Anurans, the order that includes frogs and toads, are famously sensitive vertebrates. Their permeable skin demands moisture, their life cycles are tightly coupled to both aquatic and terrestrial conditions, and their distributions are strongly shaped by environmental stability. Yet these same vulnerabilities make caves attractive. Natural subterranean environments offer high and relatively stable humidity, reduced temperature fluctuations, and near-total darkness, conditions that shield amphibians from desiccation and from visually oriented predators. Caves frequently host abundant invertebrate prey and often contain watercourses suitable for reproduction, making them potential all-purpose shelters for animals that are predominantly nocturnal to begin with.

To understand which anurans actually exploit these environments, the researchers compiled 177 occurrence records covering 54 species from the scientific literature, drawing on Google Scholar, Scopus, and the Web of Science following PRISMA guidelines for systematic searches. Only records with complete species-level identification were retained, and nomenclature was verified against the authoritative Amphibian Species of the World database. Each species was then characterized by its conservation status under both the IUCN Red List and the Brazilian Ministry of the Environment, its geographic distribution, endemism, and a suite of life-history traits including activity period, body size, habitat, and breeding site.

The statistical centerpiece of the study was a redundancy analysis, a multivariate technique that relates a matrix of explanatory variables to a matrix of response variables. Before running the model, the team checked for multicollinearity among predictors using variance inflation factors, keeping all variables below the conventional threshold of 10.0. The analysis revealed that three variables tied to conservation status and geography, namely IUCN status, distribution area, and endemism, best explain which anurans turn up in Brazilian caves. These three predictors accounted for 27.0 percent of the total variance explained by the model, with the first two ordination axes capturing 31.1 percent of the variance, and the overall model was statistically significant at p = 0.001.

The dominance of Least Concern species was striking. Of all occurrence records compiled, 94.3 percent corresponded to species classified as Least Concern under both the IUCN and the Brazilian national list. Threatened categories were marginal by comparison: Vulnerable species made up 3.5 percent of IUCN-classified records and Endangered species 1.5 percent, while the national classification included Near Threatened at 3.5 percent and Endangered at 1.5 percent, with 0.7 percent of records not evaluated. Eight species were strongly associated with the conservation-status variable, including the poison frog Adelphobates galactonotus, the rocket frog Allobates marchesianus, the striped poison frog Ameerega flavopicta, several hylid tree frogs of the genera Boana and Bokermannohyla, and the cycloramphid Cycloramphus eleutherodactylus. Only one species, Bokermannohyla martinsi, carried a Vulnerable designation.

Why would common, wide-ranging species dominate cave records? The authors argue that broad geographic distributions signal low niche specificity. Species capable of occupying heterogeneous environments, from leaf litter to stream margins to rock crevices, possess the ecological plasticity to treat caves as one more available microhabitat. Ameerega flavopicta, Cycloramphus eleutherodactylus, and Boana boans, for example, already use rock crevices, holes in slopes, tree trunks, and bromeliad rosettes, microhabitats whose microclimatic conditions resemble those inside caves. Such surface habits provide indirect evidence that these animals can tolerate, and potentially exploit, subterranean conditions when the need arises.

Geographic distribution and endemism carved the species into three distinct biogeographic patterns. Scinax ruber and Scinax x-signatus are non-endemic and widely distributed, hylid tree frogs that thrive in everything from anthropized open areas to preserved forest interiors, a versatility that favors opportunistic cave occupation as temporary shelter. Thoropa miliaris and Thoropa taophora are endemic but relatively widespread within their regions, often associated with disturbed or heterogeneous environments, and may enter caves seasonally during periods of surface water or thermal stress. Finally, Thoropa megatympanum stands apart as endemic with a restricted range, confined to the rupestrian landscapes of the Serra do Espinhaço in Minas Gerais. Its presence in caves appears less tied to generalism and more to the availability of humid rocky microhabitats, since the genus deposits eggs on wet surfaces and its tadpoles are adapted to water films on rock, demanding high humidity stability.

