The investigated sites were Parque de los Cenotes, Cenote Cauich, La Hondada and a fourth aguada-type cenote in Cancun, in the northern part of the Yucatán Peninsula. Parque de los Cenotes was classified as a mixture of cavern and aguada types, Cenote Cauich as a grotto or pitcher-type cenote, and the other two sites as aguada-type cenotes. These water bodies occupy an ecological context that has received less attention than cenotes associated with tourism, rural areas or dense jungle.

Some urban cenotes lie in public parks, between busy avenues or on private property, and the article notes that some contain litter, discarded tires and electrical waste. The researchers selected four sites to examine species richness, community structure and composition, with a particular focus on phytoplankton and protists. These groups had remained incompletely characterized in cenotes in the Mexican Caribbean, where the broader freshwater and marine biodiversity of the region is also poorly studied.

The design was observational rather than experimental: it described what was present at four locations across two seasonal periods, without manipulating environmental conditions or testing the effects of specific pollutants. The authors described microbial diversity as a potentially useful indicator of ecosystem condition, while also emphasizing that identifying organisms suitable as indicators of eutrophication or environmental impact remains difficult without more comprehensive data. At each sampling station, researchers collected two 10-liter water samples.

Material larger than 150 micrometres was removed with a plankton net, and the retained material was suspended in 300 milliliters of water collected from the same cenote and stored in sterile 500-milliliter screw-cap bottles. One sample was fixed with 4% Lugol solution, while the other was analyzed fresh, using a modified method. Samples were kept at room temperature for no more than 24 hours, passed through a 45-micrometre membrane, and the material retained by each membrane was resuspended in 1 milliliter of distilled water for observation as soon as possible.

Optical microscopes equipped with 10-, 40- and 100-fold objectives were used to identify and document organisms, and photographs were recorded with a camera. Taxonomic assignments were based on established identification keys and reference resources. Abundance was calculated from the organisms counted in the concentrated preparation and the volumes used for concentration, counting and sampling, with results expressed as organisms per liter or milliliter.

Inventory completeness was assessed with species-accumulation curves and the ACE Mean and Chao 1 Mean estimators, which use singleton and doubleton records to estimate how thoroughly the samples represent the communities. Rank-abundance curves were used to examine community structure, including the relative representation of dominant and rare taxa. Within-site diversity was summarized with the exponential Shannon-Wiener index, which expresses the effective number of species.

Ward’s method was used to construct a cluster analysis for assessing similarity among the four communities. The researchers also calculated the percentage dissimilarity in diversity between pairs of sites. Together, these methods assessed not only which organisms were detected, but also how evenly the records were distributed and how much the four aquatic communities differed from one another.

Across the four cenotes, the survey registered six phyla, four subphyla, 10 classes, eight subclasses, 15 orders, 15 families and 18 genera. The inventory contained 17 identified species and four forms that could not be determined beyond the species level. Eight of the 17 identified species were phytoplankton, approximately 47% of the identified total, while nine were protists, approximately 53%.

The named organisms belonged to Euglenophyta, Heterokontophyta, Bacillariophyta, Cyanobacteriota, Ciliophora and Amoebozoa, including euglenoids, diatoms, cyanobacteria, ciliates and amoeboid protists. The study contributed 11 new records for the Yucatán Peninsula. These included the named species Euglena mutabilis, Lepocinclis acus, Phacus orbicularis, Coscinodiscus radiatus, Oscillatoria limosa, Arcella gibbosa, Amoeba radiosa and Mayorella vespertilioides, together with genus-level records for Vorticella, Aspidisca and Coleps.

The authors noted that most of the protist records except Paramecium aurelia were also reported for the first time in the Mexican Caribbean. Species-accumulation estimates indicated relatively high completeness, with values generally near 85% and an estimated 100% for La Hondada. That estimate does not mean every microscopic organism in the water was captured, because completeness is influenced by sampling design, timing, environmental conditions and habitat complexity.

During the rainy season, researchers identified 12 species in Parque de los Cenotes, eight in La Hondada and seven in the fourth cenote, but no species at Cenote Cauich during that period. In the dry season, four species were recorded at Parque de los Cenotes, two each at Cenote Cauich and La Hondada, and one at the fourth site. The seasonal contrast was consistent with the observation of greater protist abundance during the rainy season, especially at Parque de los Cenotes.

Diversity was highest at Parque de los Cenotes, with a reported Shannon-based value of 2.3, followed by La Hondada at 1.7, the fourth cenote at 1.6 and Cenote Cauich at 0.6. Across the sites, the value was 3.2 during the rainy season and 2.5 during the dry season. Rank-abundance curves indicated moderate evenness at La Hondada and Cenote Cauich, high evenness at Parque de los Cenotes and relatively low evenness at the fourth cenote.

No organism dominated all four communities, although Euglena mutabilis, Radiocystis geminata and Aspidisca sp. were prominent at Parque de los Cenotes and Cenote Cauich. Cluster analysis revealed low species similarity among the cenotes, suggesting that each contained a substantial share of taxa not shared with the other sampled sites. The authors related this pattern partly to the broad range of food requirements among protists, while noting that differences in nutrient concentrations, temperature and other physical parameters may also be relevant; however, the study did not directly test which environmental variables produced the community differences.

The scale of the investigation remains a major limitation. It covered four urban cenotes, sampled during two seasonal periods and relied on microscopy and taxonomic keys for identification, so the results should be treated as a snapshot rather than a comprehensive account of all cenotes in Cancun or the wider peninsula. The authors called for systematic monitoring, effective management and conservation, public policies supported by technical and hydrological expertise, and participation by society in protecting these vulnerable freshwater ecosystems.

Subject of Research: Phytoplankton and protist diversity in four urban cenotes in Cancun, Mexico

Article Title: Aquatic microdiversity from urban cenotes in Cancun, Quintana Roo, Mexico

Article References: Díaz-Hernández, J. A., Ugalde-Silva, P., Berriozabal-Islas, C., Novelo, A., Hernández-Uc, J., Arana-May, A., Pech-Patrón, S. D., Nava-Jiménez, I. A., & Borbolla-Vázquez, J. (2023). Aquatic microdiversity from urban cenotes in Cancun, Quintana Roo, Mexico. Subterranean Biology, 46, 129-145. https://doi.org/10.3897/subtbiol.46.108082

Image Credits: AI Generated

DOI: 10.3897/subtbiol.46.108082

Keywords: urban cenotes, Cancun, Yucatán Peninsula, phytoplankton, protist diversity, microbial communities, karst aquifers, seasonal diversity, aquatic microdiversity, water ecosystems, Aquatic, microdiversity

The specimen was captured on 9 December 2024 in Chan Laguna, one of three lagoons that make up the Noh, Chama, and Chan Laguna hydrological system in the municipality of Escárcega, Campeche. A local fisherman caught the fish in a gillnet with a mesh size of 7.62 cm during a research campaign on fish diversity in the Yucatan Peninsula. The researchers immediately recognized it as a Pterygoplichthys specimen, a group of fish easily identified by the bony armor plates covering their bodies and by their distinctive sail-like dorsal fins.

