While the positive species–area relationship on islands is frequently observed, the mechanisms underlying this pattern remain poorly studied. By analyzing insular community diversity across spatial scales and the soil properties within the islands, we were able to explore potential mechanisms leading to the island species–area relationship of plants, as well as associated soil bacteria and fungi, from a tropical archipelago. We found that both plant and soil microbial communities showed similar positive species–area relationships across scales and the greater taxonomic diversity on larger islands was mainly driven by the higher richness within samples. These patterns arose primarily due to shifting habitat quality with island area, rather than spatial processes generally attributed to species–area relationships. Specifically, for plants, changes in soil total phosphorus content with island area were most explanatory, while changes in soil pH appeared to play the most important role in shaping soil bacteria and fungi patterns. By contrast, we found little evidence for the role of spatial processes (i.e. dispersal limitation or soil heterogeneity) within the island. Overall, this study highlights the importance of dissecting potential mechanisms underlying multi‐trophic community dynamics to explain patterns of biodiversity and its variation on islands.

The practice of beekeeping in Algeria is of great cultural, social, and economic importance. However, the importation of non-local subspecies reported by beekeepers has disrupted the natural geographical distribution area and the genetic diversity of the native honey bees. To assess the genetic diversity of A. m. intermissa and A. m. sahariensis, and their relationships with African and European subspecies, the COI-COII intergenic region was analyzed in 335 individuals, 68 sampled in Algeria, 71 in Europe, Madagascar, and the South West Indian Ocean archipelagos, and 196 sequences recovered from GenBank. The results show the presence of the A lineage exclusively in Algerian samples with the identification of 24 haplotypes of which 16 are described for the first time. These haplotypes were found to be shared by both subspecies, with A74 being the most common haplotype in the population studied. The sequence comparison indicates the existence of three polymorphisms of the COI-COII marker: P0Q, P0QQ, and P0QQQ. One new haplotype was identified in the M lineage in samples from France. No evidence of genetic introgression within the Algerian honey bee population was detected. These data enhance our knowledge of the genetic diversity and emphasize the importance of protecting these local subspecies.

Juan Fernández and Desventuradas are two oceanic archipelagos located in the southeastern Pacific Ocean far off the Chilean coast that received protected status as marine parks in 2016. Remoteness and access difficulty contributed to historically poor biodiversity sampling and limited associated research. This is particularly noticeable for bivalves, with most prior regional publications focused on single taxa or un-illustrated checklists. This study investigates marine bivalves collected between the intertidal and 415 m depth during (1) the 1997 IOC97 expedition aboard the M/V Carlos Porter, with special focus on scuba-collected micro-mollusks of both archipelagos, (2) two expeditions by the R/V Anton Bruun (Cruise 12/1965 and Cruise 17/1966), and (3) Cruise 21 of USNS Eltanin under the United States Antarctic Program, which sampled at Juan Fernández in 1965. Also, relevant historical material of the British H.M.S. Challenger Expedition (1873-1876), the Swedish Pacific Expedition (1916-1917), and by German zoologist Ludwig H. Plate (1893-1895) is critically revised. A total of 48 species are recognized and illustrated, including 19 new species (described herein) and six other potentially new species. The presence of two species mentioned in the literature for the region (Aulacomya atra and Saccella cuneata) could not be confirmed. The genera Verticipronus and Halonympha are reported for the first time from the Eastern Pacific, as are Anadara and Condylocardia from Chilean waters. Lectotypes are designated for Arca (Barbatia) platei and Mytilus algosus. These findings double the number of extant bivalve species known from the Juan Fernández and Desventuradas archipelagos, highlighting the lack of attention these islands groups have received in the past. A high percentage of species endemic to one or both archipelagos are recognized herein, accounting for almost 78% of the total. The newly recognized level of bivalve endemism supports the consideration of Juan Fernández and Desventuradas as two different biogeographic units (Provinces or Ecoregions) of the Eastern Pacific Ocean.