Perhaps the most counterintuitive finding was what did not matter. Life-history variables, including activity period, body size, habitat, habits, and breeding site, contributed little to the model’s explained variance and were not selected as determinants of cave presence. The authors suggest this reflects both ecological reality and methodological limitations: life-history traits for many Neotropical anurans are incompletely or inconsistently reported, weakening their statistical power. The result implies that cave occupation depends less on physiological or behavioral specialization and more on the geographic and ecological context of each species, reinforcing the interpretation of caves as complementary microhabitats open to a broad range of ecologically distinct species.

The study also exposes a regulatory blind spot. Under Brazilian environmental legislation governing subterranean environments, anurans are classified as accidental fauna, a category for animals that wander into caves without the capacity to sustain themselves there. Because of this designation, there is no legal obligation to record or collect anurans during cave studies, in contrast to bats, fish, and invertebrates, which are explicitly covered and have driven much subterranean research since Federal Decree 6640 in 2008. This legal gap has left herpetofauna marginal in biospeleological research, producing sporadic records and regional sampling biases that the authors caution should temper interpretation of macroecological patterns drawn from published data.

The implications for conservation are concrete. The researchers recommend systematically incorporating anuran surveys into environmental licensing procedures and speleological inventories, since these animals are currently overlooked in many cave monitoring programs. They also point to emerging tools, acoustic monitoring, environmental DNA detection, and genetic comparisons between cave and surface populations, as promising avenues for clarifying habitat use, detectability, and population connectivity in subterranean ecosystems. For now, the message is clear: Brazilian caves are not frog fortresses of rare endemics but flexible refuges serving the generalists, and protecting them means recognizing that even common species depend on the stability these dark chambers provide.

Subject of Research: Macroecology of anuran habitat use in Brazilian caves

Article Title: Opportunistic habitat use: widespread and non-threatened anurans in Brazilian caves

Article References: Sperandei, V. D. F., Vaz-Silva, W., Pereira, C. C., & Tejerina-Garro, F. L. (2026). Opportunistic habitat use: widespread and non-threatened anurans in Brazilian caves. Neotropical Biology and Conservation, 21(1), 31-48. https://doi.org/10.3897/neotropical.21.e184592

Image Credits: AI Generated

DOI: 10.3897/neotropical.21.e184592

Keywords: anurans, Brazilian caves, cave ecology, amphibians, redundancy analysis, IUCN conservation status, endemism, ecological plasticity, Neotropical biodiversity, subterranean habitats, trogloxenes, systematic review

The research team, led by Ling Su of the Jiangxi Academy of Eco-Environmental Sciences and Planning, monitored twenty sampling sites across the reservoir’s Jinkou and Sima areas every month from May 2022 to April 2023. Their goal was to fill a conspicuous gap in freshwater ecology: while shallow, nutrient-polluted lakes in China have been studied extensively, deep reservoirs with complex thermal layering, engineered water-level swings, and steep underwater terrain remain poorly documented. Lushan West Reservoir, with a storage capacity of 7.92 billion cubic meters, an average depth of 18.59 meters, and a maximum depth of 45 meters, offered an ideal natural laboratory.

What the team found was a community of remarkable richness and volatility. In total, 116 phytoplankton species belonging to eight phyla were identified. Green algae of the phylum Chlorophyta led in sheer species count, accounting for 43.97 percent of the catalog, followed by diatoms of Bacillariophyta at 28.45 percent and cyanobacteria at 17.24 percent. Yet species richness told only part of the story. When it came to actual abundance, cyanobacteria dominated throughout the year, making up between 48.64 and 62.26 percent of cells in spring and surging to as much as 94.72 percent in winter.

The seasonal rhythm of total cell density was equally striking. Numbers peaked at 9.98 million cells per liter in September, crashed to roughly 1.72 million cells per liter by December, and bottomed out below one million cells per liter in the early spring months of February and April. A curious dip occurred in June, when density plummeted from 7.86 million to 1.08 million cells per liter. The researchers attribute this collapse to pre-flood dam operations, which flush water through the reservoir, shorten the time phytoplankton spend in productive zones, and dilute populations before they can recover.

