Researchers combined structured field surveys of non-ant Hymenoptera, a long-term ant dataset, museum collections, literature records and online sources. The integrated dataset contained 21,364 records. Its wasp dataset included 2,414 records from structured surveys conducted in 2018, 2019 and 2021, plus 10 opportunistic records from 2025. The ant dataset contained 15,502 records collected with multiple methods across 51 islands, islets and rocks from 2001 to 2012; museum and literature sources contributed 3,305 and 133 records, respectively.

The structured wasp survey covered Santa Cruz, Fernandina, Isabela, San Cristóbal, Floreana, Genovesa, Marchena, Pinta, Santiago and Española, spanning littoral, dry, transition and humid vegetation zones. Sampling effort included 146 Malaise units, 208 yellow traps and 174 net sweeps. The 2025 opportunistic collections were included in the taxonomic inventory but excluded from summaries and comparisons of the structured survey. Records were standardized under the Darwin Core standard, and specimens that could not be identified confidently to species were assigned morphospecies using consistent morphological characters and, where possible, comparison with reference material and consultation with taxonomic specialists.

The inventory added 20 species and 134 genera for the Galápagos, including 11 families not previously recorded there. The families with the greatest observed richness were Encyrtidae, Eulophidae, Formicidae, Scelionidae and Braconidae. Of the 524 species and morphospecies, 452, or 86.3%, belonged to groups with predominantly parasitoid biology; 370 of those 452 were morphospecies. The concentration of unresolved morphospecies in parasitoid groups identifies their species-level identities as a principal taxonomic gap.

Incidence-based richness models estimated more species and morphospecies than the 524 observed. Based on 93 occupied grid cells measuring 0.1° by 0.1°, the Bootstrap estimate was 595.47, the Jackknife 1 estimate was 673.38 and the Chao2 estimate was 658.26. These model estimates suggest that additional sampling and taxonomic work may document further diversity, but they do not identify a specific number of additional parasitoid species. Sampling methods also differed in the taxa they detected: among 394 species or morphospecies with a recorded method, 174 were detected exclusively by one method, including 129 recorded only with Malaise traps.

Observed species and morphospecies richness was associated with island area after accounting for sampling effort. A nonparametric Spearman partial correlation yielded rs = 0.63, p = 0.006 across 18 islands. Higher observed richness occurred on Isabela, Santa Cruz, Floreana, Santiago, San Cristóbal and Fernandina, while Wolf, Darwin, Tortuga and Seymour Norte had lower richness. The analysis identifies an association rather than demonstrating that island area causes the difference, and the authors noted that sampling methods and effort were uneven and some methods were taxonomically biased.

Most taxa were shared among islands and vegetation zones. Seven islands had no unique species or morphospecies, while Santa Cruz, Isabela and Pinta had the largest unique proportions at 18.9%, 16.4% and 11.3%, respectively. The humid zone had the highest proportion of unique taxa at 21%, compared with 15.3% in the dry zone, 9.2% in the transition zone and 8.9% in the littoral zone. A non-metric multidimensional scaling analysis found overlapping compositions, with stress = 0.12. Dry, littoral and transition zones overlapped particularly closely in the ordination, while the humid zone was most dissimilar in the associated cluster analysis.

Among the 137 named species, 61, or 44.5%, were classified as introduced, 30, or 21.9%, were endemic, five were native, two were cryptogenic and 39 had undetermined establishment status. The introduced proportion applies only to named species and may change as morphospecies are identified. The authors also noted that parasitoids can accompany introduced hosts, potentially contributing to records of non-native Hymenoptera.

The study provides an updated baseline for Galápagos Hymenoptera but is not a complete census. Its total exceeds the 486 Coleoptera species previously reported for the islands, although the Hymenoptera figure includes 386 morphospecies and the inventories differ in taxonomic resolution. The authors stated that further sampling and detailed study of parasitoid lineages may add species or morphospecies and improve knowledge of their identities, establishment status and distributions. The inventory also relied primarily on morphological evidence, which the authors said could be strengthened by taxonomic studies combining morphological and molecular approaches.