In his 1992 Nobel Prize acceptance speech, Derek Walcott imagines the broken vase and the subsequent reassemblage of its “African and Asiatic” fragments as a metaphor for Caribbean art forms, especially poetry. His vision of the particular archipelagic form of art that is invested in remaking from fragments, while specific to the Caribbean, is also visible in writing from other archipelagic spaces in the Indian Ocean. This article connects the Caribbean concept of the archipelago to the Indian Ocean through an analysis of the way Yvonne Adhiambo Owuor's The Dragonfly Sea (2018) and Amitav Ghosh's The Hungry Tide (2005) each present the littoral island spaces of the Indian Ocean. These texts construct alternatives to the possessive ontology of global capital through their articulation of the unique ontology and aesthetics of the Indian Ocean archipelago, borne out of the specificity of the littoral and its association with permeability, symbiosis, and a “back and forth” mirroring the tides themselves. The article argues that while Owuor's novel, like Walcott, is invested in the ontology and aesthetics of the archipelago as transformative and resistant, Ghosh's novel can be read with Braithwaite's concept of tidalectics as well as Glissant's creolization, to similarly depict the ontology and aesthetics of the archipelago as emerging out of fluidity and change rather than linearity or stasis.

Similar to other coastal regions worldwide, forests created by brown macroalgae have severely declined in recent decades across the Macaronesian oceanic archipelagos (northeastern Atlantic), eroding the provision of ecosystem services. However, the putative effects of natural and anthropogenic stressors (both local and global) on such declines across spatial and temporal scales remain unresolved. Our research endeavored to investigate the connection between local and global stressors and the distribution and extent of the brown macroalgae Gongolaria abies-marina in the rocky intertidal and adjacent subtidal zones of Gran Canaria over the past four decades. We also quantified the presence of populations at small scales, according to local micro-habitat topography (“open rock” versus “refuge”). Through herbarium records, we additionally analyzed the historical variation in the thallus size of the species. Finally, we experimentally assessed the thermotolerance of embryonic stages to warming. The main environmental drivers explaining the regression of G.abies-marina were the increasing number of marine heatwaves, while the number of local human impacts (quantified through the HAPI index) also accounted for further regression in the extent of marine forests. Warming experimentally reduced the survival and size of macroalgal embryos. A progressive miniaturization of the species, currently restricted to micro-habitat refuges as a survival strategy, seems likely to be the final stage in the progressive disappearance of this macroalgae from the island’s rocky shores.

Beta diversity patterns are essential for understanding how biological communities are structured. Geographical and environmental factors, as well as species dispersal ability, are important drivers of beta diversity, but their relative importance may vary across spatial scales. In this study, we evaluate whether beta diversity changes across geographical scales and analyse how different drivers affect turnover patterns of native seed plants in an oceanic archipelago, the Azores (Portugal). Using a 500 × 500 m resolution grid, we selected cells that are covered by one of the following habitats: native forest, naturalized vegetation and seminatural pastures. We calculated species turnover at three spatial scales: 1) between islands, 2) between cells within each island, and finally 3) between cells of each of the habitats of interest in each island. We then calculated the contribution of dispersal syndromes (endozoochory, epizoochory, hydrochory and anemochory) to turnover at each of the scales. Lastly, we assessed the relationship between geographical and climatic distances and habitat type with turnover. Turnover was higher at the smallest spatial scale, particularly in seminatural pastures, and decreased with increasing spatial scales, a pattern potentially associated with the historical fragmentation and current patchy distribution of native forest and seminatural habitats in the Azores. Dispersal syndromes and habitat type had a negligible effect on turnover at all scales. Geographical distance had a positive effect on turnover at all scales, increasing its importance with scale. The relationship between turnover and climatic distance was only significant at the intermediate and small scales in specific islands and habitats. Therefore, scale plays an important role at determining the effect of the drivers of turnover, in particular geographical and climatic distance. These results highlight the need to carefully select the scale of analysis when studying turnover patterns, as well as identifying the potential drivers associated with each spatial scale.