To untangle which environmental variables were steering these shifts, the team employed redundancy analysis, a multivariate statistical technique suited to linear species-environment relationships. The model explained 62.4 percent of the total variation in community structure, with the first two ordination axes accounting for 57.5 percent. Four factors emerged as the principal drivers: water temperature, transparency, total nitrogen, and total phosphorus. Transparency carried the strongest conditional effect, followed closely by temperature, both statistically significant at the one percent level.

The thresholds the study identified read like an ecological rulebook. When water temperature climbed above 25 degrees Celsius, total phosphorus reached 0.22 milligrams per liter, and total nitrogen hit 1.29 milligrams per liter, cyanobacterial biomass peaked at 0.42 milligrams per liter and cell density hit its annual maximum. Conversely, when temperatures fell below 13 degrees Celsius and transparency exceeded 320 centimeters, diatom relative abundance climbed to 41.80 percent. These numbers align with the reservoir’s own seasonal extremes: summer water temperatures reached 28.42 degrees Celsius, while winter lows dipped to 12.68 degrees.

One of the study’s most intriguing findings concerns a seeming paradox. Total phosphorus showed no statistically significant seasonal variation when measured in integrated water-column samples, yet cyanobacterial dominance fluctuated dramatically with the seasons. The authors resolve this by pointing to thermal stratification. In summer, a stable thermocline forms in the deep reservoir, creating oxygen-poor conditions in the bottom layer that trigger the release of phosphorus from sediments. This internally loaded phosphorus accumulates below the thermocline and cannot fully mix into surface waters, which is why whole-column measurements miss it. But bioavailable dissolved phosphorus diffuses upward into the sunlit zone, where warm temperatures supercharge cyanobacteria’s phosphorus uptake efficiency, giving them a decisive competitive edge.

Niche analysis added a competitive dimension to the picture. Using Levins’ modified niche breadth index, the researchers found that diatoms maintained relatively broad ecological niches, with values ranging from 1.75 to 2.54, reflecting their ability to exploit a wide range of conditions. Cyanobacteria, however, achieved even wider niche widths, from 1.25 to 2.78, with the filamentous species Pseudanabaena sp. topping the scale at 2.78. This broad adaptation, combined with efficient resource utilization, explains how cyanobacteria sustain year-round dominance despite seasonal environmental swings. Green algae, by contrast, occupied narrower niches between 0.40 and 1.58, limiting their competitive reach.

The study also carries a sobering management message. Pollution source census data cited in the paper reveal that urban domestic wastewater is the dominant external nutrient source, contributing 936.15 tons of total nitrogen and 51.33 tons of total phosphorus annually to the watershed. Industrial discharges add another 44.43 tons of nitrogen and 1.11 tons of phosphorus per year. The authors recommend prioritizing sewage collection and treatment upgrades, agricultural buffer strips, riparian restoration, and controls on tourism-related discharges to curb the external nutrient inputs that fuel summer cyanobacterial blooms.

For a reservoir that serves as both a drinking water source and a scenic tourism destination, the stakes are considerable. Cyanobacterial blooms can release toxins, suppress zooplankton communities, and disrupt energy flow through the food web, while diatom dominance tends to stabilize primary productivity and aid nutrient recycling through the deposition of siliceous shells. By pinpointing the temperature and nutrient thresholds at which the balance tips, this research offers water managers a quantifiable early-warning framework, not just for Lushan West Reservoir but for the many deep, regulated reservoirs scattered across the mountainous landscapes of southern China.

