Permanent Ponds Research Articles

Blowing in the wind: how many roads can a phytoplanktont walk down? A synthesis on phytoplankton biogeography and spatial processes

The selected theme of the 17th Workshop of the International Association for Phytoplankton Taxonomy and Ecology (IAP), “Biogeography and Spatial Patterns of Biodiversity of Freshwater Phytoplankton,” offered the opportunity to explore one neglected aspect of phytoplankton ecology: the distribution of species in the geographic space. This paper summarizes the outcomes of 20 selected contributions among those presented at the workshop. The articles report the results from studies carried out in five continents (only Oceania is not represented) and on a wide array of aquatic ecosystems (deep and shallow natural lakes, man-made lakes, temporary and permanent ponds, rivers). The topics analyzed by the contributors are related to Island Biogeography paradigms, dispersal vectors, survival strategies, environmental filters, dispersal distances, vertical and horizontal spatial variability of phytoplankton between and within water bodies, and of course, invasive algae. The overall analysis of the results presented clearly demonstrates that, as for many others organisms, there are “rules” governing freshwater phytoplankton spatial patterns and that these organisms also have a true biogeography, as nowadays is quite evident for several other groups in the same range of size. We can definitively conclude that the statement “Everything is everywhere” is obsolete, even though human activities tend to homogenize species distribution in the biosphere.

Life history differences influence the impacts of drought on two pond-breeding salamanders.

Drought is a strong density-independent environmental filter that contributes to population regulation and other ecological processes. Not all species respond similarly to drought, and the overall impacts can vary depending on life histories. Such differences can necessitate management strategies that incorporate information on individual species to maximize conservation success. We report the effects of a short-term drought on occupancy and reproductive success of two pond-breeding salamanders that differ in breeding phenology (fall vs. spring breeder) across an active military base landscape in Missouri, USA: We surveyed ~200 ponds for the presence of eggs, larvae, and metamorphs from 2011 to 2013. This period coincided with before, during, and after a severe drought that occurred in 2012. The two species showed contrasting responses to drought, where high reproductive failure (34% of ponds) was observed for the spring breeder during a single drought year. Alternatively, the fall breeder only showed a cumulative 8% failure over two years. The number of breeding ponds available for use in the fall decreased during the drought due to pond drying and/or a lack of re-filling. Estimates of occupancy probability declined for the fall-breeding salamander between 2012 and 2013, whereas occupancy probability estimates of the spring breeder increased post-drought. The presence of fish, hydroperiod, the amount of forest cover surrounding ponds, and canopy cover were all found to affect estimates of occupancy probabilities of each species. Pond clustering (distance to nearest pond and the number of ponds within close proximity), hydroperiod, forest cover, and canopy cover influenced both estimates of colonization and extinction probabilities. Our results show life history variation can be important in determining the relative susceptibility of a species to drought conditions, and that sympatric species experiencing the same environmental conditions can respond differently. Consideration of the spatial network and configuration of habitat patches that act as refuges under extreme environmental conditions will improve conservation efforts, such as the placement of permanent ponds for aquatic organisms. A better awareness of species-specific tolerances to environmental filters such as drought can lead to improved management recommendations to conserve and promote habitat for a greater diversity of species across landscapes of spatially connected populations.

Modeling the dynamics of mosquito breeding sites vs rainfall in Barkedji area, Senegal

Mosquito-borne diseases like Rift Valley Fever and Malaria that cause serious health threat to human and livestock populations are known to correlate with the tremendous increase of associated mosquito vectors following periods of widespread and heavy rainfall. In the Barkedji area, Senegal, rainfall occur only during the July–October wet season, and mosquito breeding sites are provided by relatively small temporary ponds, which account for the vast majority of the water surfaces during the rainy season. Given that rain fed ponds play a key role in the epidemiology of the mosquito-borne diseases, we have developed an approach allowing to model the flooding/drying dynamics of rain fed ponds in the Barkedji area by combining the detection of ponds using optical remote sensing techniques, field data on a small set of monitored ponds and modeling of both the pond profile, shapes and the flooding/drying dynamics at the single-pond level for each pond in the entire region.As a result, we have computed on output the daily flooding/drying dynamics for each of the 1345 rain fed ponds detected in Barkedji area as a function of the daily rainfall in input. As dry and fluctuating ponds are less productive in mosquitoes, the ponds are characterizes in terms of flooding-drying fluctuations and of resistance to dryness by computing the total number of time per year a pond dries out and the pond lifetime, respectively. And, clusters of ponds with identical behavior, i.e., clusters of temporary, semi-permanent and permanent ponds, were subsequently identified.As a perspective, we show how this work can be used for modelling mosquito population dynamics and addressing the issues of associated impacts of climate change.