Assessing genetic diversity within species is key for conservation strategies in the context of human-induced biotic changes. This is important in marine systems, where many species remain undescribed while being overfished, and conflicts between resource-users and conservation agencies are common. Combining niche modelling with population genomics can contribute to resolving those conflicts by identifying management units and understanding how past climatic cycles resulted in current patterns of genetic diversity. We addressed these issues on an undescribed but already overexploited species of sardine of the genus Harengula. We find that the species distribution is determined by salinity and depth, with a continuous distribution along the Brazilian mainland and two disconnected oceanic archipelagos. Genomic data indicate that such biogeographic barriers are associated with two divergent intraspecific lineages. Changes in habitat availability during the last glacial cycle led to different demographic histories among stocks. One coastal population experienced a 3.6-fold expansion, whereas an island-associated population contracted 3-fold, relative to the size of the ancestral population. Our results indicate that the island population should be managed separately from the coastal population, and that a Marine Protected Area covering part of the island population distribution can support the viability of this lineage.

Oceanic islands constitute 0.05% of emerged land masses but account for 2% of UNESCO World Heritage Sites. Physical constraints have determined that the history of these remote territories is marked by globally unique forms of colonization and human cultures. A significant part of this heritage, located in coastal areas, is threatened by the mean sea level rise (SLR) due to anthropogenic climate change. This paper presents a regional approach to the risk estimation of SLR in the cultural heritage of oceanic islands, taking the Canary Islands (Spain) as an example. The Canary Islands is one of the most prominent oceanic archipelagos in the world (∼1500 km of coastline), where cultural heritage, preferentially located in the coastal areas (up to 50% in the first 1 km), nicely represents the two major stages of human occupation of islands (aboriginal and European). Through process-based modeling, high resolution flood maps were obtained for 20 climate scenarios and complete coverage of the archipelago. These maps were combined with detailed planimetries of 343 officially designated cultural heritage sites, applying damage functions to relate flood depth with the type of construction and the historical period. The results indicate potential damage to 55 cultural heritage sites of the Canary Islands which could be significant in 15 of them. For these cases, it is recommended to study specific adaptation measures aimed at mitigating the flood risk, such as moving the heritage assets away from the hazard areas or reinforcing and protecting the structures to reduce their vulnerability.

This study delves into the foraging ecology of the cookiecutter shark (Isistius brasiliensis) in the Saint Peter and Saint Paul Archipelago (SPSPA), assessing bite marks on pelagic fishes collected between March and September 2018. Examination of 200 individuals from five species revealed the shark's predilection for targeting adult fish, ensuring efficient removal of energy-rich tissue layers. However, a notable exception is Thunnus albacares, preyed on predominantly during its juvenile stage, possibly due to vertical spatial segregation. Recent bites were pervasive across species, with wahoo displaying a distinctive pattern. Cookiecutter shark bites predominantly targeted the lateral body portion (>55%) except for yellowfin tuna, which exhibited a preference for the ventral region (95%). The estimated length distribution suggests the SPSPA as a potential nursery area for cookiecutter sharks. Bite mark positions and frequencies may be linked to fish behavior, swimming velocity, and fishing gear strategy, highlighting the complex interplay in pelagic ecosystems.