Subject of Research: Taxonomic inventory and distribution patterns of Hymenoptera in the Galápagos Islands

Article Title: Hymenoptera of Galápagos: diversity and distribution of one of the most species-rich insect orders in the archipelago

Article References: Picón-Rentería, P., Herrera, H. W., Avendaño, J. M., Tocora-Protz, M. C., Sánchez Restrepo, A. F., Fernández, F., Heraty, J. M., Bui, A. Y., Peck, S., & Sarmiento, C. E. (2026). Hymenoptera of Galápagos: diversity and distribution of one of the most species-rich insect orders in the archipelago. ZooKeys, 1294, 229-251. https://doi.org/10.3897/zookeys.1294.200001

Image Credits: AI Generated

DOI: 10.3897/zookeys.1294.200001

Keywords: Galápagos Islands, Hymenoptera, species inventory, parasitoid wasps, insect diversity, taxonomic gaps, morphospecies, island biogeography, vegetation zones, pagos, diversity, distribution

The Lagodekhi Protected Areas occupy the extreme northeastern corner of Georgia, on the southern slopes of the Caucasus Mountains, and span an altitudinal range from 590 to 3,500 meters above sea level. The complex combines the Lagodekhi Natural Reserve, established in 1912 largely through the efforts of the Polish forester and naturalist Ludwik Młokosiewicz, with an adjoining Managed Reserve, covering a total of roughly 24,000 hectares. The reserve protects one of the world’s best-preserved primeval deciduous forest habitats, a mosaic of lowland and montane forests, subalpine meadows and alpine zones that supports an extraordinary range of insect life. Because of this habitat diversity and a long history of entomological work, Lagodekhi is considered the best-studied protected area for insect diversity anywhere in the Caucasus region.

That reputation, however, rested on inventories that were far from complete. The first summary of the reserve’s insect diversity, published in 1956, listed 632 insect taxa. More recent updates had brought the total to about 1,790 species records, yet researchers suspected that the true number was vastly higher. The suspicion proved well founded: when material collected in 2014 was analyzed for parasitoid wasps of the family Ichneumonidae, the study yielded 313 new records for Lagodekhi, including 209 new country records. A parallel analysis of leaf beetles from the same material reported 48 species with 14 new country records. The new beetle survey, drawing on the same trapping program and supplemented by collections from recent years, extends that pattern dramatically across the order Coleoptera, one of the most species-rich groups of insects on Earth.

The technical backbone of the study was a network of malaise traps, tent-like interception devices that passively capture flying insects, operated at six sites spanning the full elevational gradient of the protected area. The lowest site stood in low-altitude forest at 666 meters, followed by mid-altitude forest at 847 meters, high-altitude forest at 1,351 meters dominated by Oriental beech, subalpine forest at 1,841 meters, subalpine meadow and scrubland at 2,230 meters, and finally the alpine zone at 2,559 meters. Traps at the four lower sites ran through the entire growing season from April to November 2014, while the two highest sites were sampled from May to early October because of harsher climatic conditions. Samples were collected roughly every ten days and preserved in 96 percent ethanol before sorting.

The malaise trap program was supplemented by two other standardized methods. Twelve-funnel traps, which intercept insects crawling and flying along tree trunks and stems, operated from early May to early August 2014, while Moericke traps, bright yellow pan traps that exploit the attraction of many insects to the color yellow, ran from early May to mid-June. These devices were installed at the same localities as the malaise traps, allowing direct comparison across habitats and elevations. The team also incorporated occasional hand collection carried out during field campaigns over the preceding decade, including nocturnal searches on dead beech snags, where several wood-associated species were found. Each record in the resulting species list documents the number of specimens, the sampling locality, the date, the collection method and the collectors, providing a verifiable voucher-backed baseline for future work.

Identifying the hundreds of captured specimens required international collaboration. Specialists from Poland and elsewhere examined particular families, including the hister beetles, ptinid beetles, minute brown scavenger beetles, sap-feeding beetles, rove beetles, jewel beetles, fungus beetles, weevils and click beetles, while the authors identified the remaining material. New records for the protected area and new country records were verified primarily against the multi-volume Catalogue of Palaearctic Coleoptera, the authoritative reference for beetle distributions across Europe, Asia and North Africa. The authors applied a deliberately conservative standard: where they could not locate an original source confirming a species’ presence in Georgia, and where no later confirmation existed, they excluded the record rather than risk inflating the country list. Voucher specimens are retained in the authors’ collections, and nomenclature was cross-checked against the Global Biodiversity Information Facility.

