Shell morphology in intertidal gastropods reflects environmental conditions, especially hydrodynamic forces and substrate characteristics. We investigated shell shape variation in the commercially exploited grazer Phorcus sauciatus across contrasting coastal orientations, North versus East, and substrate types, natural versus artificial, in Gran Canaria. A total of 378 specimens were collected from exposed and sheltered environments, including rocky platforms, large rocks, and artificial structures such as breakwaters and seawalls. Geometric morphometrics, using anatomical landmarks and outline curves, together with size-standardised shell measurements, showed that coastal orientation was the main driver of morphological variation. Northern groups had lower, more horizontally elongated shells consistent with high wave exposure, whereas eastern groups showed taller, more globose shells associated with sheltered conditions. Substrate type modulated local-scale shape differences. Platform-associated groups showed the highest morphological disparity, suggesting greater within-group morphological dispersion, while artificial substrates and rock habitats showed lower variability and more restricted morphospace occupancy. Discriminant and canonical variate analyses provided moderate cross-validated classification accuracy, indicating partial separation and substantial overlap among groups. These results show that shell morphometrics can detect environmentally associated shape variation and provide a complementary tool for spatial monitoring and management of data-limited intertidal fisheries.
Shallow coastal bays and lagoons are important habitats supporting high biodiversity and many charophyte species. Charophyte habitats are particularly vulnerable to anthropogenic activity and restoring them has become a current management issue. To investigate the environmental requirements needed for charophyte site restorations, we tested how sediment characteristics affect the survival and growth of the key species Chara tomentosa. As C. tomentosa predominantly occurs in sheltered areas with organic muddy sediment, we hypothesised that sandier sediments would reduce its survival and growth. In aquaria, apical cuttings were planted in natural organic-rich sediment with three levels of sand addition (0, 40, and 80 vol
We investigated the influence of seasonality and the phycoperiphyton on the colonization dynamics of zooperiphyton on artificial polyethylene terephthalate substrates in a tropical hypereutrophic reservoir. We tested the hypothesis that seasonal climatic conditions drive changes in zooperiphyton colonization and successional trajectories, with stronger effects on functional aspects of the community. In situ colonization studies lasting 28 days were conducted during two seasons. Substrates were sampled, and associated phycoperiphyton and zooperiphyton communities were identified and quantified, while environmental variables were measured to characterize the environment. Structural equation models were used to determine the effects of the phycoperiphyton on zooperiphyton. The zooperiphyton assemblage was composed of rotifers, ciliates, testate amoebae, insects, and nematodes. Rotifers exhibited the highest species richness, while ciliates dominated the community structure throughout both seasons. Epistylis plicatilis was the primary colonizer after 3 h in both seasons. Successional processes progressed more rapidly during the dry season, likely due to more stable, favorable abiotic conditions. In the rainy season, high rainfall and stalked algae influenced the zooperiphyton community. Furthermore, prostrate, stalked, and entangled algae influenced herbivores and predators. Our findings demonstrate that seasonal disturbances, such as rainfall, mediate the interactions between phycoperiphyton and zooperiphyton, thereby shaping the biofilm’s successional trajectory.
Mangrove sediments sequester large amounts of carbon, yet local controls on sediment organic carbon (SOC) remain uncertain. We tested how rainfall variability and dominant mangrove species relate to sediment physicochemical conditions and intertidal crab assemblages in five Eastern Pacific mangrove forests (Colombian Pacific coast). Sampling was conducted during the higher and lower rainfall periods in forests dominated by Rhizophora mangle or Avicennia germinans. We quantified crab density, assemblage composition, and burrow characteristics. We also measured sediment temperature, pH, conductivity, texture, bulk density, and SOC to 50 cm depth. We found a crossed response to rainfall: sediment properties differed most strongly between rainfall periods in A. germinans forests, whereas crab assemblages responded more clearly in R. mangle forests. Canonical correspondence analysis showed statistically significant but modest associations between crab assemblages and sediment variables; the reduced model explained only 14.1
Excessive anthropogenic inputs of nitrogen and phosphorus into surface waters remain a major challenge for river ecosystem management, with wastewater treatment plants (WWTPs) representing key point sources of nutrients, particularly in densely populated regions. In this study, we investigated the effects of nutrient loads from WWTPs of different sizes (i.e. small, medium, and large) on macroinvertebrate communities across the Po River District (Northern Italy). Using basin-scale nutrient load estimates and macroinvertebrate metrics derived from Water Framework Directive, we assessed taxonomic, functional, and trait-based response to nitrogen and phosphorus loads. Results showed that large and small WWTPs contributed the greatest nutrient loads, and that these loads were significantly associated with shifts in community structure and functional diversity. High nutrient loads favoured tolerant taxa, reduced diversity of sensitive groups, and promoted trait modalities linked to enriched and depositional habitats. Responses of functional traits were particularly pronounced for small WWTPs, indicating strong ecological effects despite their limited size. Our findings underscore the need to integrate load-based approaches into regulatory frameworks, moving beyond concentration-based standards to capture cumulative nutrient pressures, especially under increasing hydrological intermittence and water scarcity in river networks.
