12) suggest that these Neoproterozoic granitoids have been derived from a Meso-Neoproterozoic juvenile crust that formed through depleted mantle source. Depleted mantle magma likely ascended to the juvenile crust and remained there for a certain period (mean time = 122 Ma, 257 Ma, 248 Ma, and 256 Ma, respectively).

Investigations on geopolymer-based seawater sea-sand high performance concrete slabs reinforced with basalt FRP bars under direct contact explosions

Adopting locally available raw materials like seawater and sea-sand in coastal areas and oceanic islands has facilitated meeting the demands of marine engineering. However, these raw materials contain corrosive elements that could threaten the steel reinforcement in concrete structures, thus non-corrosive fibre-reinforced polymer (FRP) bars are proposed. In the present study, the geopolymer-based seawater sea-sand high performance concrete (G-SHPC) slab reinforced with basalt FRP bars was designed to preliminarily evaluate its dynamic behaviour under contact explosions. Tests were conducted on three large-sized slabs with different TNT charge weights, including 0.8 kg, 1.6 kg and 2.2 kg. To complement the experimental investigation, a numerical simulation was then performed in ANSYS-DYNA. A Continuous Surface Cap (CSC) model was developed to accommodate the unique characteristics of G-SHPC. Two different blast modelling methods, including the Arbitrary Lagrangian-Eulerian (ALE) algorithm and a hybrid Finite-Element (FE) and Smooth Particle Hydrodynamics (SPH) algorithm, were examined to faithfully reproduce the contact explosion phenomena. The structural models considered the bond-slip behaviour, and three bond-slip models were compared. The numerical results obtained through the ALE algorithm and the beam-in-solid bond-slip model exhibited fair agreement with the test results, with a maximum error of less than 6.3%. A parametric study was further conducted to establish the damage identification diagram. Formulas based on empirical data were formulated to anticipate the damage degrees of G-SHPC slabs exposed to contact explosions.

Bird‐flower colour on islands supports the bee‐avoidance hypothesis

Abstract Many insular plant species inhabiting different archipelagos worldwide present typical ornithophilous floral traits (e.g. copious nectar, red‐orange colours), but most of them are visited by insectivorous/granivorous birds and lizards, which act as generalist pollinators. Oceanic islands promote these ecological interactions mainly due to the scarcity of arthropods. Our goal is to understand how these generalist interactions contribute to the shift of floral traits from entomophily (mainland) to ornithophily or saurophily (island), where specialist nectar‐feeding birds have not inhabited. We used the well‐known pollination interactions occurring in the Canary Islands to evaluate two proposed ecological hypotheses, bee‐avoidance or bird‐attraction, explaining evolutionary transitions of floral traits. Specifically, we studied the flower colour conspicuousness of bird‐pollinated Canarian species visited by birds and lizards with their closest relatives from the mainland mainly visited by bees. We analysed the chromatic contrast of flower colours using visual models of bees, birds and lizards and the achromatic contrast in visual models of bees. We also compared reflectance spectra marker points of flowers with available spectral discrimination sensitivities of bees and birds. Using a phylogenetically corrected framework of independent plant lineages, our results revealed that bird‐pollinated Canarian species showed lower chromatic contrast according to bees and lizard visual models than their mainland relatives, but similar chromatic contrast for bird vision. In addition, reflectance spectra marker points of the Canarian species were displaced to the longest wavelengths, far from the wavelengths of maximum discrimination of bees, but close to birds. We conclude that the avoidance of bees would be a primary ecological strategy explaining the evolutionary transitions of flower colours from melittophily to ornithophily. The lower conspicuousness of bird‐pollinated Canarian flowers in lizards is perhaps a side effect of the bee‐avoidance strategy rather than an independent evolutionary strategy. Together, these findings provide insights into how vertebrate generalist pollinators can also lead to divergence of floral traits in insular habitats, but also in other arthropod‐poor habitats. Read the free Plain Language Summary for this article on the Journal blog.

Nest predation of Cory's shearwater Calonectrisborealis (Aves, Procellariiformes) by introduced mammals on Terceira Island, Azores.