Laboratory examination confirmed the identification. The fish was a male with a total length of 316 mm and a total weight of 280.3 g. It displayed the characteristic leopard-like spots of variable size on its ventral area, a key coloration pattern used to distinguish P. pardalis from related species, along with 11 spines in its dorsal fin. The specimen was deposited in the Ichthyological Collection of the Faculty of Higher Studies Iztacala of the National Autonomous University of Mexico under catalog number CIFI 2401, creating a permanent physical record of the invasion.

Armored catfish of the genus Pterygoplichthys are naturally distributed in southern Central America and South America, where the Amazon sailfin catfish inhabits marginal lagoons and floodplains along the Amazon River and the confluence areas of its main tributaries. The species is one of the most popular in the global aquarium trade, and this commercial popularity is widely believed to be the origin of its global spread. When unwanted aquarium pets are released into local waters, they can establish self-sustaining populations with remarkable ease, thanks to their armor, their ability to breathe air, and their tolerance of poor water quality.

Since 1993, when the species was first recorded in the United States, P. pardalis has been documented across the Caribbean and Central America, including Jamaica, Puerto Rico, Guatemala, the Dominican Republic, and Panama. It has also reached Europe, with records in Serbia, and Asia, where it has been reported in India, the Philippines, Malaysia, Vietnam, Taiwan, Thailand, Indonesia, Israel, Bangladesh, and Sri Lanka. In Mexico, armored catfish have been present since 2003 and are currently found in many regions, including the basins of the Balsas River, the El Infiernillo dam in Michoacán-Guerrero, the Coatzacoalcos, Tonalá, and Papaloapan rivers in Veracruz, the coastal plains of Nayarit and Sinaloa, and especially the Grijalva-Usumacinta system in Chiapas, Tabasco, and Campeche.

Until now, however, no scientific report had documented any Pterygoplichthys species in the Calakmul forest area. The new record is therefore a significant expansion of the known range of this invader into a region of exceptional conservation value. The Calakmul region lies in the southeast of Mexico, in the center of the Yucatan Peninsula, and its western part contains the Noh, Chama-Ha, and Chan Laguna system, also called Silviltuc, Las Maravillas, and Chan Laguna. The Noh Lagoon covers an estimated 6.7 square kilometers, Chama-Ha Lagoon 6.8 square kilometers, and Chan Laguna just 0.45 square kilometers. These lagoons communicate with each other during the rainy season through streams, small ponds, and low-lying swampy areas, and the system is connected to the Candelaria River basin by small streams that reach the Chan Laguna area. The climate is warm subhumid with summer rains, average temperatures between 26 and 28 degrees Celsius, and average total annual rainfall of 1277 mm.

The researchers believe the presence of the species in the area is recent. In sampling campaigns carried out in 2022, there were no reports by fishermen of this type of fish, and previous works in the region do not mention its presence. According to comments from local residents and fishermen, Chan Laguna partially dried up in 2023 and only returned to its previous water levels at the end of 2023 and in 2024, following heavy rains. The two largest lagoons, Noh and Chama-Ha, have not experienced drought events and may serve as reservoirs for local fish fauna, allowing natural repopulation of the smaller lagoon as an adaptation to interannual water fluctuation.

The most likely route of introduction points to the Candelaria River basin. These waters come from nearby parts of the basin, where the presence of Pterygoplichthys was recently reported, although there was already a record of its presence there 10 years earlier. The hydrological connection between the Noh, Chama-Ha, and Chan lagoons and the upper basin of the Candelaria River is temporary, mainly occurring with the flooding of the Tigre and Caribe rivers during the rainy season. Fishermen in the area mention that the first records of this fish in the lagoon were made in that year and that its presence is still scarce. Sampling and interviews with fishermen from the Noh and Chama-Ha lagoons showed that, so far, the fish occurs only in Chan Laguna, and the composition of the catch in the two neighboring lagoons will be monitored.

The effects caused by the presence of armored catfish in the area have not yet been evaluated, but based on previous evidence from other invaded regions, researchers expect serious ecological damage. Documented impacts elsewhere include a decrease in native fish species, a decline in the abundance of submerged aquatic vegetation caused by increased suspended material from the fish’s feeding behavior, changes in nutrient cycles, and increased erosion of shorelines due to the burrows the fish build for nesting. There are also socioeconomic effects, such as damage to fishing gear, particularly gillnets, and injuries to fishermen during the process of removing the spiny fish from nets.

In some areas of Mexico, the consequences have already been severe. At the El Infiernillo dam in Michoacán, armored catfish have caused fishing activity to be abandoned, driven by declining catches of commercial species and rising costs from net losses. The researchers stress that the constant spread of armored catfish in Mexico makes it necessary to carry out studies that analyze and evaluate the factors favoring this expansion, and to implement early warning systems that help control or prevent new areas of Mexico from being invaded. Further research is needed to understand the dispersal pathways of this fish, as well as its potential effects on native fish populations and local fisheries, before the armored invader tightens its grip on one of Mexico’s most important tropical forests.

Subject of Research: Biology

Article Title: First record of armored catfish, Pterygoplichthys pardalis ( Actinopterygii , Siluriformes , Loricariidae ), in the central west area of Calakmul Forest (southern Mexico)

Article References: Wakida-Kusunoki, A. T., Del Moral-Flores, L. F., García-Mercado, E., & Galindo-Hernández, J. H. (2025). First record of armored catfish, Pterygoplichthys pardalis (Actinopterygii, Siluriformes, Loricariidae), in the central west area of Calakmul Forest (southern Mexico). Acta Ichthyologica et Piscatoria, 55, 175-180. https://doi.org/10.3897/aiep.55.151390

Image Credits: AI Generated

DOI: 10.3897/aiep.55.151390

Keywords: invasive species, armored catfish, Pterygoplichthys pardalis, Calakmul, Mexico, Yucatan Peninsula, freshwater fish, biodiversity, aquarium trade, Candelaria River, First, record

The research team, led by Fernando Álvarez of the Universidad Nacional Autónoma de México and colleagues, compiled published carbon and nitrogen isotope data for Typhlatya shrimps from the Yucatan Peninsula and added new measurements from five cenotes. In total, the dataset covered three of the four species present in the region, Typhlatya mitchelli, T. pearsei, and T. dzilamensis, across thirteen cave systems. The fourth Mexican species, T. campecheae, is so rare that no ecological or isotopic data exist for it, so it was excluded from the analysis.

Stable isotope analysis works because the ratio of heavy to light isotopes in an animal’s tissue reflects the food it has consumed. Carbon isotope values, expressed as δ13C, distinguish between different basal food sources: decaying plant material and particulate organic matter typically produce values around -20 to -35 per mil, while biomass from methanotrophic bacteria, which oxidize methane rising from anoxic sediments, yields far more negative values that can reach below -50 per mil. Nitrogen isotope values, δ15N, indicate trophic position, increasing roughly 3 to 4 per mil with each step up the food chain. By reading these signatures, researchers can reconstruct what an animal has been eating without observing it directly.

The results show that Typhlatya shrimps span almost the complete range of δ13C values found in the entire anchialine community, from -22.31 to -55.48 per mil, reflecting the diversity of microbial resources they exploit. The three species showed partially overlapping but distinct carbon ranges. Typhlatya mitchelli had the least negative values, from -22.31 to -39.65 per mil, consistent with feeding on decaying vegetation and bacterial mats dominated by nitrifying bacteria in shallower cave sections. Typhlatya pearsei showed the most negative values, reaching -55.48 per mil, indicating a diet rich in methanotrophic bacteria. Typhlatya dzilamensis fell in between, from -31.26 to -43.78 per mil, likely exploiting resources associated with the halocline, the sharp salinity gradient that traps imported organic material in deeper cave layers.