Neotropical freshwater biodiversity is remarkable, mainly due to historical, biotic, and environmental processes. Landscape connectivity can promote or restrict species dispersal in fish metacommunities, thereby influencing the diversity and phylogenetic structure of communities. This study evaluated whether structural landscape variables of the Tramandaí River basin affect the phylogenetic diversity of the component communities of a fish metacommunity. The variables considered were primary and estuarine connection, lake shape and area, and distance from the sea. Phylogenetic diversity was estimated using a time-calibrated fish phylogeny and multiple phylogenetic diversity metrics, while the relationships between landscape variables and each metric were assessed using path analysis. The distribution of phylogenetic lineages across lakes was examined using Principal Coordinates of Phylogenetic Structure. The results revealed a negative effect of primary connection on the Nearest Relative Index and a negative effect of distance from the sea on the Nearest Taxon Index, as well as phylogenetic structuring associated with more isolated lakes and greater saline influence. The results highlight the importance of connectivity and distance from the sea in shaping the phylogenetic organization of fish metacommunities in the Tramandaí River basin, contributing to a better understanding of the processes that structure diversity in Neotropical coastal systems.
Kelp holdfasts form dense 3D habitat that supports diverse biological communities, but the relative importance of different structural components and the methods used to measure them are poorly understood. Here, we compare multiple 3D imaging approaches spanning different levels of cost and accessibility including CT scanning, photogrammetry and depth sensing, to quantify the structural complexity of holdfasts in the kelp Ecklonia maxima (Osbeck) Papenfuss. Furthermore, we link the taxonomic and functional diversity of both macrofaunal and macroalgal holdfast assemblages to specific structural metrics. Blender interstitial volume was positively associated with macrofaunal abundance and taxonomic richness, but negatively associated with functional evenness. Conversely, haptera density was positively associated with taxonomic diversity and evenness, as well as functional distance and divergence. The macroalgal assemblages responded primarily to the availability and quality of interstitial volume. These contrasting responses demonstrate that habitat complexity is multidimensional, with different components governing taxonomic and functional diversity. Accordingly, the ecological relevance of structural metrics is context dependent, highlighting the need to align measurement approaches with research questions or employ complementary metrics. By advancing both conceptual and methodological understanding, this study quantifies habitat complexity to better predict biodiversity and functional responses related to environmental change and habitat homogenisation.
The benthic rotifer Euchlanis dilatata produces Rotimer, a filamentous biopolymer forming persistent three-dimensional webs on substrate surfaces. Rotimer is conserved across Rotifera and serves basal functions in females, but its function in non-feeding, short-lived males remains unclear. We test whether female-produced Rotimer functions as a mate-search cue detectable by males. We propose the Benthic Rotifer Encounter Model (BREM), extending planktonic encounter theory to substrate-anchored systems by substituting the Rotimer web’s effective encounter radius for the female body radius; BREM is bidirectional in principle, though only the female-to-male direction was tested here. Consistent with BREM, female webs were structurally more complex than male webs, and males showed greater trajectory straightness in the presence of female Rotimer. Directed tracking of conspecific Rotimer to copulation was observed in both sexes. These findings support BREM’s female–male encounter pathway and generate testable predictions for mate-search dynamics in benthic microinvertebrates.