The results reveal a beetle fauna dominated by species tied to old-growth forest, dead wood and fungi, reflecting the primeval character of Lagodekhi’s habitats. Among the longhorn beetles alone, the survey added dozens of records, including species whose larvae develop in decaying timber, such as the large and distinctive Rhaesus serricollis, whose emergence holes were observed in decomposed beech snags. Iconic saproxylic beetles also appeared in the catches, among them the European stag beetle Lucanus cervus and its relative Lucanus ibericus ibericus, as well as the striking violet longhorn Rosalia alpina, a flagship species for the conservation of dead-wood habitats. Fungus-associated families flourished in the trap material: the pleasing fungus beetles of the family Erotylidae, the hairy fungus beetles, the minute tree-fungus beetles of the family Ciidae and the handsome fungus beetles all contributed new records, and a single nocturnal search on a bracket fungus produced 65 specimens of the pleasing fungus beetle Diaperis boleti.

Equally notable are the bark beetles and ambrosia beetles of the weevil subfamilies captured in the traps. Species such as Platypus cylindrus, the pinhole borer, appeared in large numbers across multiple sites and months, while others, including Xyleborinus saxesenii, Xylechinus pilosus and Anisandrus dispar, were recorded in Georgia for the first time. These tiny beetles bore into wood and, in the case of ambrosia beetles, cultivate fungal gardens inside their tunnels, playing crucial roles in the decomposition and nutrient cycling of forest ecosystems. Their detection in a primeval beech forest underscores how poorly known even ecologically pivotal groups remain in the South Caucasus, and how passive trapping methods can expose hidden components of the fauna that hand collection routinely misses.

The three families newly recorded for Georgia illustrate the global significance of the finding. Rhysodidae, represented in the survey by Omoglymmius germari, is a small family of slender, reddish predators that live in the galleries of fungi-infested wood. Sphindidae, with two Aspidiphorus species caught in the traps, comprises minute beetles that feed on slime molds. Thymalidae, documented through a single specimen of Thymalus aubei collected by hand, was previously unrecorded in the country altogether. Each of these records was flagged with the study’s double-asterisk convention for new country records, and each depends on the physical voucher specimen as its ultimate proof. In an era when distributional claims can circulate without evidence, the authors’ insistence on documented, verifiable specimens gives the new Georgian checklist a firm foundation.

The authors emphasize that their 195 species represent only a snapshot of the beetle diversity of Lagodekhi, gathered from a single intensive season and a handful of supplementary campaigns. Given the high landscape and habitat diversity of both the national park and Georgia as a whole, they expect future research to yield many more species new to the area and to the country. The study also carries a broader message for biodiversity science: even in regions with a century of entomological history, standardized, sustained and elevation-stratified sampling can still transform a national species list within a single year. For conservationists, the wealth of dead-wood-dependent beetles documented at Lagodekhi provides fresh evidence that protecting primeval forest habitats, as this reserve has done since 1912, preserves ecological communities that exist nowhere else in such intact form.

Subject of Research: Beetle diversity and new faunal records in the Lagodekhi Protected Areas, Georgia

Article Title: New records of Coleoptera from Lagodekhi Protected Areas, with new records for Georgia (Sakartvelo)

Article References: Japoshvili, G., Hilszczański, J., Byk, A., Jaworski, T., Łoś, K., Borowski, J., Tarwacki, G., Piętka, J., & Plewa, R. (2022). New records of Coleoptera from Lagodekhi Protected Areas, with new records for Georgia (Sakartvelo). Caucasiana, 1, 29-39. https://doi.org/10.3897/caucasiana.1.e85239

Image Credits: AI Generated

DOI: 10.3897/caucasiana.1.e85239

Keywords: Coleoptera, beetles, Lagodekhi Protected Areas, Georgia, biodiversity, new country records, Caucasus, malaise traps, saproxylic beetles, entomology, species inventory, forest conservation

Caddisflies are aquatic insects whose larvae build silk cases and retreats in streams, making them important players in freshwater food webs and widely used indicators of water quality. Adults are moth-like and nocturnal, drawn to lights along streams throughout the tropics. Because their larvae live in flowing water and are sensitive to pollution, sedimentation, and changes in flow, caddisfly assemblages are among the standard biological tools for assessing the health of rivers and creeks. A country that does not know its caddisfly fauna, the authors argue, cannot fully interpret its own environmental monitoring data.