The Azores holds the largest population of Cory's shearwater Calonectrisborealis (Cory, 1881) (Aves, Procellariiformes) in the world. Apart from a few mammal-free islets, the bulk of the population breeds in coastal areas on the main human-inhabited islands, where several non-native predators have been introduced. Throughout the entire year of the 2019 breeding season, we used motion-triggered cameras and regularly visited three colonies of Cory's shearwater to identify nest predators and the factors affecting nest predation. A total of 292,624 photos were obtained, of which 97.7% were of Cory's shearwaters, 1.7% of non-target species (e.g. other birds, rabbits) and 0.52% of potential predators. Of the monitored nests, 25.7% were predated (n = 9), mainly by black rats (n = 8), but also by cats (n = 1). The relative abundance of black rats in the nests was the main factor explaining nest mortality. This variable was significantly and negatively related with the daily survival rate of Cory's shearwater nestlings. Identification of the main nest predators is crucial for the management and conservation of native bird populations, particularly on oceanic islands, which harbour an important number of threatened and endemic species.

A carbon, nitrogen, and multi-isotope study of basalt glasses near 14°N on the Mid-Atlantic Ridge. Part B: Mantle source heterogeneities

Geochemical variations along mid-ocean ridges reveal the heterogeneous nature of the convecting upper mantle and geodynamic evolution of our planet (e.g., Hofmann, 2007; Parai et al., 2012). Although the occurrence of incompatible element and isotopically enriched mid-ocean ridge basalts (E-MORB) commonly arises from interaction with nearby mantle plumes, the source of E-MORBs far from known hotspots is debated. A well-known example of an enigmatic geochemical enrichment is found at 14°N on the Mid-Atlantic ridge (MAR). This is also one of the few locations worldwide where volatile-saturated E-MORBs, often referred to as “popping rocks” (PR), have been recovered. Although the mechanism(s) involved in popping rock generation remain elusive, compressional regimes associated with the exhumation and formation of oceanic core complexes (OCC) may be required to produce popping rocks via protracted volatile accumulation. However, the geochemical signature of OCC samples and their potential relationship to local geochemical enrichments associated with popping rock-affiliated MORBs remain unknown. Here, we present a comprehensive volatile characterization of popping rocks and associated MORBs (n = 19) sampled at 14°N on the MAR, including (n = 2) normal MORBs (N-MORB) from an oceanic core complex (OCC) and (n = 17) E-MORBs (Bekaert et al., Part A). We use isotopic and abundance data for volatile (carbon, nitrogen, noble gases) and radiogenic (Pb, Sr, Nd) elements, as well as the abundances of major and trace elements, to elucidate on the source(s) of E-MORBs at 14°N and discuss the potential origin(s) of geochemical heterogeneities within the upper mantle. We observe co-variations of helium and radiogenic element isotopes, suggesting potential contributions from a young HIMU-type (high μ = time-integrated 238U/204Pb) component in the OCC mantle source. The mantle source of the OCC samples is clearly distinct from that of PR-affiliated samples, suggesting no genetic relationship between OCC samples and E-MORBs. In addition, elevated Dy/Yb in OCC samples likely point to the incorporation of a subducted crustal component that is not observed in the mantle source of other MORB samples analyzed in this study. We report mantle source 40Ar/36Ar variations at 14°N, which, in line with previous studies, are interpreted as primarily reflecting variations in the amounts of recycled atmospheric Ar. Despite extensive evidence for drastic geochemical heterogeneities at 14°N on the MAR, we observe no significant δ15N variation (average δ15N = -4.49 ± 1.40 ‰) across N-MORB and E-MORB samples. This is a fundamental constraint, as the absence of significant N isotope variations across the upper mantle may imply that sedimentary N (with a typical δ15N ∼+6‰) is not extensively introduced within this reservoir during subduction. We investigate several scenarios that could explain this observation, including a significant contribution of altered oceanic crust to the overall budget of subducting slabs, quantitative return of subducting sedimentary N to the Earth's surface by arc volcanism, and/or preferential transport/preservation of sedimentary N in the lower mantle source of oceanic island basalts.