Understanding the functional roles of species is invaluable to conservation planning and effective ecosystem management. We used stable isotope analyses to examine the functional role of two primary burrowing crayfishes from the Piedmont region of South Carolina, USA, across both roadside and field habitats. Distocambarus youngineri served as a secondary consumer in roadside and field habitats, with similar trophic positions between habitats, sex, and size. Distocambarus youngineri relied heavily on primary and secondary consumers, with invertebrates contributing up to 82
Freshwater ecosystems are exposed to altered hydrological regimes due to climate change and poor water management, resulting in frequent and intense dewatering events. Freshwater mussels (Unionida) are particularly vulnerable to rapid water-level declines. Dewatering can lead to mortality through stranding and desiccation, yet inter- and intra-specific variation in responses is rarely assessed, in Europe, limiting conservation planning. We evaluated dewatering effects on three European freshwater mussel species (Unio delphinus, U. elongatulus, and U. pictorum), each represented by northern and southern populations. Mussels were exposed to slow, moderate, and fast dewatering rates and a control. Horizontal movement, burrowing, and strandedness (i.e. mussels completely emersed showing no response to external stimuli for a minimum of 1 h) were quantified. Horizontal movement did not differ from controls, although the northern population of U. pictorum showed decreased movement under fast dewatering. Burrowing varied among species and populations, with only the northern population of U. pictorum exhibiting significant differences in the fast dewatering treatment compared to the control group. Strandedness differed significantly among species, treatments, and populations, with U. elongatulus most affected overall. Our results reveal context-dependent behavioural responses to dewatering, highlighting the need to incorporate population-level variability into freshwater mussel conservation and flow management strategies.
Phytoplankton effective quantum yield of Photosystem II (Fv’/Fm’) is a sensitive indicator of aquatic ecosystem health, yet it remains underutilized in tropical freshwaters. We evaluated the diurnal and seasonal variations of Fv’/Fm’ and its relationship with Morphology-Based Functional Groups (MBFGs) in a hypereutrophic tropical urban pond over 15 months. In situ measurements of Fv’/Fm’ (without dark acclimation) and limnological parameters were recorded five times daily, alongside phytoplankton community sampling. Fv’/Fm’ values were consistently low throughout the study, indicating chronic physiological stress. Linear mixed-effects models and redundancy analysis identified electrical conductivity and photosynthetically active radiation (PAR) as the primary negative drivers of physiological efficiency and major determinants of community structure. Seasonal hydrological shifts, rather than short-term diurnal variations, dictated community dynamics. Small organisms (Group I) dominated the dry season under high PAR, whereas large bloom-forming cyanobacteria (Groups VII/VIII) and flagellates (Group V) dominated the rainy season, driven by elevated conductivity. These findings establish active fluorescence as a robust, real-time monitoring tool for tropical freshwaters, demonstrating that chronic environmental stressors, particularly electrical conductivity, overshadow traditional factors in shaping the physiological limits and functional structure of phytoplankton assemblages.
Over recent decades, Iceland has experienced a decline in conventional agriculture, a rapid increase in tourism and significant climatic change, all of which can potentially influence lake ecosystems. To investigate limnological changes over the past 70 years, sediment cores were collected from two lakes: Hafravatn, near Reykjavík and surrounded by summerhouses, and Grænavatn, a less accessible lake 25 km south-west of Reykjavík. Analyses of chironomid head capsules and geochemical parameters reveal that Hafravatn is well-buffered against increasing human activities and changing climate, possibly due to its larger surface area (c. 1.01 km2) and depth (c. 28 m). Short-lived shifts in chironomid assemblages coincide with changes in sediment accumulation rate, associated with infrastructure projects. However, no significant correlation was found between the chironomid assemblage and the number of summerhouses present. The chironomid assemblage of Grænavatn shows long-term shifts mainly caused by changes in summer temperatures, which likely influence lake-water levels and habitat availability. Due to Grænavatn’s smaller and shallower basin (c. 0.62 km2, c. 4.4 m) or lack of other influences, the chironomid assemblage likely responded more sensitively to climate change. This study shows that lake size and bathymetry are important determinants of resilience to land-use and climate change in Iceland.
