Where fresh and marine waters meet, chemical and biological stratification generates reservoirs of biodiversity with high endemism, housing specialized communities such as stygobiont crustaceans and fish adapted to low light and low oxygen. Yet while copepods, remipedes, ostracods, amphipods, and cave fish have been documented in detail, the sponges of Phylum Porifera have remained almost entirely unexplored for over five decades. The historical record is thin.

In 1936, Old documented Spongilla lacustris and Ephydatia crateriformis — now recognized as Radiospongilla crateriformis — in Yucatan cenotes. In 1968, Penney and Racek described a new species, Spongilla cenota, from a different cenote. Poirrier later confirmed that the material identified as S. lacustris was actually S. cenota, so all specimens of S. lacustris in Yucatan cenotes were reassigned.

Since then, the biodiversity of freshwater sponges in these ecosystems has remained largely unexplored, with only two species ever reported. To close this gap, researchers led SCUBA surveys in two open-type cenotes. Sabak-Ha, in the municipality of Sacalum, is 60 meters long and 30 meters wide with a recorded depth of 120 meters — though its true depth is unknown.

From the surface to about 15 meters, a layer of organic matter creates extremely low visibility, and it is here, attached to the walls, that the sponges were found. No sponges were detected in the crystal-clear waters below. Suhem, in the municipality of Pixya, ranges from 4 to around 35 meters deep and is a popular tourist site.

Specimens were deposited in the Colección Nacional del Phylum Porifera – Gerardo Green at UNAM's Instituto de Ciencias del Mar y Limnología. The sponges displayed remarkable plasticity. In Sabak-Ha, they formed massive encrusting structures with prominent mounded and discoidal growth forms, appearing greenish-yellow in illuminated areas and dull pinkish in shaded zones — a color shift likely linked to photosynthetic symbionts.

In Suhem, they were diminutive, attenuated, and irregularly encrusting. The skeleton consists of paucispicular tracts of 2 to 5 intersecting oxea spicules forming an alveolate structure with rounded meshes, with generally scarce but present spongin. Under light and scanning electron microscopy, the spicule architecture told a precise story.

Smooth oxeas occurred in two size categories: the dominant type I measured 327.13 micrometers on average (243.28–373.53 micrometers), while the shorter, thinner type II averaged 172.55 micrometers. Spiny oxeas, found exclusively in one Sabak-Ha specimen, averaged 110.71 micrometers. Gemmuloscleres consisted of birotules with spined shafts and rotules of nearly identical morphology at both extremities, averaging 46.76 micrometers in length with rotule diameters of 23.41 micrometers.

Gemmules, observed only in Suhem specimens, were hemispherical and measured about 200.56 micrometers in diameter. Molecular analysis sealed the identification. DNA was extracted from ethanol-preserved samples and amplified with primers targeting the ITS1, 5.8S, and ITS2 regions plus partial 18S and 28S sequences.

BLAST searches against GenBank revealed that sequences from both cenotes were identical in nucleotide composition and differed by less than 3 percent from reference sequences of E. fluviatilis. Phylogenetic reconstruction using Maximum Likelihood and Bayesian Inference yielded congruent topologies, placing the cenote sponges in a well-supported monophyletic clade with E. fluviatilis, sister to clades of Heterorotula and Racekiela. Sequences are deposited in GenBank under accession numbers PX492551, PX492552, and PX492553.

Notably, the birotules from Sabak-Ha were longer (44.65–72.96 micrometers) than the typical range for E. fluviatilis (26–30 micrometers), while those from Suhem fell closer to the expected range (32.66–43.15 micrometers). This interpopulation variation suggests that site-specific environmental conditions within each cenote influence spicule formation and growth. Spine development on birotule shafts has been linked to elevated chloride concentrations and high alkalinity — conditions characteristic of cenote ecosystems — indicating that the spination reflects environmentally induced variation rather than species-level diagnostic characters.

With this discovery, the number of known cenote sponge species has risen to three, each from a different genus, and two new cenotes have been added to existing records, bringing the total to six cenote ecosystems with freshwater sponge populations. Given the high number of cenotes across the Yucatan Peninsula, further undiscovered species are likely. Notably, most of the cenotes where sponges have been reported lie outside the Reserva Estatal Geohidrológica Anillo de Cenotes, a Natural Protected Area established in 2013.

The study underscores the importance of integrating molecular and morphological data for accurate species identification, particularly in a genus where species delimitation has historically relied on the presence or absence of spines. Freshwater sponge research can illuminate water chemistry, illustrate the evolutionary history of ecosystems, and offer resources for biotechnological applications. As sponges have been overlooked in cenote biodiversity inventories for over 40 years, fundamental aspects of their ecology and biology in these unique karst environments remain unknown — creating valuable opportunities for future research into the environmental conditions that determine sponge presence, their spatiotemporal distribution across the cenote network, and their associated microbiomes.

Subject of Research: Discovery of the freshwater sponge Ephydatia fluviatilis in Yucatan cenote ecosystems using morphological and molecular analyses

Article Title: New discovery of the freshwater sponge Ephydatia fluviatilis (Linnaeus, 1759) in cenote ecosystems of Yucatan, Mexico: Morphological and molecular insights

Article References: Hernández-Solis, P. A., Gómez-Bretón, V. E., de la Cruz-Fernández, D. A., & Simões, N. (2026). New discovery of the freshwater sponge Ephydatia fluviatilis (Linnaeus, 1759) in cenote ecosystems of Yucatan, Mexico: Morphological and molecular insights. Subterranean Biology, 55, 109-136. https://doi.org/10.3897/subtbiol.55.177524

Image Credits: AI Generated

DOI: 10.3897/subtbiol.55.177524

Keywords: freshwater sponges, cenotes, Yucatan, Ephydatia fluviatilis, karst ecosystems, Porifera, taxonomy, DNA barcoding, Subterranean Biology, Mexico biodiversity, discovery, freshwater

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 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