Subject of Research: Seasonal dynamics of phytoplankton community structure and environmental drivers in a deep freshwater reservoir

Article Title: Spatiotemporal dynamics of phytoplankton community structure in freshwater reservoir and its relationship with environmental factors

Article References: Su, L., Li, L., Ji, Y., Xiong, P., Cheng, W., Wan, F., & Liu, H. (2026). Spatiotemporal dynamics of phytoplankton community structure in freshwater reservoir and its relationship with environmental factors. Frontiers in Water, 8, Article 1906226. https://doi.org/10.3389/frwa.2026.1906226

Image Credits: AI Generated

DOI: 10.3389/frwa.2026.1906226

Keywords: phytoplankton, cyanobacteria, diatoms, freshwater reservoir, eutrophication, water quality, thermal stratification, niche analysis, redundancy analysis, total phosphorus, total nitrogen, China

Phytoplankton, the drifting microscopic organisms that form the base of aquatic food webs, are often described as sentinels of environmental change. Because they respond rapidly to shifts in temperature, light, and nutrient availability, their community composition can reveal the hidden fingerprints of hydroclimatic stress long before those fingerprints appear in water chemistry alone. In reservoirs that supply drinking water to growing populations, this sensitivity is both a gift and a threat: the same conditions that reshuffle phytoplankton communities can open the door to blooms of nuisance or toxic species, degrading water quality and driving up treatment costs. Yet North African reservoirs, despite their enormous socio-economic importance in a region where water scarcity is escalating, remain strikingly underrepresented in the functional ecology literature. The new study set out to close that gap by asking how a functionally organized algal community behaves under the kind of hydroclimatic variability that is becoming the Mediterranean norm.

The research team, led by Soumya Saidi of the Laboratory of Dynamics and Biodiversity at USTHB in Algiers, together with colleagues from the École Normale Supérieure in Kouba, sampled the reservoir monthly at four stations across two complete hydrological years. Their methodology combined classical taxonomic identification with the Reynolds functional group classification, a framework that sorts phytoplankton not by evolutionary lineage but by shared morphological and physiological traits that determine where and when particular species thrive. On top of this trait-based classification they layered the Phytoplankton Assemblage Index, known as the Q index, which scores ecological status based on the sensitivity of dominant assemblages to environmental conditions. Diversity metrics captured the breadth of the community, while redundancy analysis, a multivariate statistical technique, was used to link patterns in functional group composition to the physical and chemical conditions measured in the water column.

The sheer taxonomic wealth documented over the two years was remarkable. A total of 165 taxa, distributed across 76 genera and 10 algal classes, were identified in the reservoir. Species richness did not remain steady through the seasons; it swung between a low of 25 taxa in autumn 2023 and a high of 66 taxa in winter 2024, a fivefold oscillation that mirrors the seasonal pulse of the Mediterranean climate, where cool, wet winters give way to hot, desiccating summers. Biovolume, a measure of the total volume of living algal cells per liter of water, told an equally dramatic story. Phytoplankton biovolume peaked above 150 cubic millimeters per liter in spring 2023, then declined steadily to roughly 30 cubic millimeters per liter by spring 2025, an approximately fivefold drop across two years that the researchers attribute to interannual variability in nutrient availability and other physicochemical conditions within the reservoir.

Beneath that fluctuating surface of taxonomic richness, however, lay a community that was strikingly uniform in its functional architecture. Although 24 functional codons were recorded over the study period, the community was overwhelmingly dominated by a single codon, L0, whose flagship species is Ceratium hirundinella, a large armored dinoflagellate with distinctive horn-like projections. This one group consistently accounted for between 60 and 71 percent of total biovolume throughout the sampling campaign. The persistence of codon L0 at such dominance reveals something important about how the reservoir works: the environmental filters operating in Boukourdane, including thermal stratification during warm months and episodic mixing during cooler periods, appear to consistently favor large, mixotrophic dinoflagellates capable of exploiting both photosynthesis and the consumption of other microbes when nutrients run short. Ceratium hirundinella is a classic species of stable, stratified water columns, and its ability to regulate buoyancy and harvest resources across a range of conditions allows it to persist when smaller, faster-growing algae are starved out.

The Q index, which translates functional group identity into an ecological quality score, ranged from 2.18 to 2.89 across the study, values that correspond to a moderate ecological status throughout the two hydrological years. That plateau is significant for water resource managers because it suggests that, despite substantial swings in biovolume and species richness, the reservoir’s ecological condition remained stable rather than deteriorating or recovering during the study window. Moderate status in a drinking water reservoir is not a crisis, but neither is it comfort: it indicates that the system sits in a sensitive middle zone where shifts in nutrient loading or climate forcing could push it either toward improvement or toward the eutrophic conditions that fuel harmful algal blooms. Given that intense lake phytoplankton blooms have been increasing globally since the 1980s, and that Mediterranean water bodies face compounding pressures from warming, drought, and abstraction, the moderate status of Boukourdane should be read as a call for vigilance rather than reassurance.