Statistical comparisons confirmed these differences. A Kruskal-Wallis test revealed significant variation among species, and Dunn’s multiple comparison showed that T. mitchelli differed significantly from T. pearsei and from unidentified Typhlatya individuals. The unidentified specimens from Cenote Bang, reported by Brankovits and colleagues in 2017, showed carbon values between -29.27 and -49.65 per mil, a range consistent with any of the three known species or potentially with a yet undescribed lineage suggested by prior molecular analyses.

To examine how the two dominant freshwater species partition resources, the team constructed convex hulls in δ13C-δ15N space. The hulls for T. mitchelli and T. pearsei overlapped by roughly 20 percent, with T. mitchelli sharing 23.05 percent of its area and T. pearsei sharing 17.62 percent. This limited overlap leaves ample margin for coexistence. Typhlatya pearsei showed broader carbon and nitrogen ranges and a larger total hull area than T. mitchelli, indicating a wider diversity of exploited resources. The overlap zone, at carbon values between -33 and -40 per mil, appears to mark a transition between the two primary feeding strategies.

Seasonal comparisons between the rainy and dry seasons showed no significant differences in carbon isotope values for either species across four cenotes. Paired Wilcoxon signed-rank tests conducted separately for each species and site revealed no seasonal shifts. This stability contrasts with expectations based on prior work showing an inverse relationship between methane concentration and rainfall in an inland cenote of the Ox Bel Ha system. The authors caution that their samples came from geographically distant cenotes collected in 2022 and 2023, whereas the earlier methane study examined a single site during 2015 and 2016, so larger standardized datasets will be needed to determine whether seasonal methane variation consistently affects shrimp isotopic signatures.

Geography mattered. Cenotes in the Ring of Cenotes, an arch of deep, short, unconnected passages around the city of Mérida, showed narrower and less negative carbon ranges for Typhlatya species, averaging -28.65 per mil, than those in the Caribbean Cave Area of Quintana Roo, which averaged -36.20 per mil. The Caribbean Cave Area contains shallower caves with tens to hundreds of kilometers of interconnected passages and strong lateral flows. In this region, organic matter from the overlying rainforest percolates through the rock matrix, generating small amounts of methane that are oxidized by methanotrophic bacteria near cave ceilings. These bacteria provide an additional basal resource that complements direct organic inputs, producing broader carbon ranges consistent with mixed reliance on particulate organic matter and methanotrophic biomass. This process depends on the integrity of the rainforest, which is crucial for maintaining the rich anchialine fauna in remote cave sections where surface organic matter is not transported.

The evolutionary context adds weight to these findings. The family Atyidae is an ancient group of primary freshwater shrimps that probably arose around the Permo-Triassic boundary roughly 250 million years ago. The clade inhabiting anchialine caves may have evolved in late Jurassic or early Cretaceous times, possibly occupying coastal areas of the ancient Tethys Sea. The contemporary distribution of Typhlatya in coastal areas of the Greater Caribbean, Mediterranean Sea, Ascension and Galapagos Islands, and Indian Ocean, along with related genera in Madagascar and Australia, supports this Tethyan origin hypothesis. Fifteen of forty-two atyid genera include cave-dwelling species, a success probably linked to their specialized filter-feeding and scraping mouthparts.

Support for trophic convergence comes from Australia, where Stygiocaris stylifera, a close relative of Typhlatya endemic to the Cape Range Peninsula and Barrow Island, displays isotope values indicative of partial reliance on chemoautotrophic bacterial biomass. This parallel evolution of bacterial-based feeding in distant atyid lineages suggests that the ability to exploit chemoautotrophic production may explain the persistence of anchialine systems as ecological refugia over geological timescales. The versatile feeding apparatus of atyids, with modified first and second pairs of pereopods adapted for scraping rather than cutting, likely facilitates this opportunistic strategy, setting them apart from epigean filter-feeding relatives.

The study’s authors propose that Typhlatya shrimps function as keystone species, introducing nutrients to the anchialine trophic web by taking advantage of microbial production from nitrifying bacteria acting on plant debris and methanotrophic bacteria consuming methane from the water column. Other anchialine species that could feed on bacterial mats, such as the thermosbaenacean Tulumella unidens, occur in numbers too low to play a comparable central role. By converting microbial biomass into animal tissue accessible to predators, Typhlatya shrimps connect primary producers and particulate organic matter with higher trophic levels, potentially facilitating the arrival of other species once they colonize a cave. The breadth of their isotopic niches underscores their trophic importance, the diversity of resources they exploit, and the influence of regional geomorphological differences. Continued study of these shrimps promises to further illuminate the functioning of this still poorly known ecosystem, one of the largest anchialine cave networks on Earth, which may exceed 1,700 kilometers in Quintana Roo alone.

Subject of Research: Stable isotope analysis of trophic niches of Typhlatya cave shrimps in Yucatan anchialine caves

Article Title: The trophic role of cave shrimps of the genus Typhlatya seen through stable isotope eyes

Article References: Durán, B., & Álvarez, F. (2026). The trophic role of cave shrimps of the genus Typhlatya seen through stable isotope eyes. Subterranean Biology, 55, 43-56. https://doi.org/10.3897/subtbiol.55.164068

Image Credits: AI Generated

DOI: 10.3897/subtbiol.55.164068

Keywords: Typhlatya, anchialine caves, stable isotopes, trophic ecology, Yucatan Peninsula, cenotes, methanotrophic bacteria, food webs, Subterranean Biology, isotopic niche, cave shrimps, chemoautotrophy

The research team, led by Daniel Rosas of the Universidad Autónoma de Yucatán together with colleagues from the National Autonomous University of Mexico and Droplet Measurement Technologies, conducted continuous observations in Mérida, Mexico, a near-coastal urban site that sits squarely within the Western Caribbean atmospheric domain. The city, home to more than a million people and one of the fastest-growing metropolitan areas in the country, offers an ideal vantage point for tracking the interplay between long-range transport and local emissions. The researchers combined ground-based measurements of fine and coarse particulate matter, known as PM2.5 and PM10, with continuous monitoring of particle-bound polycyclic aromatic hydrocarbons, a family of toxic organic compounds that cling to soot and other combustion particles and are among the most concerning carcinogens in urban air.

To untangle where the particles came from, the team paired their ground data with satellite-based fire detections from NASA’s FIRMS system and with HYSPLIT back-trajectory simulations, a modeling tool developed by NOAA that reconstructs the path an air parcel traveled before arriving at a measurement site. This combination of observations and trajectory analysis allowed the researchers to link specific pollution episodes to their origins, distinguishing between smoke plumes arriving from fires to the south and dust-laden air masses sweeping in from West Africa. The approach builds on earlier work in the region, including the ADABBOY campaign, which documented African dust and biomass burning over the Yucatán Peninsula, and a long history of studies showing that Saharan dust routinely crosses the entire Atlantic basin to reach the Caribbean and even the Amazon, where it delivers vital nutrients to rainforest soils.