The new paper is the third in a series of benchmarks stretching back decades. The first, published in 1992, tallied 168 species in 39 genera and 13 families. By 2015, contributions from foreign specialists—most notably Oliver S. Flint, Jr. of the Smithsonian Institution, along with Joaquin Bueno-Soria, Ralph Holzenthal, Roger Blahnik, and Steve Harris—had pushed the total to 257 species in 45 genera. The first species ever recorded from Panama, the hydropsychid Smicridea bivittata, was described by Hagen in 1861 from the Panama Canal Zone, and for the following century only three more species were added. The real acceleration came after 2015, when a resident-led effort took over.

That effort centers on the Aquatic Invertebrate Research Group, or AIRG, formed in 2018 from employees and research associates of the Museo de Peces de Agua Dulce e Invertebrados at the Universidad Autónoma de Chiriquí in David. Between 2015 and 2023, the group added two families, 11 genera, and 278 species—more than the previous 154 years of work combined. Roughly 70 percent of the species described or recorded before 2015 have since been re-collected and confirmed, which the authors say attests to the historical accuracy of the older records and the continued presence of those species in Panama.

The methodology behind the surge is deliberately unglamorous. The team relies primarily on ultraviolet light traps, using fluorescent tubes or LED strips, supplemented wherever possible by Malaise traps set at the same sites. The combination of the two methods has consistently produced the richest species inventories. Equally important is sampling duration: monthly collections from December through June have proven roughly equivalent to sampling all year, while a single visit to a site yields far too little information to characterize the species assemblage present. Multiple months and multiple methods, the authors stress, are the price of a realistic picture of freshwater diversity.

The scale of the task is enormous. Panama’s narrow isthmus, bridging North and South America, contains 6,326 named creeks and 1,387 named rivers, plus tens of thousands of unnamed streams, organized into 52 defined water basins. The country’s complex geology—two continental blocks, the Chorotega and Choco, shaped by subduction, volcanism, and uplift of the Cocos Ridge—has produced steep altitudinal gradients and a patchwork of microclimates that favor speciation. Before 2015, most collecting had been confined to a handful of spots such as Barro Colorado Island, Miramar, and the Fortuna Forest Preserve. In the past eight years, the team has sampled more locations across more altitudes than in the previous 145 years combined, though entire basins remain unsurveyed.

The standout story is the family Hydroptilidae, the micro-caddisflies, many barely a few millimeters long. Before 2015, Panama had 154 hydroptilid species; the count now exceeds 250, with the genus Neotrichia alone leaping from three species to 45. Remarkably, Panama now leads all Latin American countries in hydroptilid diversity, surpassing far larger nations such as Mexico and Brazil. The authors expect Brazil, with its vast area and dedicated cadre of specialists, eventually to overtake Panama—but not yet. They also report 30 to 40 additional candidate new species already in hand, awaiting formal description, and one provisional species, Metrichia PA-1, left unnamed because its headless holotype made formal diagnosis too risky.

Biogeographically, Panama’s fauna is overwhelmingly Central American. The country shares 285 species with neighboring Costa Rica—about 53 percent of its fauna—including 91 species once thought to be Costa Rican endemics. Jaccard similarity analyses suggest the true affinity between the two countries may be even higher than measured, because incomplete inventories in other Central American nations depress the calculated values. The authors estimate that adequately surveyed Central American countries would each record a minimum of 200 to 250 caddisfly species, and they argue that most of the region’s apparent faunal differences simply reflect disparities in scientific effort rather than genuine biological divergence.

Perhaps the most consequential finding is what the accumulation curves do not show. Plots of new species and new country records over time remain essentially straight lines, with no sign of leveling toward an asymptote. Even as new records of the larger, more conspicuous macro-caddisflies have slowed, the micro-caddisflies show no such falloff. Based on current trends, material in hand, and non-parametric estimators such as Chao2, the authors project that Panama will ultimately prove to host 750 to 850 species, most of them hydroptilids. The fauna is also highly endemic: 170 species, roughly 32 percent, are known only from Panama.