Mantle plumes sample heterogeneous mixtures of oxidized and reduced lithologies

Constraining the heterogeneity of oxygen fugacity (fO2) in the upper mantle is important for understanding the role of the deep Earth in determining the redox state of the atmosphere. Measuring the fO2 of primitive, mantle-derived basalts is a means with which to constrain mantle fO2 heterogeneity. Trace element systematics of 721 primitive olivine crystals from fifteen Icelandic picrites are reported, and these data are used with previously published bulk rock compositions to constrain their magmatic fO2. These fO2 values were compared with previously reported ocean island basalt (OIB) fO2 data calculated using identical methods, showing that fO2 is negatively correlated with parental magma MgO and positively correlated with bulk rock La/Yb, trends which were not evident in previous, smaller, global ocean island basalt datasets. These correlations cannot reasonably be the result of fractional crystallization, differential volcanic degassing, or differential partial melting of a typical homogenous mantle peridotite. Instead, differential partial melting of a heterogeneous source which preferentially sampled oxidized fusible lithologies at low melt fractions and diluted such signatures with depleted peridotite melts at high melt fractions likely caused the observed fO2-MgO-isotopic trends. These conclusions further reinforce that the mantle should not be modeled as a homogenous peridotite, but instead as a heterogeneous, non-equilibrated mixture of enriched “blebs” in a matrix of depleted peridotite, and that degree of partial melting is an important control on what portions of the mantle are detectable in igneous rocks.

Demographic responses of oceanic island birds to local and regional ecological disruptions revealed by whole-genome sequencing.

Disentangling the effects of ecological disruptions operating at different spatial and temporal scales in shaping past species' demography is particularly important in the current context of rapid environmental changes driven by both local and regional factors. We argue that volcanic oceanic islands provide useful settings to study the influence of past ecological disruptions operating at local and regional scales on population demographic histories. We investigate potential drivers of past population dynamics for three closely related species of passerine birds from two volcanic oceanic islands, Reunion and Mauritius (Mascarene archipelago), with distinct volcanic history. Using ABC and PSMC inferences from complete genomes, we reconstructed the demographic history of the Reunion Grey White-eye (Zosterops borbonicus (Pennant, 1781)), the Reunion Olive White-eye (Z. olivaceus (Linnaeus, 1766)) and the Mauritius Grey White-eye (Z. mauritianus (Gmelin, 1789)) and searched for possible causes underlying similarities or differences between species living on the same or different islands. Both demographic inferences strongly support ancient and long-term expansions in all species. They also reveal different trajectories between species inhabiting different islands, but consistent demographic trajectories in species or populations from the same island. Species from Reunion appear to have experienced synchronous reductions in population size during the Last Glacial Maximum, a trend not seen in the Mauritian species. Overall, this study suggests that local events may have played a role in shaping population trajectories of these island species. It also highlights the potential of our conceptual framework to disentangle the effects of local and regional drivers on past species' demography and long-term population processes.

Late Cretaceous basalts in the eastern South China Block: The result of slab tearing during retreating subduction of the Paleo-Pacific plate

Cretaceous arc-like, ocean island basalt (OIB)-like, and transitional basalts erupted on the eastern South China Block (SCB), and their petrogenesis was possibly related to the subduction of the Paleo-Pacific plate. However, the detailed petrogenesis in terms of slab subduction, magma sources, and the spatial distribution of the different types in the coastal and inland regions is poorly understood. Here we conduct a comparative study on the Late Cretaceous basalts from both coastal and inland regions. Our compiled age data demonstrate that the basalts in the coastal regions erupted in the period of 104–81 Ma. They show low Nb/La (<0.8), Nb/Y (<0.7), and other typical arc-like signatures, e.g., negative Nb-Ta anomalies, variable enrichment of LILE and LREE, and more radiogenic Sr-Nd isotopic compositions. In contrast, the basalts in the inland regions erupted at 86–71 Ma. They are characterized by high Nb/La (>0.9), slightly negative to positive Nb-Ta anomalies; they mostly possess positive εNd(t) values and geochemical features transitional to OIB-like basalts. The systematic geochemical differences may imply the spatial heterogeneity in their magma sources. The three end-member mixing model suggests that the isotopic signatures of arc-like basalts largely resulted from partial melting of the mantle wedge metasomatized by the subducted sediments, while those of transitional basalts likely resulted from depleted mantle source metasomatized by melts from altered oceanic crust (AOC) with minor sediments. We suggest that the retreating of the Paleo-Pacific plate promoted the melting of sediment-hybridized mantle wedge, and then triggered the opening of a slab window and asthenosphere-slab interactions.