Zooplankton and phytoplankton produce resting stages that enable populations to persist through adverse conditions. Between 2019 and 2022, the Paraná River in South America experienced historical drought leading to the desiccation of floodplain lakes. To evaluate the resilience of plankton communities under such conditions, we experimentally assessed the emergence of zooplankton and phytoplankton from resting stages in 13 temporary shallow lakes of the Lower Paraná floodplain varying in lake hydroperiod (i.e., water permanence). We determined species richness and composition and assessed the time to zooplankton first hatching. We compared the composition of emerged plankton with the corresponding active assemblages recorded in the lakes. The species richness in assemblages recruited from the sediments was lower than in the active communities and decreased with increasing lake water permanence. The dissimilarity between emerged and active assemblages increased with lake permanence. The time until the first zooplankton hatching lengthened with greater water permanence. Our results demonstrate a negative effect of extreme droughts on the recovery of plankton communities from resting stages and highlight the key role of lake hydroperiod as a modulator of resting bank responses to drought. This study provides insights into the consequences of more frequent and prolonged droughts for floodplain plankton communities.
Neotropical cichlids are characterized by spectacular color diversity, but some groups remain poorly investigated. In this context, the present study characterized color traits in peacock basses (Cichla kelberi and C. piquiti) from the Middle Tocantins River (Brazil), and investigated the link with biological (development, sex, reproduction) and environmental drivers (feeding and water transparency). Both species showed striking polychromatism, but with some conspicuous patterns. For C. kelberi, immature and non-reproductive individuals were associated with melanistic patterns and the absence of spots, with either conspicuous or opaque vertical bars. Adults in reproduction, on the other hand, were associated with yellow body, spots in the fins, and dorsal blotches. For C. piquiti, immature and non-reproductive individuals showed a wide range of color patterns, but associated with non-blue tints. Immature fish, in particular, had spots in the body and head, and a red caudal fin. Reproductive fish were associated with blue hues, the absence of spots and a non-red caudal lobe. For both species, color variation was not associated with feeding, sex and water transparency. Our findings indicate that coloration represents transient (but stable) phenotypic states subjected to unidirectional or cyclical changes, supporting the hypothesis that growth and reproduction drive color variation in Cichla.
Biodiversity assessments often rely on taxonomic diversity (TD), which may fail to capture evolutionary and ecological dimensions represented by phylogenetic (PD) and functional diversity (FD). This study evaluates the spatial congruence and partial decoupling of these facets in Heroini cichlids across Middle American watersheds. Using species occurrence data, a multilocus phylogeny, and ecological traits, we characterized alpha- and beta-diversity and assessed their spatial relationships. At local scales, alpha-diversity facets were highly correlated, with hotspots concentrated in the Grijalva–Usumacinta and San Juan basins. While taxonomic and phylogenetic diversity showed high spatial congruence, lower overlap with functional diversity suggested functional redundancy in species-rich assemblages. In contrast, beta-diversity facets exhibited partial decoupling. Taxonomic and phylogenetic turnover displayed similar spatial patterns, whereas functional turnover was more heterogeneous and weakly associated with the other facets. These patterns likely reflect the combined influence of historical biogeography, including colonization via GAARlandia, and ecological specialization leading to functional convergence. Overall, biodiversity patterns were strongly scale-dependent, with different facets following partially independent spatial trajectories. These findings highlight the importance of multifaceted and multiscale approaches for identifying and conserving priority freshwater systems in Middle America while accounting for complementary evolutionary and functional dimensions of biodiversity.
Accurate information on the current extent and ecological condition of ponds is essential for effective conservation planning and implementation. However, such efforts are often limited by insufficient or outdated mapping. The use of remote sensing using satellites offers a potential mapping tool for these small features. This paper uses a case study from south-west England to assess the feasibility of using remote sensing to identify ponds examining the full remote sensing workflow including image availability, satellite sensor selection, costs and detection performance across multiple sensors and methods. Detection improved with increasing spatial resolution, with higher spatial resolution imagery enabling smaller ponds to be identified under optimal conditions but this incurred higher costs. However, across all methods, performance was limited by high rates of false positives and omission errors. Precision was consistently low, indicating that many detected ponds were not true ponds, while the proportion of real ponds correctly detected varied depending on the sensor and method used. Pond size, relative to satellite sensor pixel size, was the most influential factor in detectability and misclassification, with the presence of macrophytes also playing a key role. This research provides the first comprehensive assessment of the remote sensing workflow for pond detection in the UK and offers broader insights into identifying small landscape features. The findings support conservation and research efforts and serve as a practical guide for others seeking to apply these techniques in similar contexts.