The team is now deliberately slowing its collecting to process a backlog of samples, including a 2023 effort that sampled 27 locations monthly across three altitudinal zones. Their agenda for the future is clear: mapping the surficial and altitudinal distribution of every genus and species, associating adults with their poorly known larvae, and moving from pure inventory into ecology, life history, and long-term monitoring. They also flag a caution for biomonitoring—year-to-year variation in adult assemblages is still so poorly quantified that detecting genuine environmental impacts from adult caddisflies alone may be difficult, and larval identifications, currently reliable only to genus, trade precision for lower noise. What began as a checklist has become a foundation for understanding how one of the tropics’ most biodiverse freshwater systems actually works, one tiny insect at a time.

Subject of Research: Diversity and biogeography of caddisflies (Trichoptera) in Panama

Article Title: The Trichoptera of Panama XXVII. The third benchmark—a waypoint to the future

Article References: Armitage, B. J., Harris, S. C., Ríos González, T. A., Aguirre, Y. P., Blahnik, R. J., Thomson, R. E., & Arefina-Armitage, T. I. (2024). The Trichoptera of Panama XXVII. The third benchmark—a waypoint to the future. Neotropical Biology and Conservation, 19(2), 253-291. https://doi.org/10.3897/neotropical.19.e113487

Image Credits: AI Generated

DOI: 10.3897/neotropical.19.e113487

Keywords: caddisflies, Trichoptera, Panama, biodiversity, freshwater insects, Hydroptilidae, Neotropics, taxonomy, species inventory, aquatic invertebrates, biogeography, water quality

The story of the checklist is itself a story of accelerating discovery. In 2003, the officially published figure for the reserve stood at 325 species. By 2012, that number had crept up to 331. In 2019, researchers reported 362 species, though three of those were escapees from households or private collections rather than genuinely wild birds. The first formal checklist in 2023 documented 365 species, and now, less than two years later, the total has jumped again to 373. Over roughly two decades, the recorded avifauna of the reserve has grown by about 13 percent, an increase the authors attribute not to birds suddenly appearing out of nowhere, but to people looking harder and seeing better.

That last point deserves emphasis. The researchers behind the new list point to a combination of factors driving the upward revision: a growing community of ornithologists and birdwatchers visiting the delta to ring and observe birds, dramatic improvements in optical equipment such as cameras and spotting scopes, and increased funding for monitoring projects. Rare birds that would once have passed unnoticed along the Black Sea coast or through the reedbeds of the fluvial delta are now photographed, documented, and reported through online platforms. The checklist project itself began in 2003 and has continued ever since, drawing on specialized literature stretching back to the mid-twentieth century, including decades of studies on numerical counts and rare-bird alerts, alongside contemporary online sources used with written permission.

The eight newly added species read like a roll call of avian wanderers. In taxonomic order they are the buff-breasted sandpiper (Calidris subruficollis), great spotted cuckoo (Clamator glandarius), European rock pipit (Anthus petrosus), Bonelli’s warbler (Phylloscopus bonelli), Radde’s warbler (Phylloscopus schwarzi), trumpeter finch (Bucanetes githagineus), little bunting (Emberiza pusilla), and, most remarkably of all, the ovenbird (Seiurus aurocapilla). Each of these represents an accidental record, a bird far outside its normal range or habitat, and none is yet supported by a dedicated scientific publication documenting its presence in the reserve. Instead, the evidence rests on press reports and online birding sources, which is why the new list omits the detailed qualitative and quantitative indices that accompanied its 2023 predecessor.

The ovenbird is the star of the update. This small, ground-nesting songbird breeds in the forests of North America and winters in Central and South America, making any appearance in Europe a sensation. One was recorded at Chituc on the Black Sea coast in 2023, and its significance goes beyond rarity: it belongs to the family Parulidae, the New World warblers, a family never before recorded in the reserve. With that single vagrant, the number of bird families documented in the Danube Delta Biosphere Reserve rose from 60 to 61. For a reserve on the western shore of the Black Sea, hosting a member of an essentially American family is a vivid illustration of how vagrancy can redraw biogeographic boundaries on paper.