Microplastics in the insular marine environment of the Southwest Indian Ocean carry a microbiome including antimicrobial resistant (AMR) bacteria: A case study from Reunion Island

The increasing threats to ecosystems and humans from marine plastic pollution require a comprehensive assessment. We present a plastisphere case study from Reunion Island, a remote oceanic island located in the Southwest Indian Ocean, polluted by plastics. We characterized the plastic pollution on the island's coastal waters, described the associated microbiome, explored viable bacterial flora and the presence of antimicrobial resistant (AMR) bacteria. Reunion Island faces plastic pollution with up to 10,000 items/km2 in coastal water. These plastics host microbiomes dominated by Proteobacteria (80 %), including dominant genera such as Psychrobacter, Photobacterium, Pseudoalteromonas and Vibrio. Culturable microbiomes reach 107 CFU/g of microplastics, with dominance of Exiguobacterium and Pseudomonas. Plastics also carry AMR bacteria including β-lactam resistance. Thus, Southwest Indian Ocean islands are facing serious plastic pollution. This pollution requires vigilant monitoring as it harbors a plastisphere including AMR, that threatens pristine ecosystems and potentially human health through the marine food chain.

A Residual Middle Triassic Oceanic Island-Seamount in the Maoershan Area, Northwest Tibet: Implications for the Evolution of the Paleo-Tethys Ocean

The assemblage of oceanic islands and seamounts, arising from the widespread presence of mature oceans, plays a crucial role in reconstructing the evolutionary history of the paleoocean. Oceanic islands or seamounts within the Longmuco-Shuanghu metamorphic complex, a remnant of the Paleo-Tethys Ocean in the central Tibetan Plateau, have seldom been reported due to their remoteness. This study has identified an oceanic island-seamount in the Maoershan area, situated to the west of the Longmuco-Shuanghu metamorphic complex, composed of basalt, diabase, limestone, and siliceous rocks. Based on field observations, petrology, zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotopes analyses, we have identified a suite of mafic rocks with OIB affinity. The youngest zircon U-Pb age cluster was concentrated at ~243–241 Ma. The geochemical characteristics of the siliceous rocks indicate a mixture of terrigenous material, suggesting that they formed in a continental margin. In combination with regional geological data, we conclude that the Longmuco-Shuanghu Paleo-Tethys Ocean remained open during the Middle Triassic. Furthermore, a fraction of the oceanic island-seamounts underwent scraping and transformed into a metamorphic complex, while other segments experienced deep subduction, resulting in the formation of high-pressure metamorphic rocks. Collectively, these processes gave rise to the distinctive high-pressure metamorphic complex within the central Qiangtang terrane.

It is not a mere piece of the mainland: Fluvial islands contribute to regional spider diversity in a seasonally flooded Amazonian archipelago

Abstract Islands and analogous insular habitats are found in several ecological contexts. With the exception of oceanic islands, however, the contribution of these insular habitats to regional biodiversity remains poorly investigated, especially in tropical regions. We investigated the understory spider assemblages in an Amazonian river archipelago to evaluate the contribution of fluvial islands to regional spider diversity. We collected spiders on 30 islands ranging from 1 to 1527 ha and at 23 sites in mainland habitats represented by continuous igapó flooded forests and terra firme forests. Spiders were collected by shaking the vegetation over a white sheet during a standardised time of 30 min. From 1404 adult individuals, we identified 290 spider species or morphospecies, with 150 species being recorded on the fluvial islands, 122 in the igapó flooded forests and 103 in the terra firme forests. Spider assemblages of fluvial islands exhibit lower alpha diversity and equitability compared with mainland habitats. The species composition of fluvial islands was significantly distinct from that of mainland habitats, even when compared with neighbouring igapó flooded forests. Several families and species of spider were significantly associated with a particular habitat, including 8 families and 10 species identified as indicators of fluvial islands. Fluvial islands effectively contribute to regional diversity since their spider fauna is not a mere impoverished subset of species from mainland habitats. Events that alter the flood pulse in Amazonian rivers (e.g., construction of hydroelectric dams) could threaten the unique biological assemblages of the floodplain habitats, especially the fluvial islands.