The meteorological backdrop proved to be a decisive actor in the story. During the biomass burning season, the atmosphere over Mérida was dry and turbulent, dominated by southerly flow associated with cold-front intrusions and the dry-season circulation. When the African dust season arrived, conditions flipped: humid easterly trade winds took over, and the boundary layer dynamics changed accordingly. These shifts in wind direction, humidity, and turbulence did not merely accompany the changing aerosol regimes; they actively modulated particle composition at both seasonal and episodic timescales, determining which sources dominated the near-surface air on any given day.

The chemical fingerprints of the two regimes turned out to be strikingly different. During African dust intrusions, total particulate concentrations rose only modestly, but the ratio of PM2.5 to PM10 dropped noticeably. That decline is a classic signature of coarse mineral particles: desert dust grains are relatively large, often several micrometers across, so when they flood into a region they inflate the coarse fraction of the aerosol population while leaving the fine fraction comparatively untouched. Biomass burning, by contrast, produced the opposite pattern. The smoke season was characterized by enhanced fine-mode aerosol contributions, since combustion particles are typically submicron in size, and by episodic spikes in particle-bound PAHs that coincided with intense regional fire activity flagged by satellite sensors. In other words, the two regimes could be told apart not just by how much particulate matter was in the air, but by what kind of particles it contained and when they arrived.

Perhaps the most intriguing finding concerns the daily rhythm of pollution peaks. During the biomass burning season, the highest concentrations of particle-bound PAHs occurred predominantly in the afternoon hours, a timing consistent with regional plume transport, in which smoke generated by distant fires arrives overhead and mixes down to the surface as the day progresses. During the African dust season, by contrast, the peaks clustered in the morning rush-hour window, suggesting a tighter coupling between local traffic emissions and the accumulation of pollutants under early-morning stable conditions. The two regimes, in effect, deliver their pollution burdens at different times of day, through different mechanisms, and from different geographic origins, a distinction that could matter greatly for anyone trying to design effective public health warnings.

When the team translated their measurements into health-risk estimates using benzo[a]pyrene-equivalent concentrations, a standard toxicological approach that weights each PAH compound by its carcinogenic potency, the results were reassuring at first glance. Chronic carcinogenic risk under both seasonal regimes was assessed as low, and the two seasons were statistically indistinguishable in this respect. Benzo[a]pyrene is often used as the reference compound because it is one of the most potent carcinogens among the PAHs, and expressing the total PAH burden in its equivalent terms allows risk assessors to compare exposures across very different chemical mixtures. The finding that neither the smoke season nor the dust season elevates long-term cancer risk above low levels is an important baseline for a region where air quality monitoring has historically been sparse.

But the risk story is more nuanced than a single annual average can convey. The two regimes differed sharply in the magnitude and timing of short-term excursions, the brief episodes when concentrations spike well above their seasonal norms. Biomass burning peaks reached substantially higher concentrations than their dust-season counterparts, meaning that residents of Mérida and surrounding areas experience more intense, if intermittent, exposures to carcinogenic particles during the spring fire season. These acute excursions matter because epidemiological research increasingly suggests that short-term peaks in combustion-derived particulate matter can trigger cardiovascular and respiratory events even when long-term averages appear acceptable. The fact that the two regimes produce peaks at different times of day also implies that exposure mitigation strategies, from timing outdoor activities to scheduling hospital staffing, may need to be tailored to the season rather than applied uniformly year-round.

The broader significance of the study lies in its demonstration that the seasonal duality of biomass burning and African dust exerts a measurable, quantifiable influence on aerosol composition and exposure-relevant indicators across the entire Western Caribbean. Because the two regimes arise from fundamentally different processes, one from fires set and spreading across Central America and southern Mexico, the other from wind erosion in the Sahara followed by transatlantic transport, the appropriate policy responses differ as well. Managing fire-season exposure may require regional coordination on agricultural burning practices, early-warning systems based on satellite fire detection, and public advisories timed to afternoon plume arrivals. Managing dust-season exposure, meanwhile, is largely beyond local control, since the dust originates on another continent, but the morning clustering of peaks suggests that local traffic management and urban planning still have a role to play in limiting total exposure during dust episodes.

For a rapidly growing city like Mérida, perched on the edge of a karstic peninsula where the atmosphere connects the smoke of Central American fires with the dust of the Sahara, the study provides something previous work in the region had not: a season-by-season, hour-by-hour accounting of who is breathing what, and when. As climate change alters fire regimes in the tropics and as dust emissions from North Africa respond to shifting rainfall patterns, the delicate seasonal choreography documented in this research may itself begin to shift. Understanding the baseline, the two alternating regimes and their distinct chemical and temporal signatures, is the essential first step toward detecting those changes and protecting public health as the Western Caribbean’s atmospheric visitors continue their annual rotation.

Subject of Research: Seasonal influence of biomass burning and African dust on aerosol chemistry and particle-bound PAH health risk over the Western Caribbean

Article Title: Biomass burning and African dust influence on seasonal aerosol chemistry over the Western Caribbean (Part I): Atmospheric variability and human health risk from particle-bound PAHs

Article References: Rosas, D., Rodríguez-Gamboa, O. Y., Vega-De-Lille, M. I., Raga, G. B., Baumgardner, D., Ponce-Caballero, C., & Ladino, L. A. (2026). Biomass burning and African dust influence on seasonal aerosol chemistry over the Western Caribbean (Part I): Atmospheric variability and human health risk from particle-bound PAHs. Environmental Science and Pollution Research, 33(28), 14424-14445. https://doi.org/10.1007/s11356-026-38193-x

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38193-x

Keywords: biomass burning, African dust, particle-bound PAHs, PM2.5, PM10, Western Caribbean, Yucatán Peninsula, Mérida, HYSPLIT trajectories, air quality, carcinogenic risk, seasonal aerosol variability

The technique at the heart of speleothem dating, uranium-thorium or 230Th/U dating, relies on a simple principle. When carbonate minerals precipitate from dripping water to form a stalagmite, they incorporate uranium but essentially no thorium. Uranium-234 then decays into thorium-230, so the amount of thorium-230 accumulated in a layer is a direct measure of its age. The method assumes the system remains closed after formation and that no thorium-230 was present at the start. In ideal conditions, age precision depends only on the accuracy of isotope measurements and well-known half-lives. Any deviation — whether from later alteration of the carbonate or from thorium that entered the crystal at the moment of growth — biases the calculated age, typically making samples appear older than they really are.

The trouble is that thorium-230 contamination almost always arrives together with thorium-232, an isotope of purely detrital origin. Geochronologists correct for the initial thorium-230 by assuming a fixed ratio of thorium-230 to thorium-232 in the contaminating material, conventionally a value of about 0.8 derived from average upper continental crust. For clean, old, uranium-rich samples, this correction works well. But in tropical karst systems, studies from Mexico, Belize, Puerto Rico, the Bahamas, Cuba, and the tropical Pacific have reported initial ratios far higher — sometimes tens of times the standard value — and highly variable even within a single cave. When contamination is strong and the assumed ratio is wrong, corrected ages can violate stratigraphy, producing the notorious ‘age inversions’ in which deeper, supposedly older layers date as younger than those above them.