Warming and eutrophication can alter the structure of aquatic communities. In shallow lakes, zooplankton associated with submerged macrophytes exhibit high species richness and play a key role in maintaining clear-water conditions and enhancing water quality. However, their responses to warming and eutrophication remain poorly understood. We conducted a 65-day mesocosm experiment to evaluate the effects of temperature (ambient vs. warmed), nutrient concentration (oligotrophic vs. eutrophic), and substrate type (natural vs. artificial macrophytes) on the richness, density, biomass, and mean body size of the zooplankton community associated with Egeria densa. Temperature negatively affected density but positively affected mean community body size, likely reflecting shifts in species dominance under warming, despite reductions in body size at the individual species level. In natural macrophytes, temperature influenced species richness under eutrophic conditions, whereas in artificial macrophytes, temperature effects on richness were observed under oligotrophic conditions. These results demonstrate that warming and eutrophication can strongly modify the structure of the zooplankton communities associated with macrophytes. Such sensitivity suggests that, under ongoing climate change, the capacity of these communities to contribute to the maintenance of clear water may be substantially reduced.
The hyperdiverse Neotropical fish fauna is spatially distributed in a core-periphery pattern, with species richness and endemism highest in the core (i.e. western Amazon, Orinoco, Guianas hydrographic basins), richness-controlled endemism highest in the periphery (all other basins), and faunal differentiation congruent with basins. However, given marked body-size differences between the most speciose fish taxa and Neotropical freshwater stingrays (NFS), the core-periphery hypothesis may not apply to NFS. Additionally, continental-scale freshwater diversity patterns are commonly analysed using basin or ecoregion polygons of irregular shape and size, preventing within-basin analyses. Here, we infer continental-, basin-, and river-scale patterns of NFS diversity using longitudinal extents of occurrence which, after rasterisation, allowed a finer-grained analysis than irregular polygons. At continental scale, NFS diversity was better explained by river size than by the core-periphery arrangement. At basin scale, the importance of river size or the core-periphery pattern depended on the basin. At river scale, a near mid-river peak in species richness was observed. Finally, NFS-defined bioregions were highly congruent with basins. These scale-dependent patterns would have been impossible to unveil, had we used irregular polygons as sample units. These methods can be applied to any taxon depending exclusively on rivers to disperse (e.g. fishes, bivalves).
Macrobrachium amazonicum is a widely distributed freshwater prawn inhabiting river basins across South America. It includes both diadromous and hololimnetic populations, exhibiting notable differences in bioecological, physiological, and reproductive traits. Individuals from the Pantanal region display distinct characteristics that led to their classification as a separate species, Macrobrachium pantanalense. Despite these differences, studies using mitochondrial markers (COI and 16S rRNA) have revealed low genetic divergence, identifying three distinct genetic lineages. This study analyzes multiple mitochondrial genomes from M. amazonicum and M. pantanalense populations, based on transcriptome-derived data, to improve understanding of evolutionary relationships and genetic structure within the “Macrobrachium amazonicum complex”. Mitogenome coverage ranged from 51.6 to 63.1
Small constructed waterbodies (CWs) are common in agriculturalized landscapes worldwide, but their potential influence on stream fish assemblages is understudied. We hypothesized constructed waterbodies in (impoundments) and adjacent (artificial ponds) to streams were associated with changes in fish communities across the Black River basin over a 30- to 40-year period. We investigated relationships between increases of fishes commonly stocked in CWs for recreation, stream fish community change variables, and CW-intensity variables at three spatial scales (watershed, reach, and 1 km radius). Using satellite imagery in Google Earth® Pro, we quantified variables for 2559 CWs across 56 sites. Artificial ponds were distinguished from impoundments as occurring outside of the perennial stream network. Pond intensity (increased pond number and area) was positively correlated with percent tolerant individuals in contemporary collections and negatively correlated with community stability, 1 – Bray–Curtis dissimilarity between historical and contemporary assemblages. Pond intensity had stronger, more consistent relationships with community-level variables across spatial scales than impoundment intensity. Thresholds at which pond densities can shift fish community structure were identified with TITAN2. Our data support that, not only impoundments, but adjacent ponds may act as sources for translocation of native stocked species into streams leading to alterations of stream fish communities.