The statistical heart of the study came from redundancy analysis, which disentangled the environmental variables most tightly coupled to the functional structure of the phytoplankton community. The analysis explained 62.5 percent of the constrained functional variance, a remarkably high figure in ecological research where stochastic processes and unmeasured variables often obscure clear relationships, and the result was statistically significant at p equal to 0.001. Three environmental filters emerged as the dominant orchestrators of community structure: thermal stratification, alkalinity, and dissolved inorganic nitrogen. Thermal stratification, the layering of warm surface water over cooler deep water that develops in summer, shapes which functional groups can persist by controlling access to light and nutrients. Alkalinity, which reflects the water’s buffering capacity and carbonate chemistry, constrains which species are physiologically comfortable in the reservoir. Dissolved inorganic nitrogen, the plant-available form of a key nutrient, governs how much biomass the community can build in any given season. Together, these three variables act as a nested set of gates through which only certain functional strategies can pass.

The implications of this environmental control extend well beyond the boundaries of the Boukourdane catchment. As hydroclimatic variability intensifies across the Mediterranean basin, prolonged drought cycles like the one that struck the reservoir in 2021 will increasingly concentrate nutrients, extend stratification periods, and alter the delivery of nitrogen and other elements from shrinking catchments. The study’s finding that interannual changes in biovolume reflect temporal variability in nutrient availability suggests that the algal community of the reservoir acts as an integrating recorder of upstream hydrological conditions. When drought reduces inflows and concentrates solutes, the phytoplankton respond; when wetter years flush the system with fresh nutrients, the community shifts again. Reading those responses through a functional lens, rather than a purely taxonomic one, gives water managers a diagnostic tool that is more robust than species counts alone, because functional groups remain interpretable even as species identities vary across regions and seasons.

What makes the study especially valuable is its demonstration that the functional group framework, combining Reynolds codons, the Q index, and multivariate ordination, can serve as an effective early warning architecture in a data-poor region. North African water managers often lack the long-term monitoring infrastructure available in Western Europe, and the ability to derive meaningful ecological intelligence from monthly sampling at a handful of stations is a practical advantage. The dominance of codon L0 and its Ceratium hirundinella flagship provides a clear baseline against which future change can be measured: if cyanobacterial codons begin to displace the dinoflagellate during warm, nutrient-enriched periods, that transition would signal a shift toward bloom-prone conditions demanding immediate management response. Conversely, continued stability in the L0 dominance pattern would suggest that the reservoir’s environmental filters remain within their historical envelope. The research team, which also included Siham Arab, Nour El Houda Malki, and Somia Hamil, has provided a template that can be replicated in other Mediterranean and North African reservoirs, transforming scattered monitoring efforts into a coherent, comparable network capable of tracking how the region’s most vital water infrastructure is coping with a climate that is increasingly unwilling to cooperate.

Subject of Research: Phytoplankton community structure and functional dynamics in a Mediterranean drinking water reservoir under hydroclimatic variability

Article Title: Phytoplankton community structure and functional dynamics in a Mediterranean reservoir under hydroclimatic variability

Article References: Saidi, S., Arab, S., Malki, N. E. H., & Hamil, S. (2026). Phytoplankton community structure and functional dynamics in a Mediterranean reservoir under hydroclimatic variability. Environmental Monitoring and Assessment, 198(10), Article 1066. https://doi.org/10.1007/s10661-026-15920-y

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15920-y

Keywords: phytoplankton, functional groups, Mediterranean reservoir, hydroclimatic variability, Ceratium hirundinella, Q Assemblage Index, redundancy analysis, thermal stratification, drought, Algeria, water quality, ecological monitoring