Áaktun Kóopo’ Cave, located in the northeastern Yucatán Peninsula near the communities of La Estrella, Chemax, and Xcan, provided an ideal and demanding test case. The cave extends more than two kilometres through Cretaceous and Tertiary limestones and contains at least nine seasonally fluctuating water bodies. It is also an archaeological site: Maya paintings, polychrome pottery, limestone walls, and the skeletal remains of 23 individuals date to the Late Preclassic and Early Classic periods, with imported flint and obsidian suggesting ritual use by local elites. Between 2018 and 2023, the team collected samples from 15 different speleothems, including ten complete stalagmites between 6.5 and 34 centimetres long, several of which were still actively growing when extracted.

The analytical campaign was exhaustive. A total of 157 samples were dated by high-precision 230Th/U mass spectrometry at Heidelberg University, supplemented by radiocarbon measurements on stalagmite tips to confirm modern growth, X-ray diffraction and thin-section petrography to rule out mineral alteration, laser ablation ICP-MS scans to trace strontium-to-calcium ratios, and stable oxygen and carbon isotope analyses. The uranium concentrations, averaging around one part per million, allowed precise isotope measurements. Yet the results were startling: initial thorium-230 to thorium-232 activity ratios inferred for the cave ranged from 4 to as high as 68, vastly exceeding the standard bulk-earth value of roughly 0.8 and varying unsystematically in both space and time. Modern carbonate and drip water samples yielded elevated ratios of up to about 8.9, but even these did not capture the full range needed to reconcile the dates.

To tame this variability, the researchers deployed three independent approaches. First, they used local ‘isochrons’: closely spaced sub-samples from the same growth layer plot along linear mixing trends between pure carbonate and the detrital contaminant, and the slope of these trends yields a first-order estimate of the initial ratio. Five successful isochrons from three stalagmites produced values between 6.4 and 19. Second, they applied stratigraphic constraints, using samples with no detectable thorium-232 as clean anchors and requiring corrected ages to increase steadily with depth; for one stalagmite, 34 of 51 samples could be ordered this way using individual ratios between 11.5 and 49. Third, they exploited seasonal cycles in strontium-to-calcium ratios, counted with laser ablation scans, as an annual layer chronology. In stalagmite E23-3, 331 distinct minima were counted over 84 millimetres of growth, and aligning the uranium-thorium ages to this count required a ratio of about 26. For samples without specific estimates, the team applied a mean ratio of 35.5 with a large uncertainty of 32.5.

Samples with thorium-230 to thorium-232 activity ratios below 200 — 68 of the 157 dated samples — were excluded from the age models entirely, because for such heavily contaminated material the correction uncertainty swamps any useful chronological information. The remaining 89 samples were fed into six different age-depth modelling algorithms: linear interpolation, linear regression, Bchron, Bacon, COPRA, and StalAge. No single algorithm performed best everywhere; they disagreed notably on the timing and duration of growth interruptions. The team therefore constructed a composite chronology as the arithmetic mean of all successful models, with uncertainty combining both the spread between models and the average within-model uncertainty. The comparison showed that algorithm choice alone can shift the estimated onset of a hiatus by nearly four decades, a sobering illustration of how method-dependent paleoclimate timelines can be.

The validated chronologies reveal continuous carbonate deposition in Áaktun Kóopo’ Cave over the past 2,700 years, with mean growth rates of 200 to 300 micrometres per year, along with evidence of much earlier growth phases during glacial and interglacial periods extending back some 353,000 years. Crucially, the age models could be independently verified. When the stable isotope records of three stalagmites from the same chamber were plotted on their corrected timescales, they showed striking coherence in both oxygen and carbon isotopes, with correlations reaching 0.62 after minor wiggle-matching adjustments that all fell within the calculated 95 percent uncertainty ranges. This replication across independent samples demonstrates that the correction framework produces chronologies robust enough for high-resolution climate reconstruction.

The stalagmites also preserve dramatic evidence of extreme events. A centimetre-thick flooding layer appears in three stalagmites from the same cave area, dated between roughly 1350 and 1430 AD, likely marking a single catastrophic inundation. A sediment record from Cenote Muyil about 80 kilometres south documents intense hurricane activity between 1285 and 1420 AD, and historical sources report a major hurricane — the ‘hurricane of the four winds’ — in 1464 AD, though the exact match remains uncertain. A thinner interruption in two other stalagmites is precisely dated to 1624 AD, plus or minus 24 years. Such event layers, the authors suggest, could serve as stratigraphic tie-points analogous to volcanic ash layers in marine sediments, anchoring proxy records across multiple archives.

Why the thorium ratios vary so wildly remains an open question. The researchers attribute the spread to a shifting mixture of thorium reservoirs in the karst system: detrital clay particles, colloidal phases, and organic complexes mobilized by rapidly dissolving young reef limestone. Because no systematic pattern allows prediction of the initial ratio in advance, the team recommends that future studies in tropical karst combine uranium-thorium dating with radiocarbon, annual layer counting, and stratigraphic constraints rather than relying on any single correction. The payoff is substantial: the corrected Áaktun Kóopo’ records fill a conspicuous gap in high-resolution paleoclimate data from the northeastern Yucatán, where no stalagmite record has covered the last 1,600 years. With reliable timelines now in hand, researchers can begin to disentangle how droughts, floods, and hurricanes intersected with the trajectory of Maya civilization — including the profound upheavals of the Terminal Classic Period around 800 to 1000 AD, when population decline and the abandonment of urban centres reshaped the region.

Subject of Research: Uranium-thorium dating of stalagmites and correction of initial thorium contamination in tropical karst paleoclimate records

Article Title: Challenges of initial Thorium and Approaches to Robust Speleothem Age Models: A case study from the Yucatán peninsula, Mexico

Article References: Schorndorf, N., Warken, S. F., Eichstädter, R., Mielke, A. S., Avilés Olguín, J., Keppler, F., Hennhöfer, D., Tec Pool, F., Evia, C., Gómez, M. J., Stinnesbeck, W., & Frank, N. (2026). Challenges of initial Thorium and Approaches to Robust Speleothem Age Models: A case study from the Yucatán peninsula, Mexico. Geochronology, 8(3), 511-528. https://doi.org/10.5194/gchron-8-511-2026

Image Credits: AI Generated

DOI: 10.5194/gchron-8-511-2026

Keywords: speleothems, uranium-thorium dating, initial thorium, Yucatán Peninsula, paleoclimate, stalagmites, Maya civilization, geochronology, karst hydrology, age-depth models, isochron method, annual layer counting

The story began during a broad survey of the metazoan parasites of marine and estuarine fishes on the Yucatán Peninsula. Between 2023 and 2026, the researchers collected 122 individuals of three sparid fish species: 31 sheepshead, Archosargus probatocephalus; 31 grass porgies, A. rhomboidalis; and 60 pinfish, Lagodon rhomboides. The fish came from two coastal lagoons in the southern Gulf of Mexico, La Carbonera and Celestún, with additional specimens sampled offshore of Celestún. All fish were obtained through commercial capture, dissected, and their gills examined under a stereomicroscope. From these hosts the team recovered dozens of specimens of Lernanthropus, including 21 copepods from sheepshead, two from grass porgy, and 36 from pinfish across the two lagoons, with infection intensities ranging from a single parasite to as many as eleven per infected fish. Specimens were preserved in 100 percent ethanol for both morphological and molecular work, and voucher specimens were deposited in the Colección Nacional de Crustáceos in Mexico City.