Exotic Fish in Exotic Plantations: A Multi-Scale Approach to Understand Amphibian Occurrence in the Mediterranean Region.

Globally, amphibian populations are threatened by a diverse range of factors including habitat destruction and alteration. Forestry practices have been linked with low diversity and abundance of amphibians. The effect of exotic Eucalyptus spp. plantations on amphibian communities has been studied in a number of biodiversity hotspots, but little is known of its impact in the Mediterranean region. Here, we identify the environmental factors influencing the presence of six species of amphibians (the Caudata Pleurodeles waltl, Salamandra salamandra, Lissotriton boscai, Triturus marmoratus and the anurans Pelobates cultripes and Hyla arborea/meridionalis) occupying 88 ponds. The study was conducted in a Mediterranean landscape dominated by eucalypt plantations alternated with traditional use (agricultural, montados and native forest) at three different scales: local (pond), intermediate (400 metres radius buffer) and broad (1000 metres radius buffer). Using the Akaike Information Criterion for small samples (AICc), we selected the top-ranked models for estimating the probability of occurrence of each species at each spatial scale separately and across all three spatial scales, using a combination of covariates from the different magnitudes. Models with a combination of covariates at the different spatial scales had a stronger support than those at individual scales. The presence of predatory fish in a pond had a strong effect on Caudata presence. Permanent ponds were selected by Hyla arborea/meridionalis over temporary ponds. Species occurrence was not increased by a higher density of streams, but the density of ponds impacted negatively on Lissotriton boscai. The proximity of ponds occupied by their conspecifics had a positive effect on the occurrence of Lissotriton boscai and Pleurodeles waltl. Eucalypt plantations had a negative effect on the occurrence of the newt Lissotriton boscai and anurans Hyla arborea/meridionalis, but had a positive effect on the presence of Salamandra salamandra, while no effect on any of the other species was detected. In conclusion, eucalypts had limited effects on the amphibian community at the intermediate and broad scales, but predatory fish had a major impact when considering all the scales combined. The over-riding importance of introduced fish as a negative impact suggests that forest managers should prevent new fish introductions and eradicate fish from already-occupied ponds whenever possible.

Relative performance of ecological niche and occupancy models for predicting invasions by patchily-distributed species

Ecological niche models (ENM) have been used with mixed success for predicting the geographic extent of non-native species to aid management and conservation. This approach is problematic for predicting invasions of patchily-distributed species (e.g., pond-breeding amphibians), whose occurrence is often determined by local habitat conditions. Here, we tested the performance of bioclimatic ENM for predicting occurrence (from repeated surveys) of two non-native pond-breeding anurans at 71 wetlands in British Columbia, Canada: permanent pond specialist American bullfrog (Lithobates catesbeianus), and generalist green frog (Lithobates clamitans). For L. catesbeianus, we assessed the risk of invasion beyond the invasion front. We found higher correlation between ENM and occupancy predictions for L. clamitans (r s = 0.58), than for L. catesbeianus (r s = −0.26). L. clamitans occurrence was highest at low elevations and high annual precipitation; in contrast, L. catesbeianus occupancy was predicted by wetland connectivity and distance from a historic introduction site [low at isolated ponds >50 km from the introduction site, and high (>0.8) at all ponds with >10 % water within 500 m]. Conditional on successful dispersal, four sites beyond the L. catesbeianus invasion front surveyed in this study were at high risk of invasion due to high habitat suitability (proportion of area occupied = 0.33; 0.04–0.83, 95 % CI). In conclusion, ENMs may be useful for informing invasion management for climate driven wetland species, but repeated sampling is necessary to predict invasions for habitat-driven wetland species.