Biogeographical relationships between the Canary Islands and north-west Africa are often explained by oceanic dispersal and geographical proximity. Sister-group relationships between Canarian and eastern African/Arabian taxa, the 'Rand Flora' pattern, are rare among plants and have been attributed to the extinction of north-western African populations. Euphorbia balsamifera is the only representative species of this pattern that is distributed in the Canary Islands and north-west Africa; it is also one of few species present in all seven islands. Previous studies placed African populations of E. balsamifera as sister to the Canarian populations, but this relationship was based on herbarium samples with highly degraded DNA. Here, we test the extinction hypothesis by sampling new continental populations; we also expand the Canarian sampling to examine the dynamics of island colonization and diversification. Using target enrichment with genome skimming, we reconstructed phylogenetic relationships within E. balsamifera and between this species and its disjunct relatives. A single nucleotide polymorphism dataset obtained from the target sequences was used to infer population genetic diversity patterns. We used convolutional neural networks to discriminate among alternative Canary Islands colonization scenarios. The results confirmed the Rand Flora sister-group relationship between western E. balsamifera and Euphorbia adenensis in the Eritreo-Arabian region and recovered an eastern-western geographical structure among E. balsamifera Canarian populations. Convolutional neural networks supported a scenario of east-to-west island colonization, followed by population extinctions in Lanzarote and Fuerteventura and recolonization from Tenerife and Gran Canaria; a signal of admixture between the eastern island and north-west African populations was recovered. Our findings support the Surfing Syngameon Hypothesis for the colonization of the Canary Islands by E. balsamifera, but also a recent back-colonization to the continent. Populations of E. balsamifera from northwest Africa are not the remnants of an ancestral continental stock, but originated from migration events from Lanzarote and Fuerteventura. This is further evidence that oceanic archipelagos are not a sink for biodiversity, but may be a source of new genetic variability.

Abstract Synthesising knowledge on the health of marine ecosystems and the human activities is crucial to informing holistic marine management. In many coastal states, however, research is conducted in an ad hoc manner and rarely compiled into accessible repositories making it challenging for marine managers to identify knowledge gaps when allocating resources. Here we conduct a structured review of existing literature to identify the current state of marine and coastal knowledge in the Isles of Scilly, an oceanic archipelago in the UK. The archipelago's marine flora and fauna are biogeographically unique in the Northeast Atlantic, with a distinct mosaic of warm and cold temperate habitats and species and are also considered a rare example of a near pristine marine environment in the otherwise highly degraded Northeast Atlantic Ocean. We found 150 sources relating to the marine biodiversity and relevant human activities in the Isles of Scilly with increasing diversification of research topics in recent years. Sources however remain dominated by specific taxa and habitats, suggesting the Isles of Scilly would particularly benefit from future research into: (1) anthropogenic impacts associated with warming waters and intense seasonal vessel activity; (2) development of repeatable survey protocols that can underpin long-term, ecosystem-based monitoring and management (notably for reef and sediment habitats and the European spiny lobster); and (3) data gaps associated with marine teleost fish and elasmobranch communities including identifying core habitat. This review can therefore act as a baseline biological synthesis for the region and importantly, can inform future research priorities.

Abstract The Ogasawara Islands are a highly isolated oceanic archipelago in the Pacific Ocean that possess unique faunal and floral biodiversity with a high level of endemism. As historically more focus has been put on the terrestrial realm in examining diversification and evolutionary processes on oceanic islands, publicly accessible and spatially resolved data of marine reef ecosystems remain scarce. To address this issue, we conducted the first environmental DNA (eDNA) metabarcoding surveys of the actinopterygian (ray‐finned) and elasmobranch fishes and of Scleractinia coral assemblages in the waters of the Ogasawara Islands. We detected a total of 124 unique taxa of fish and 38 unique taxa of scleractinian corals. Overall, our eDNA results confirmed that the Ogasawara Islands host a rich variety of coral and fish fauna and underline the strength of eDNA surveys in rapidly obtaining targeted multi‐taxa data using seawater samples, requiring comparatively little effort and a lack of requirement for in situ taxonomic expertise. We anticipate that continued biomonitoring using eDNA with high sampling effort will add to and complement the body of knowledge regarding species distributions, invasive species, and biodiversity hotspots within oceanic archipelagos.