The other newcomers tell their own stories of displaced migration. The buff-breasted sandpiper, another American species, was noted at the Tuzla and Nuntași lakes in 2020. The great spotted cuckoo, a southern European and African species, appeared at Sf. Gheorghe and the Lupilor sand levee in 2024. The rock pipit, a bird of rocky European coastlines, turned up at Sulina in 2022. Bonelli’s warbler was recorded at Chituc in both 2021 and 2024, while Radde’s warbler, a Siberian breeder, appeared at the Chituc sand levee in 2023. The trumpeter finch, a desert-dwelling species, was observed at Sf. Gheorghe as far back as 2016, and the little bunting, another Siberian, was recorded at Periprava and Sf. Gheorghe in 2024. The concentration of these records along the coastal sand levees and spits such as Chituc, Vadu, and Sacalin underscores how the delta’s shoreline acts as a funnel and first landfall for lost migrants arriving over the sea.

The revision was not only about additions. The authors also cleaned house, excluding seven species from the previous list. Four of these were escapes from households or private collections: the black swan (Cygnus atratus), Egyptian goose (Alopochen aegyptiacus), mandarin duck (Aix galericulata), and wood duck (Aix sponsa). The others were the Pallas’s sandgrouse (Syrrhaptes paradoxus), feral rock pigeon (Columba livia forma domestica), and oriental turtle dove (Streptopelia orientalis). Other candidate species, such as the Armenian gull (Larus armenicus) and the desert wheatear (Oenanthe deserti), were analyzed but rejected because the records came from just outside the reserve’s boundaries. The list also retains a haunting entry: the slender-billed curlew (Numenius tenuirostris), last recorded at Caraorman in 1992. A recent modeling study estimated a 96 percent probability that the species is already extinct, but because the IUCN still classifies it as critically endangered, the authors kept it on the checklist, a reminder that a list of species is also a ledger of losses.

The full picture that emerges is taxonomically impressive. The 373 recorded species belong to 61 families and 19 orders. Romania as a whole hosts 65 bird families and 19 orders, which means the Danube Delta Biosphere Reserve alone contains all of the country’s bird orders and all but four of its families. The systematics follow the framework proposed by Munteanu in 2001, the most recent comprehensive nomenclatural reference for Romanian birds. The list spans the full spectrum from familiar residents such as the mallard, coot, and great tit to icons of the delta like the great white pelican and Dalmatian pelican, the white-tailed eagle, and the pygmy cormorant, alongside a long tail of Arctic, Mediterranean, and Asian vagrants documented in recent years through the Rombird platform and coastal observation posts.

Why does an updated checklist matter beyond the satisfaction of a bigger number? The authors are explicit about the purpose: biodiversity lists are not only scientifically important but also underpin reports and presentations that rely on knowing the current number of species in a given area. Checklists feed into conservation planning, including the Natura 2000 network, since two Special Protection Areas, ROSPA0031 Danube Delta and Razim Complex–Sinoie and ROSPA0076 Black Sea, overlap with the reserve, and their Standard Data Forms depend on accurate species inventories. A reliable baseline also helps distinguish genuine range changes from mere gaps in knowledge, which is essential as climate shifts and habitat pressures reshape bird distributions across Europe.

The authors expect the list to keep growing. They plan to create an official online bird list for the reserve, a living document that can absorb new records as the number of ornithologists and birdwatchers in the delta continues to rise. Every season of improved optics, ringing effort, and coastal coverage seems to deliver new surprises, from American warblers to Siberian buntings. For now, the headline figure stands at 373 species across 19 orders and 61 families, a 13 percent increase in two decades, and a measure of both the extraordinary value of the Danube Delta for birds and the urgency of protecting it. The delta, it turns out, still has stories to tell, and the people counting its birds are finally equipped to hear them.