Pond macroinvertebrates of the Presidential Estate of Castelporziano (Rome): a review of ecological aspects and selecting indicator taxa for conservation

Macroinvertebrates of 49 (27 temporary and 22 permanent) ponds located in the Presidential Estate of Castelporziano (Rome) were studied from 1989 to 2004 to investigate their community ecology and to provide a first estimation of their conservation value. More than 300 taxa (about 70 % identified to species) were collected. The main environmental factors influencing the number of species in the study ponds were hydroperiod length, depth, surface area, dissolved oxygen concentration and macrophyte species richness and abundances. Permanent biotopes generally hosted higher number of taxa than temporary ones. Some taxa were exclusive or more abundant in a pond type. Functional organization (functional feeding groups, habits and resistance to desiccation) of the community appeared similar in the two pond types but differed among mesohabitats. Up to date, about 62 % of the taxa collected have an unknown status with respect to their distribution in Italy (common, rare, threatened and vulnerable). We identified 50 target species with peculiar ecological requirements and/or geographical distribution to promote effective practical basis for pond conservation in Italy. The distribution of rare, vulnerable or threatened species within the ponds studied suggests that the two pond types and all mesohabitats therein should be considered for the sampling procedure to obtain a correct evaluation of pond conservation.

Intermediate pond sizes contain the highest density, richness, and diversity of pond-breeding amphibians.

We present data on amphibian density, species richness, and diversity from a 7140-ha area consisting of 200 ponds in the Midwestern U.S. that represents most of the possible lentic aquatic breeding habitats common in this region. Our study includes all possible breeding sites with natural and anthropogenic disturbance processes that can be missing from studies where sampling intensity is low, sample area is small, or partial disturbance gradients are sampled. We tested whether pond area was a significant predictor of density, species richness, and diversity of amphibians and if values peaked at intermediate pond areas. We found that in all cases a quadratic model fit our data significantly better than a linear model. Because small ponds have a high probability of pond drying and large ponds have a high probability of fish colonization and accumulation of invertebrate predators, drying and predation may be two mechanisms driving the peak of density and diversity towards intermediate values of pond size. We also found that not all intermediate sized ponds produced many larvae; in fact, some had low amphibian density, richness, and diversity. Further analyses of the subset of ponds represented in the peak of the area distribution showed that fish, hydroperiod, invertebrate density, and canopy are additional factors that drive density, richness and diversity of ponds up or down, when extremely small or large ponds are eliminated. Our results indicate that fishless ponds at intermediate sizes are more diverse, produce more larvae, and have greater potential to recruit juveniles into adult populations of most species sampled. Further, hylid and chorus frogs are found predictably more often in ephemeral ponds whereas bullfrogs, green frogs, and cricket frogs are found most often in permanent ponds with fish. Our data increase understanding of what factors structure and maintain amphibian diversity across large landscapes.

Spatial distribution, temporal variation and specificity of microhabitat of Tropisternus species (Coleoptera: Hydrophilidae) in permanent ponds.

The spatial distribution and temporal variation of 11 species of Tropisternus were analyzed in two permanent ponds located in the province of Corrientes, Argentina. Samples were collected every 15 days, between October 2010 and March 2011. The species recorded were Tropisternus collaris (Fabricius), Tropisternus ovalis Castelnau, Tropisternus laevis (Sturm), Tropisternus lateralis limbatus (Brullé), Tropisternus longispina Fernández & Bachmann, Tropisternus carinispina Orchymont, Tropisternus bourmeisteri Fernández & Bachmann, Tropisternus apicipalpis (Chevrolat), Tropisternus dilatatus Bruch, Tropisternus obesus Bruch, and Tropisternus ignoratus Knisch. The first four were present in higher proportions than the remaining during most of the study period. The spatial distribution of individuals was mostly related to the homogeneity or heterogeneity of the ecosystem in relation to microhabitats with aquatic vegetation: In ponds with different microhabitats, individuals were mainly aggregated, whereas in ponds with homogenous features, individuals were randomly distributed. However, when species were analyzed individually, the spatial distribution and the use of microhabitat by each species were different with respect to preference and behavior.