Abstract QuestionsOceanic islands are global hotspots of endemism and evolutionary radiations but many have been severely degraded by human activities and biological invasions. We evaluated the pace and direction of the natural recovery of ecosystems over 77 years across a subtropical oceanic archipelago including islands of various size, elevation, histories of human settlement and deforestation, and invasions by non‐native plants and mammals. This information is essential to guide the ecological restoration of the archipelago.LocationForest vegetation on nine of the Ogasawara Islands in the northwestern Pacific Ocean.MethodsWe first digitized historical vegetation data of the Ogasawara Islands collected during field surveys in 1935. Then, after checking their species compositions, we integrated past and present plant community types. Finally, we identified the landscape‐scale changes in forest vegetation by comparing vegetation maps from 1935, 1979 and 2012.ResultsOver 77 years, the vegetation trajectories of each island varied depending on the introduction of invasive alien species and the remaining proportion of native forest, the latter of which had a strong influence on the recoverability of native forest.ConclusionsOur results highlight the importance of the history of invasive species introductions and the remaining proportion of native forest—both of which reflect the intensity of anthropogenic disturbance—in determining the degree of human intervention needed for restoration on oceanic islands.

Abstract The ecological and phenotypic diversity observed in oceanic island radiations presents an evolutionary paradox: a high level of genetic variation is typically required for diversification, but species colonizing a new island commonly suffer from founder effects. This reduction in population size leads to lower genetic diversity, which ultimately results in a reduction in the efficiency of natural selection. What then is the source of genetic variation which acts as the raw material for ecological and phenotypic diversification in oceanic archipelagos? Transposable elements (TEs) are mobile genetic elements that have been linked to the generation of genetic diversity, and evidence suggests that TE activity and accumulation along the genome can result from reductions in population size. Here, we use the Hawaiian spiny-leg spider radiation (Tetragnatha) to test whether TE accumulation increases due to demographic processes associated with island colonization. We sequenced and quantified TEs in 23 individuals representing 16 species from the spiny-leg radiation and four individuals from its sister radiation, the Hawaiian web-building Tetragnatha. Our results show that founder effects resulting from colonization of new islands have not resulted in TE accumulation over evolutionary time. Specifically, we found no evidence for an increase in abundance of specific TE superfamilies, nor an accumulation of ‘young TEs’ in lineages which have recently colonized a new island or are present in islands with active volcanoes. We also found that the DNA/hAT transposon superfamily is by far the most abundant TE superfamily in the Tetragnatha radiation. This work shows that there is no clear trend of increasing TE abundance for the spiny-leg radiation across the archipelago chronosequence, and TE accumulation is not affected by population oscillations associated with island colonization events. Therefore, despite their known role in the generation of genetic diversity, TE activity does not appear to be the mechanism explaining the evolutionary paradox of insular diversification in the Tetragnatha spiny-leg radiation.

Abstract The oceanic archipelago of Fernando de Noronha represents one of the most important regions for Brazilian marine biodiversity, and is considered a ‘no-take’ marine area under law. More than 130 crustacean species have already been registered in the archipelago, with a significant number of caridean shrimps. Almost half of these shrimps belong to the family Alpheidae, making them an important marker of the species composition of the region. This study provides five new records of alpheids for the archipelago. Samples were taken in 2019 and 2022 from six locations around Fernando de Noronha, using active search during low tide and SCUBA diving in subtidal zones. The new records are Alpheus agilis, A. angulosus, A. rudolphi, Automate dolichognatha sensu lato, and Salmoneus ortmanni, and their DNA sequences have been made available alongside geographical distribution, photographs, ecological notes, and species remarks. All DNA sequences (mitochondrial 16S and cytochrome oxidase I genes) generated were compared with sequences available in Genbank and, in some cases, our sequences are the first for the species. Through this update, a total of 46 species of caridean shrimps have been recorded from Fernando de Noronha. Here we highlight the importance of checklists as a tool to keep an updated record of species' distributions. Continuous study of the native fauna of one of the most important biodiversity hotspots on the Brazilian coast is essential to establish effective management and conservation plans for the region.