Subject of Research: Updated checklist of bird species recorded in the Danube Delta Biosphere Reserve, Romania

Article Title: An updated checklist of bird species in the Danube Delta Biosphere Reserve (Romania)

Article References: Marinov, M., Doroșencu, A.-C., Alexe, V., Bolboacă, L.-E., & Kiss, J. B. (2026). An updated checklist of bird species in the Danube Delta Biosphere Reserve (Romania). Scientific Annals of the Danube Delta Institute, 31, 1-14. https://doi.org/10.3897/saddi.31.161357

Image Credits: AI Generated

DOI: 10.3897/saddi.31.161357

Keywords: Danube Delta, bird checklist, biodiversity, ornithology, Romania, vagrant birds, ovenbird, birdwatching, Black Sea coast, Natura 2000, species inventory, conservation

The significance of the work lies in what foraminifera can reveal. Because the standing crop, diversity and species composition of benthic foraminiferal communities respond rapidly to shifts in salinity, pH, dissolved oxygen, organic matter input and anthropogenic stress, they serve as powerful bioproxies for ecological monitoring. Indices such as the FORAM Index, originally developed for coral reefs and later extended to estuaries, and Foram-AMBI, which assigns observed taxa to sensitivity eco-groups, depend entirely on accurate species-level taxonomy and region-specific reference data. Without a reliable local inventory, misidentification or missing baseline information can compromise the ecological interpretations drawn from these tools. The new study directly addresses that gap for a globally significant but understudied region.

The research focused on two contrasting mangrove systems. The first is the Indian portion of the Sundarbans, which covers 9630 square kilometres, of which 4267 square kilometres is forested, and hosts 24 species of true mangroves. Seven major rivers flow through the delta; the Hooghly and Mooriganga still receive freshwater from the Ganges-Brahmaputra-Meghna system, delivering the world’s second-largest freshwater input of roughly 42,000 cubic metres per second, surging to 138,700 cubic metres per second during the monsoon. The remaining five rivers have lost their freshwater connection to the Ganga and are tidally fed, producing a steady salinity gradient that rises towards the east. The second study area, the Budhabalanga estuary near Chandipur, is a smaller system dominated by Avicennia officinalis, Ceriops decandra, Rhizophora mucronata and Phoenix paludosa, and home to the mangrove horseshoe crab Carcinoscorpius rotundicauda.

Both systems face mounting pressure. Previous research has estimated that air temperature over the Sundarbans is increasing at 0.19 degrees Celsius per year, while relative sea level rises at close to 3.14 millimetres per year. The IPCC Sixth Assessment Report projects a further 0.5 degree Celsius increase in mean temperature and a 10 to 45 centimetre rise in sea level across the Sundarbans. A coastal vulnerability assessment of a 269 kilometre stretch of coastline found that approximately 42 percent falls within moderate to very high vulnerability categories. Against this backdrop, establishing which foraminiferal species persist, where they occur, and how assemblages differ between ecosystems provides an essential reference point for detecting future shifts.

Methodologically, the team compiled published studies that reported benthic foraminiferal assemblages from mangrove-associated environments with sufficient species-level taxonomic detail, excluding work that lacked such information or focused on non-mangrove settings. They then collected 112 sediment core samples across the region: 30 from Ajmalmari, Dulibasani and Chulkathi in the Sundarbans Biosphere Reserve between June 2019 and November 2020, four from Dhanchi in January 2024, 72 from Sagar Island between November 2021 and October 2022, and six from the Budhabalanga estuary between 2021 and 2022. Sampling took place at low tide from intertidal mangrove-associated mudflats using a hand-held vertical corer, 10 centimetres long and 3.5 centimetres in diameter, ensuring consistent sampling volume across sites.

In the laboratory, the uppermost 0 to 2 centimetres of each core were homogenised and subsampled, with roughly 10 cubic centimetres of sediment analysed in full. Specimens were stained with Rose Bengal at 1 gram per litre to distinguish living individuals, whose cytoplasm takes up the stain, from dead tests, and preserved in 70 percent molecular-grade ethanol. The sediment was wet-sieved through stacked 500 and 63 micrometre meshes, and the fraction larger than 63 micrometres was examined under an Olympus BX 53i bright-field microscope at 400 times magnification. Taxonomic identifications were verified against the World Register of Marine Species, the Foraminifera.eu database and established taxonomic references, with surface water temperature and salinity measured in triplicate at each site using calibrated instruments equipped with automatic temperature compensation.