Morphologically, the copepods proved a treasure trove of detail that earlier generations of taxonomists had never captured. The females, measured from 14 voucher specimens, range from roughly 2,955 to 5,456 micrometres in total length, with a cephalothorax narrowed anteriorly and a broad, sub-quadrangular trunk bearing a distinctive projection on each side. The well-developed dorsal plate covers only part of the fourth legs, leaving the uropods visible. Among the newly documented traits are the seven-segmented antennules bearing a long aesthete, the subchelate antennae lacking a parabasal flagellum, a mandibular blade armed with seven teeth, and the fine architecture of the maxillules, maxillae and maxillipeds. The team also documented, for the first time in this species, a spermatophore connected to the spermatophore reservoir and onward to the female genital area, a structure essential for sperm transfer that had gone unrecorded in both the original 1922 description and a 2003 redescription from Brazil.

The males, smaller at roughly 1,661 to 1,964 micrometres in total length, received equally thorough treatment. Their antennules are five-segmented and armed with eight setae of varying sizes plus an aesthetasc, while their antennae are bi-segmented with a strongly curved distal claw. The male mandible emerges from within an elongated labrum as a long blade bearing a small tooth, and the fourth legs extend as long as the trunk itself. These appendage-level details matter enormously in copepod taxonomy, because species boundaries within the genus Lernanthropus, which contains 103 described species worldwide, often hinge on subtle differences in the shape and armature of legs, mouthparts and genital structures. By documenting features absent from earlier accounts, the authors have provided the anatomical vocabulary needed for future comparative and phylogenetic studies across the family Lernanthropidae.

On the molecular side, the team extracted total genomic DNA from egg sacs and amplified a partial sequence of the mitochondrial cytochrome c oxidase subunit I gene, the workhorse barcode marker for animal species identification, using the classic Folmer primers LCO1490 and HCO2198. Four isolates of L. caudatus were successfully sequenced, one from sheepshead at 662 base pairs, one from grass porgy at 652 base pairs, and two from pinfish at 629 to 671 base pairs. The new sequences were deposited in GenBank under accession numbers PZ844629 through PZ844632 and compared against published sequences of 18 isolates spanning five genera of the family Lernanthropidae, with the caligid copepod Caligus cybii serving as the outgroup.

The phylogenetic analysis, performed with Maximum Likelihood methods in RAxML on the CIPRES Science Gateway under the best-fitting TIM2 plus I plus G substitution model selected by the Akaike Information Criterion, delivered a clear verdict on species identity. The four isolates of L. caudatus clustered together in a strongly supported monophyletic clade with 99 percent bootstrap support, and their average intraspecific genetic divergence was just one percent. Between L. caudatus and its closest relative in the dataset, L. tylosuri, the genetic distance jumped to 21 percent, and against all other species of Lernanthropus it ranged from 20 to 24 percent. These deep genetic gulfs, far exceeding the shallow within-species variation, confirm that the Yucatán specimens belong to a distinct biological lineage and demonstrate the power of DNA barcoding to anchor century-old morphology-based names in a modern molecular framework.

Not everything in the tree resolved neatly, however, and the authors are candid about the limitations. The cox1 phylogeny showed very low resolution overall and recovered the genus Lernanthropus as paraphyletic, a reflection of how sparse the genetic library remains for this group. Only a fraction of the family’s diversity has been sequenced, and no species of Lernanthropus has yet been characterized for the nuclear ribosomal marker 28S, which the authors recommend as a priority for future work. Interestingly, the related genus Lernanthropinus did emerge as a well-supported clade with moderate nodal support of 86, even though only three of its ten valid species have been sequenced, with interspecific divergences among those three ranging from 14 to 23 percent. The message is clear: without more representative sampling, the evolutionary relationships and classification of these parasites will remain murky.

The redescription also sharpened the diagnostic boundaries between L. caudatus and its closest look-alikes in the wider Caribbean and Gulf of Mexico region. Lernanthropus caudatus can be readily distinguished from L. longilamina, which also parasitizes sheepshead in the Bahamas, by the narrow anterior body region just below the cephalothorax, the shorter dorsal plate relative to body length, and the fourth legs extending beyond the distal margin of the dorsal plate. Against L. amplitergum, known from pinfish in Florida, the differences are equally decisive: L. caudatus has an elongated cephalothorax bearing lobes lateromedially rather than a suborbicular one, a posterior cephalothoracic region that is wider with an anterior projection, and uropods that extend beyond the dorsal plate rather than falling short of it. Such comparisons underscore why exhaustive anatomical documentation remains indispensable even in the genomic era.

Yet the study also revealed meaningful geographic variation within the species itself. Compared with specimens redescribed from Brazil in 2003, the Yucatán animals show a handful of differences: the Brazilian females reportedly possess a fifth leg, which is absent in the Mexican material; the caudal branches are not visible in dorsal view in the Brazilian specimens but are easily observed in the Yucatán ones; the endopod of the second leg lacks a distal spine in Brazil but bears one in Mexico; and the fourth legs are relatively smaller in Brazilian material from red porgy. The authors interpret these discrepancies as intraspecific morphological variability arising from geographic distance and population isolation, noting that while the host fishes extend their range southward to Brazil, the parasite has only been confirmed on a limited set of sparid hosts, and host association combined with isolation may be shaping local morphological divergence.

Beyond its taxonomic significance, the research fills a conspicuous gap in Mexican parasitology. Very few species of Lernanthropus have been reported from Mexican marine waters, with three known from the Pacific coast and only two from the Atlantic seaboard, and no species of the genus had ever been recorded from sparid fish in Mexican waters until now. By uniting classical taxonomy with molecular systematics, the study sets a template for how obscure, long-named parasites can be dragged into the twenty-first century, one gill at a time. As the authors conclude, far more representative sequencing across the Lernanthropidae, ideally including ribosomal markers, will be needed to untangle the true evolutionary tree of this remarkably diverse but poorly sampled lineage of fish parasites.

Subject of Research: Integrative taxonomic redescription and first molecular characterization of the parasitic copepod Lernanthropus caudatus from sparid fishes of the Yucatán Peninsula

Article Title: Redescription and First Molecular Characterization of Lernanthropus caudatus Wilson, 1922 (Copepoda: Lernanthropidae): A Comparative Integrative Analysis

Article References: Espínola-Novelo, J. F., Pérez-Ortega, B. F., Castro-Romero, R., & Pérez-Ponce de León, G. (2026). Redescription and First Molecular Characterization of Lernanthropus caudatus Wilson, 1922 (Copepoda: Lernanthropidae): A Comparative Integrative Analysis. Acta Parasitologica, 71(5), Article 207. https://doi.org/10.1007/s11686-026-01383-1

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01383-1

Keywords: Lernanthropus caudatus, Copepoda, Lernanthropidae, fish parasites, cox1 DNA barcoding, Yucatán Peninsula, sparid fish, morphology, phylogenetics, redescription, Gulf of Mexico, Acta Parasitologica

The research team, led by Diana G. Argaez-Sierra and colleagues at the Universidad Autónoma de Yucatán’s Arbovirology Laboratory, set out to inventory the mosquito fauna of a reserve that had received surprisingly little focused entomological attention despite its ecological prominence. The Ría Celestún Biosphere Reserve is one of the largest of Yucatán’s twelve protected natural areas, encompassing roughly 81,482 hectares of mangroves, coastal dune vegetation, salt marshes, petenes, and lowland floodplain forest on the Gulf of Mexico. The region’s warm, semi-arid climate brings about 767 millimeters of annual rainfall, with relative humidity ranging from 65 to 95 percent and maximum monthly temperatures climbing to 40 degrees Celsius—a combination that creates ideal conditions for mosquito breeding across a mosaic of brackish and freshwater habitats.