Long-term monitoring of astatic water bodies: microcrustaceans as indicators of hydroperiod length in ponds and pools

Microcrustacean assemblages (Cladocera and Copepoda) from astatic ponds and pools of Castelporziano Presidential Estate were analysed to evaluate their role as indicators of functional variations related to the duration of the wet phase. Samples from a subset of 23 water bodies classified as permanent or temporary (based on observations over two decades, 1989–2010) were analysed. As a whole, 36 species of microcrustaceans were present. Hierarchical clustering allowed a clear distinction between temporary and permanent water bodies. Principal coordinates analysis (PCoA) provided a good separation of the two major hydroperiod groups along the first axis, while no correlation emerged among PCoA axes and hydrogeological setting. The correlation between species and the first PCoA axis highlighted biological indicators of hydrological change: among them, the cyclopoid copepods Macrocyclops albidus and Eucyclops serrulatus, which have no resting stages, were exclusive of permanent ponds; the calanoid copepod Eudiaptomus padanus etruscus and the cladocerans Ceriodaphnia reticulata, Scapholeberis rammneri and Coronatella rectangula were present in permanent and semi-permanent ponds; the cladoceran Daphnia chevreuxi and the calanoid copepods Diaptomus serbicus, Hemidiaptomus gurneyi and Mixodiaptomus kupelwieseri were exclusive of temporary ponds with short hydroperiod (less than 6 months). Temporary water bodies hosted a higher mean species richness (13.7 species) than permanent ones (10.3), and the difference was statistically significant. Our results highlight that: (1) the cladoceran and copepod assemblage effectively discriminate between ponds with different wet phase duration, proving to be good bioindicator; (2) small astatic water bodies play an important role in biodiversity conservation, as they host a high percentage of the species distributed over wider areas, next to species which are exclusively found in these habitats; (3) hydroperiod appears to be the main driving force in characterising microcrustacean assemblages in astatic ponds.

Low impact of chytridiomycosis on frog recruitment enables persistence in refuges despite high adult mortality

The global chytridiomycosis pandemic caused by the pathogen Batrachochytrium dendrobatidis (Bd) is implicated in the apparent extinction or severe decline of over 200 amphibian species. Many declined species now only persist in isolated remnant populations. In this study we examine how remnant populations coexist with Bd, focusing on disease impact on adult survival and recruitment potential in the chytridiomycosis-threatened frog Litoria verreauxii alpina. Using skeletochronology we found that the adult male population in both 2011 and 2012 was dominated by a two year old age cohort. The lack of recruitment into the three year old cohort in 2012 indicates that annual adult survival is very low. Combined with high Bd prevalence and heavy infection burdens, the pathogen appears to drive almost complete mortality of breeding adults over their first breeding season. However, adults successfully mate prior to large increases in disease prevalence that occurs during the breeding season. Infection prevalence among tadpoles and juveniles is low. Exposure to warm water could provide a mechanism for avoiding or clearing Bd infection. Relatively low Bd prevalence in juveniles prior to dispersal into terrestrial habitat indicates that Bd has minimal impact on early life history stages. As such, recruitment is probably high, allowing populations to persist despite low adult survival. This dependence on reliable annual recruitment may explain why remnant populations persist in permanent ponds rather than ephemeral ponds that were historically occupied. New management strategies that focus on increasing recruitment may provide a way forward for the management of disease-threatened amphibian species.

Diversidade de anfíbios anuros de uma área de Pampa no município de São Gabriel, Rio Grande do Sul, Brasil

Considerado um bioma ameaçado, o Pampa possui um dos menores percentuais de área legalmente protegida. Além disso, o conhecimento sobre comunidades de anuros neste bioma ainda é escasso. Nesse contexto, o objetivo deste estudo foi determinar a composição de anuros em uma área de Pampa no sul do Brasil. Entre janeiro de 2009 e fevereiro de 2010 foi realizado um inventário na Fundação Estadual de Pesquisa Agropecuária do município de São Gabriel, Rio Grande do Sul. A procura dos exemplares foi realizada em poças permanentes, semi-permanentes e temporárias pelo método de levantamento em sítio de reprodução. Foram registradas 21 espécies pertencentes a cinco famílias, o que corresponde a aproximadamente 20% das espécies do estado e 42% das espécies conhecidas para a ecorregião Savana Uruguaia. Dez espécies foram consideradas frequentes, sete comuns e quatro foram raras. Foram registrados três modos reprodutivos, sendo que 57% das espécies utilizam o modo 1, que parece estar relacionado à homogeneidade da área. A análise de agrupamento comparando a composição de anuros de quatro localidades distintas mostrou maior similaridade com o município de Candiota (região da Campanha). As espécies presentes na área de estudo são associadas a formações campestres do estado e países vizinhos e podem ser consideradas típicas do bioma Pampa.