The contemporary samples yielded a rich if modest picture. In the Sundarbans Biosphere Reserve, the team recorded 13 taxa, eight calcareous and five agglutinated, belonging to nine families, while Sagar Island yielded 14 taxa, ten calcareous and four agglutinated. Assemblages were dominated by small specimens under 500 micrometres, a feature typical of mangrove environments worldwide. The intertidal communities included the calcareous taxa Ammonia sp.1, Ammonia sp.2, Bolivina sp.1, Elphidium and Nonionella stella, the porcelaneous Quinqueloculina seminulum, and the agglutinated Entzia macrescens, Trochammina inflata and Textularia agglutinans. Notably, the standing crop of live tests was extremely low, below 3 percent in the Sundarbans and below 1 percent at Chandipur, meaning dead shells overwhelmingly dominate the assemblages, a pattern consistent with earlier regional studies and one that makes time-averaged death assemblages an effective basis for documenting regional species inventories.

To assess spatial structure, the researchers built a species-site occurrence matrix in which each taxon was coded as recorded in the literature, in the present study, or in both, then applied Bray-Curtis similarity analysis with UPGMA hierarchical clustering in the R statistical environment. The results were striking: the contemporary Sundarbans sites of Chulkathi, Ajmalmari, Dhulibhasani, Sagar Island and Dhanchi clustered tightly together, indicating broadly comparable assemblages despite differences in location and sampling period. The Chandipur site in the Budhabalanga estuary, by contrast, formed a separate cluster, reflecting differences in community composition even though several dominant taxa are shared. One species, the calcareous Asterorotalia pulchella, was recorded only at Chandipur and was absent from the Sundarbans assemblages, contributing to that separation.

The study’s interpretation of these patterns draws on global comparisons. Mangrove foraminiferal communities worldwide tend to be low-diversity and often dominated by agglutinated forms, as documented in Puerto Rican mangrove-lagoon systems, French Guiana’s Kaw estuary, Australian intertidal flats and Brazilian mangrove estuaries. Tidal elevation strongly influences the balance: agglutinated taxa such as Entzia macrescens and Trochammina inflata favour higher intertidal positions, while calcareous forms like Ammonia are common in mudflat zones. The co-occurrence of both groups in the Bay of Bengal samples is consistent with ecological zonation across mangrove microhabitats. The dominance of Ammonia species, described in the literature as opportunistic generalists with rapid reproduction and broad physiological flexibility, alongside the ecologically tolerant Quinqueloculina seminulum and the widespread agglutinant Entzia macrescens, underscores the resilience of a core regional species pool adapted to salinity fluctuations, organic enrichment and hypoxic conditions.

The authors are careful to acknowledge limitations. The compiled dataset integrates studies spanning different periods, locations and methodologies, which may introduce sampling bias and underrepresent rare, cryptic or seasonally restricted taxa, and shifting taxonomic nomenclature complicates species-level comparisons despite standardisation against contemporary databases. The study was not designed to quantify environmental drivers or seasonal variation, so interpretations remain qualitative. Even so, the strong agreement between historical records and new observations confirms the persistence of key taxa across years and sampling campaigns, and the discovery elsewhere of the endemic agglutinant Srinivasania sundarbanensis hints at undocumented diversity still awaiting description. What emerges is a robust, region-specific framework: a verified checklist of benthic foraminifera for the mangroves of the northeast Bay of Bengal that can anchor foraminifera-based ecological monitoring, sharpen biotic indices, and help conservationists track how these climate-stressed coastal ecosystems respond in the decades ahead.

Subject of Research: Benthic foraminiferal assemblages and their use as ecological indicators in Bay of Bengal mangrove ecosystems

Article Title: Inventorization of spatial patterns and reassessment of benthic foraminiferal assemblages from mangrove ecosystems of Bay of Bengal

Article References: Mandal, A., Ghosh, A., & Bhadury, P. (2026). Inventorization of spatial patterns and reassessment of benthic foraminiferal assemblages from mangrove ecosystems of Bay of Bengal. Discover Oceans, 3(1), Article 63. https://doi.org/10.1007/s44289-026-00169-7

Image Credits: AI Generated

DOI: 10.1007/s44289-026-00169-7

Keywords: benthic foraminifera, mangroves, Sundarbans, Bay of Bengal, Budhabalanga estuary, ecological monitoring, bioproxy, Bray-Curtis clustering, Ammonia, Entzia macrescens, sea-level rise, species inventory