Sampling took place during the rainy season in October and November 2024, when the researchers deployed a cross-sectional design across 27 sites representing seven distinct habitat types, including mangrove swamp, salt flats, water surge zones, the bird-nesting islet known as Isla de los Pájaros, coastal scrub, disturbed vegetation, and coastal halophytic vegetation. Working from 19:00 to 22:00 and again from 05:00 to 08:00, the team used two backpack-mounted Prokopack aspirators per night to vacuum adult mosquitoes directly from shaded areas and dense vegetation. They supplemented this active collection with BG-Sentinel traps baited with synthetic human-scent attractant, five traps per site running overnight. Captured insects were immediately preserved in liquid nitrogen and transported to the laboratory, where stereomicroscopes and standard taxonomic keys were used to identify species morphologically.

The results were dominated by a single, familiar face. Of the 3,755 adult mosquitoes captured, females of Aedes taeniorhynchus—the black salt-marsh mosquito—accounted for 95.26 percent of the entire collection and turned up in every habitat sampled. This species is famously associated with coastal wetlands and mangroves throughout the Americas, ovipositing in brackish-water environments and displaying a remarkable tolerance for salinity that few other mosquitoes can match. Its larvae can even colonize artificial containers, allowing the insect to bridge wild and human-modified landscapes. While Ae. taeniorhynchus is primarily a biting nuisance in much of its range, its epidemiological resume is sobering: Venezuelan equine encephalitis virus has been isolated from this species in Guatemala and Costa Rica, eastern equine encephalitis virus in South Carolina, and the Itaqui virus, which causes fever and headache in humans, in Venezuela.

The headline discovery of the survey, however, was Anopheles gabaldoni, a mosquito first described in Tabasco, Mexico in 1941 and subsequently reported in Veracruz and Chiapas, as well as in the neighboring Yucatán Peninsula states of Campeche and Quintana Roo. Its capture in the disturbed vegetation area and on Isla de los Pájaros marks the first record for Yucatán state, raising the state’s documented mosquito tally to 60 species. The identification rests on distinctive abdominal morphology—tufts of posterolateral scales on the tergites and numerous light and dark scales on the sternites—features that the team documented photographically. Intriguingly, all Anopheles species in the study except An. vestitipennis were collected on the islet, including An. albimanus, An. crucians, An. punctipennis, and An. pseudopunctipennis, suggesting that this mangrove-covered bird sanctuary functions as an anopheline hotspot within the reserve.

Habitat type proved to be a strong predictor of mosquito diversity. The disturbed vegetation area yielded the richest assemblage with 12 species, followed by Isla de los Pájaros and the floodable area with seven species each. Although forest modification is generally associated with reduced species diversity, the authors propose that the convergence of disturbed vegetation and highly conserved mangrove may actually amplify mosquito richness by creating edge habitats that satisfy the breeding requirements of multiple species simultaneously. Six of the 27 sampling sites produced no mosquitoes at all, including two sites in the saltworks and three on the islet, underscoring how patchy mosquito distributions can be even within favorable landscapes.

Because morphology alone can mislead—Coquillettidia venezuelensis resembles Cq. nigricans, Anopheles vestitipennis resembles An. neivai, and species of the Aedes subgenus Ochlerotatus are notoriously similar—the team turned to DNA barcoding to confirm the identities of three species. Using the Folmer primers LCO1490 and HC02198, they amplified roughly 700-base-pair fragments of the mitochondrial cytochrome c oxidase subunit I gene. The 704-base-pair COI sequence of An. vestitipennis showed 99.56 percent nucleotide identity with reference sequences in GenBank, and the 687-base-pair sequence of Cq. venezuelensis reached 99.85 percent identity. For Ae. angustivittatus, the 707-base-pair COI sequence showed 98.50 percent identity with a specimen from neighboring Quintana Roo, and a complementary 377-base-pair fragment of the nuclear ITS2 region was also generated. All sequences were deposited in GenBank under accession numbers PZ154394, PZ154395, PZ154396, and PZ158059, adding a permanent molecular reference resource for future mosquito work in the region.

The phylogenetic analysis added a tantalizing evolutionary twist. Bayesian inference conducted in MrBayes, using a 46-sequence dataset of 579 nucleotide positions and Culex quinquefasciatus as an outgroup, revealed that the Celestún Ae. angustivittatus forms a strongly supported lineage with the Quintana Roo specimen, with 98 percent posterior support. But when the researchers calculated pairwise genetic distances, the Yucatán sequences diverged by 3.11 to 4.15 percent from Ae. angustivittatus collected in Chiapas, the State of Mexico, Colombia, and Ecuador. Divergence values in the 3 percent range are often taken as evidence of distinct evolutionary lineages in mosquito DNA barcoding, and the authors suggest that what is currently called Ae. angustivittatus may actually comprise multiple species or distinct subpopulations across its range. They ruled out confusion with the closely related Aedes infirmatus, since interspecific divergence between the two species measured only 2.76 to 2.77 percent, and they note that the ITS2 marker was of limited use here because public databases contain too few ITS2 sequences from closely related Aedes species. Resolving the question will require broader sampling, diagnostic morphological comparisons, and potentially complete mitochondrial genome analysis.

The public health stakes of the inventory are considerable. The Ría Celestún Biosphere Reserve has previously yielded Cache Valley and South River viruses and alphavirus RNA from Ae. taeniorhynchus, alphavirus RNA from An. pseudopunctipennis and An. crucians, and St. Louis encephalitis virus isolated from the bird Cyanocorax yncas. Females of Ae. taeniorhynchus captured at the Mérida zoo tested positive for Cache Valley and Kairi viruses, both of which primarily infect livestock and wildlife but can incidentally infect humans. In Colombian mangrove forests, RNA from St. Louis encephalitis, yellow fever, dengue, Venezuelan equine encephalitis, and West Nile viruses has been detected in mosquitoes, and Venezuelan equine encephalitis virus and St. Louis encephalitis virus have been found in Mansonia titillans—one of the eight species newly recorded at Celestún. With the reserve attracting heavy tourism and hosting dense communities of birds and mammals, the presence of competent vector species creates precisely the ecological conditions under which zoonotic arboviruses can circulate undetected until they spill over into human populations.

Methodologically, the study also delivered a practical lesson for surveillance design: the backpack aspirator captured 94.70 percent of all mosquitoes across 15 species, while the BG-Sentinel traps, which excel at collecting human-biting species like Ae. aegypti, accounted for just 5.30 percent across nine species. For rare species such as Ae. angustivittatus, An. vestitipennis, Cq. venezuelensis, and Ma. titillans, both methods contributed in similar proportions, suggesting that combining techniques remains essential for a complete picture of diversity. The authors are candid about the limitations of a single wet-season pass through the reserve; each site was inspected only once, and dry-season sampling will be needed to capture seasonal shifts in species composition. They also call for intensified arbovirus testing on Isla de los Pájaros, whose hundreds of nesting pelicans, herons, frigatebirds, and cormorants make it a natural laboratory for understanding how mosquitoes, birds, and viruses interact in one of the Yucatán’s most ecologically vital corners. With 24 species now documented across the reserve—40 percent of Yucatán state’s entire mosquito fauna—Celestún has firmly established itself as a frontier for entomological discovery on Mexico’s Gulf coast.