Multiple island effects shape oceanographic processes and zooplankton size spectra off an oceanic archipelago in the Tropical Atlantic

The Kerguelen archipelago, one of the largest oceanic archipelagos in the world, was built by an active hotspot interacting with a ridge between 110 and 40 million years ago; since then, the ridge has migrated over 1000~km away and the archipelago's volcanic activity has been steadily decreasing. Despite the lack of recent active tectonics and the quiescent volcanism of the Kerguelen archipelago, there have been several observations of seismic events of unknown origin in its vicinity. The only seismic instrument within 1000~km of the archipelago was installed on Kerguelen's main island in the 1980's. In this study we apply modern earthquake detection techniques to the continuous waveforms recorded by this seismometer over the past 20 years. We reveal that the Kerguelen archipelago islands hosts an abundant seismicity. This seismicity exhibits swarm-like characteristics in several clusters while at other locations the earthquakes appear more steady over time. We locate most events near the largest icecap of the main island. We speculate that the origin of the earthquakes can be linked to residual volcanic, magmatic, or hydrothermal activity at depth, all of which can be favored by flexural stress caused by the documented fast retreat of icecap. This seismicity may also indicate that the Kerguelen hotspot shows signs of unrest.

For the first time, Clusiidae (Diptera) species are recorded from the oceanic Archipelago Fernando de Noronha, Brazil. They are represented by three genera and seven species: Czernyola fumialula sp. nov., Heteromeringia czernyi Kertsz, 1903, Sobarocephala araujoi sp. nov., S. finnilaei Frey, 1918, S. icmbio sp. nov., S. protea Lonsdale & Marshall, 2012, and S. sp. For S. icmbio sp. nov., the aggregation behavior at night was observed on the undersides of broad leaves, females contained an average of 71 eggs, and flight interception traps correlated a positive linear relationship with precipitation seasonally. An illustrated key is presented for all species of the Archipelago.

The 'western seed bug', known as Leptoglossusoccidentalis, is considered a global invasive species that has experienced a recent rapid expansion worldwide, becoming an important pest species for coniferous forests. With the 'Canary Islands early-warning network for the detection and intervention of invasive exotic species' (RedEXOS), this species was detected for the first time in the Canarian archipelago in an urban area in the eastern part of the island of Gran Canaria. This early detection is crucial for understanding the potential damage in one of the islands with the highest surface area of natural endemic pine forest.

Tropical islands harbour a disproportionally high number of endemic species, which face increasing threats due to habitat loss, disturbance and introduced alien predators. Long-term demographic studies are needed to understand how such threats may impact on population productivity. We report an investigation of a key demographic parameter, nest survival, over a 13-year period in a small ground-nesting shorebird on the island of Maio (Cabo Verde). Similar to many tropical islands, Maio is expected to face increased tourism, disturbance, and potential loss of nesting habitats. We monitored over 700 nests of the largest, year-round resident breeding population of Kentish plover in the Atlantic Ocean archipelago. Our work produced three important findings. First, we show that nest survival differed among the major habitats of the main breeding site, the Salinas do Porto Inglês, because nests in the salt-extraction area had higher daily survival rates DSR = 0.9654 ± 0.0076 SE than nests in grasslands DSR = 0.9557 ± 0.0038 SE. The salt-extraction is a dynamic habitat that is naturally regulated by rainfall and sea water inflow and managed with traditional methods for salt-extraction. Kentish plovers breed on small islets surrounded by salty water where mammalian predators may have restricted access. Second, we found that breeding densities of plovers decreased from 0.11 nests/ha to 0.03 nests/ha over 13 years. Last, we show that nest survival declined from 0.9784 ± 0.0107 in 2007 to 0.8967 ± 0.0401 in 2019. We suggest that the declining breeding density and nest survival may be driven by a combination of ecological factors including predation by native and introduced species, and by increased human disturbance. To help maintain sustainable levels of nest survival and to ensure long-term persistence of this Kentish plover population, we propose to incorporate traditional Salinas management into direct conservation actions, to reduce human disturbance and manage nest predators to help nest survival on tropical islands.