Subject of Research: Mosquito species inventory and DNA barcoding in a Mexican mangrove biosphere reserve

Article Title: Mosquito fauna (Diptera: Culicidae) in the Ria Celestún Biosphere Reserve (RCBR) with a new record for Yucatán, México

Article References: Argaez-Sierra, D. G., Cigarroa-Toledo, N., Baak-Baak, C. M., Tzuc-Dzul, J. C., Cetina-Trejo, R. C., Talavera-Aguilar, L. G., Chi-Chim, W. A., Arana-Guardia, R., & García-Rejón, J. E. (2026). Mosquito fauna (Diptera: Culicidae) in the Ria Celestún Biosphere Reserve (RCBR) with a new record for Yucatán, México. Discover Animals, 3(1), Article 93. https://doi.org/10.1007/s44338-026-00253-4

Image Credits: AI Generated

DOI: 10.1007/s44338-026-00253-4

Keywords: mosquitoes, Culicidae, Anopheles gabaldoni, Ría Celestún Biosphere Reserve, Yucatán, DNA barcoding, COI gene, arboviruses, Aedes taeniorhynchus, mangroves, biodiversity, vector surveillance

The urgency of the work is grounded in real events. At Xocén, the roof of an underground cavern gave way suddenly in the middle of a Maya community, toppling a two-century-old Ceiba tree and opening a sinkhole roughly 57 meters in diameter and up to 36 meters deep. The researchers believe intense rainfall and the passage of heavy construction machinery in the days before the collapse triggered the failure of a cavern ceiling that had been weakening for a long time below the surface. At Saamal, an open cenote popular with visitors, partial collapse of the steep cliff walls suggests that even mature, apparently stable karst features can remain structurally active for years.

The scientific setting is extraordinary. The Yucatán’s cenote density traces back to the Chicxulub impact crater, the roughly 200-kilometer-wide scar left by the asteroid that ended the Cretaceous period. The crater’s fractured rim created a zone of enhanced permeability, the so-called Ring of Cenotes, along which carbonate dissolution concentrated over millions of years. When acidified rainwater percolates through limestone, it enlarges fractures and voids until the remaining roof can no longer support its own weight. Because karst terrains show few visible warning signs at the surface until failure occurs, they account for a disproportionate share of sudden ground-collapse hazards worldwide.

Conventional geotechnical investigation relies on drilling and excavation, methods that are expensive, slow, and impractical to deploy across many sites immediately after a collapse. ERT offers an alternative. By injecting electrical current into the ground through arrays of electrodes and measuring the resulting voltage differences, the technique produces cross-sectional images of subsurface resistivity. Competent dry limestone appears highly resistive, while water-saturated, clay-rich, or heavily weathered rock conducts electricity well. Air-filled voids also register as strong resistive anomalies. These contrasts map directly onto the mechanical properties that govern collapse susceptibility.

At Xocén, the team deployed a Syscal Pro system with Wenner and Schlumberger electrode arrays along three profiles totaling up to 110 meters each, reaching effective investigation depths of roughly 16 to 25 meters. After filtering unreliable readings and inverting the data with a smoothness-constrained least-squares algorithm, the final models achieved root-mean-square misfits between about 2 and 2.5 percent. The inverted sections revealed a consistent vertical stratification: a resistive cap of dry limestone more than 1000 ohm-meters, an intermediate transition zone of partially weathered rock, and a laterally continuous conductive interval below 250 ohm-meters interpreted as water-saturated, highly altered limestone, whose top approximates the local water table.

Most striking was a vertically persistent conductive anomaly in one profile, where resistivity dropped below 150 ohm-meters, linking the surface to the deep conductive layer. The researchers interpret this feature as a fracture-controlled infiltration corridor, a preferential pathway through which water percolates, accelerating dissolution and progressively weakening the rock mass. This geometry suggests that the Xocén collapse was not an isolated surface event but the geomorphological expression of a pre-existing weakened subsurface domain, with future instability most likely concentrated at the interfaces between the resistive cap, the transition zone, and the deeper conductive material.

At Saamal, five closely spaced profiles were acquired along the vulnerable cliff rim using a SuperSting R8 system, with electrodes just one meter apart to resolve the approximately 3-meter-thick limestone ledge involved in the recent failures. A robust, blocky inversion captured the sharp contrasts near the wall. The sections showed a thin weathered conductive veneer half a meter to a meter thick overlying competent carbonate rock, plus a very high-resistivity domain exceeding 1600 ohm-meters adjacent to the cliff, interpreted conservatively as a dry, possibly fractured carbonate block. Because air-filled cavities and dry rock yield similarly high resistivities, the authors caution that resistivity magnitude alone cannot confirm open voids. To visualize domain continuity between profiles, the team trained a neural network to interpolate the independently inverted two-dimensional sections into a three-dimensional resistivity volume, a supporting tool rather than a true 3D inversion.

A depth-of-investigation analysis following the established Oldenburg and Li method confirmed that the models are constrained by real data to mean depths of about 19.7 meters at Xocén and 2.9 meters at Saamal, guarding against over-interpretation of poorly resolved regions. The authors are candid about limitations: no borehole, geotechnical, or piezometric control was available, so the inferred domains remain hydrogeophysical rather than directly verified, and the resistivity thresholds are site-specific rather than universal. They recommend corroboration through fracture mapping, ground-penetrating radar, shallow seismic surveys, and repeat ERT monitoring after rainfall events.

The broader significance lies in translating geophysical images into operational disaster-risk decisions. The study proposes that collapse-prone sectors be identified not by a single universal signature but by site-specific combinations of shallow weathered conductive veneers, laterally connected saturated zones, fracture-controlled infiltration pathways, and sharp resistivity interfaces. Classifying ground into high, intermediate, and low susceptibility zones gives authorities a defensible basis for restricting access, prioritizing monitoring, and planning land use around cenotes in populated or heavily visited areas. As reported collapses of cenote roofs increase across the Yucatán, this rapid, affordable screening framework offers communities and tourism operators a practical first line of defense against one of nature’s most sudden geological traps.

Subject of Research: Electrical resistivity tomography screening of collapse susceptibility in karst cenote environments of the Yucatán Peninsula, Mexico

Article Title: Electrical Resistivity Tomography for collapse susceptibility screening in karst cenote environments: A case study in the Yucatán Peninsula, Mexico

Article References: Juárez, S. L., Alemán, J. C. O., Castañeda, C. C., Hernandez, J. F. E., Perez, D. A. P., & Martinez, J. M. (2026). Electrical Resistivity Tomography for collapse susceptibility screening in karst cenote environments: A case study in the Yucatán Peninsula, Mexico. Environmental Challenges, 25, Article 101642. https://doi.org/10.1016/j.envc.2026.101642

Image Credits: AI Generated

DOI: 10.1016/j.envc.2026.101642

Keywords: cenotes, karst, electrical resistivity tomography, Yucatán Peninsula, sinkhole collapse, Chicxulub crater, geophysics, Xocén, Saamal, disaster risk, limestone dissolution, Ring of Cenotes