The response of amphibian communities to fish and habitat features in Mediterranean permanent ponds

Generalized linear models were used to test the effect of fish, using ponds with and without fish and habitat features as covariates, on richness and abundance of amphibian species. Five fish species and six amphibian species were recorded in 60 permanent ponds located in central Italy. The choice of covariates (macrophyte cover and pond surface area) was made after studying the correlations. The richness of amphibian species was not significantly affected by fish presence or macrophyte cover, in line with previous studies, since almost all the fish species were non-predatory. However, abundance of urodeles (newts) was negatively affected by fish and positively affected by macrophyte cover. Although fish may strongly influence the abundance and composition of amphibian communities, the results indicate that the cover of aquatic macrophytes may increase the available habitat for amphibians and therefore their abundance. Anuran species preferred ponds where fish were present, since both groups preferred larger ponds. Concordance between fish and amphibian species composition was not found by the Mantel and Partial Mantel tests. This indicates that the fish assemblages do not predict which amphibian species occur in the pond.

Anfíbios anuros em uma área de Mata Atlântica da Serra do Tabuleiro, Santa Catarina

Anuran amphibians in an Atlantic Forest area at Serra do Tabuleiro, Santa Catarina, Brazil. The Atlantic Forest is a priority area for the conservation of amphibians, with some regions already showing knowledge gaps. We analyzed the composition and richness of anuran species in an area of dense ombrophilous forest at Serra do Tabuleiro, the seasonal richness variation, and the daily activity of males during vocalization shifts. We collected samples of anurans from two permanent ponds and from a track within the forest for 14 months. We recorded 32 anuran species, among which Aplastodiscus cochranae, A. ehrhardti, and Hypsiboas poaju are

A mathematical model of the repopulation of southern high plains playas by Ambystoma tigrinum following Antevs’ Altithermal

The 20,000 ephemeral ponds, the playas of the southern high plains of the United States, were thought to have experienced a prolonged drought ending approximately 5000years ago, during which amphibians and other aquatic residents would have died out. A few permanent ponds are conjectured to be the source of repopulation of the entire region since then. We develop a series of mathematical models based on the tiger salamander, Ambystoma tigrinum, on rainfall data, and on field data, to test this hypothesis. We show that, under reasonable assumptions, the region could have been repopulated through migration within this time frame.

Plastic patterns in larval development of Endangered endemic Atelognathus patagonicus: implications for conservation strategies

The Patagonia frog Atelognathus patagonicus (Anura, Ceratophryidae) is endemic to north-western Patagonia where it inhabits permanent and temporary water bodies in a system of endorheic ponds on the basaltic plateau in and around Laguna Blanca National Park, north- western Patagonia, Argentina. This Endangered species is emblematic of the decline and extinc- tion of amphibian populations as a result of the introduction of fish to Laguna Blanca. Therefore, the aims of this study were to determine the patterns of larval development in ponds with different hydro periods and to evaluate the occurrence of different developmental strategies and their impli- cations for conservation management. In permanent ponds, A. patagonicus tadpoles showed a double strategy, with the presence of both seasonal (short larval period; metamorphs in the same growing season) and overwintering tadpoles (undergoing metamorphosis the following spring). In temporary ponds, desiccation seems to exert great pressure, with accelerated larval development, resulting in short larval periods. Atelognathus patagonicus showed plasticity in the length of larval development, adjusting to the different hydroperiods observed in these wetlands. As a result of this dual strategy, overwintering tadpoles in permanent ponds are larger than seasonal tadpoles. This notable plasticity in developmental strategy enables this species to colonize widely varying environments. These results highlight the importance of preserving a variety of wetlands, includ- ing both temporary and permanent ponds, to allow this species to continue to breed and develop in the face of current and potential anthropogenic disturbance, in particular that caused by the activity of local native pastoralists.

Breeding site heterogeneity reduces variability in frog recruitment and population dynamics

Environmental stochasticity can have profound effects on the dynamics and viability of wild populations, and habitat heterogeneity provides one mechanism by which populations may be buffered against the negative effects of environmental fluctuations. Heterogeneity in breeding pond hydroperiod across the landscape may allow amphibian populations to persist despite variable interannual precipitation. We examined recruitment dynamics over 10yr in a high-elevation Columbia spotted frog (Rana luteiventris) population that breeds in ponds with a variety of hydroperiods. We combined these data with matrix population models to quantify the consequences of heterogeneity in pond hydroperiod on net recruitment (i.e. number of metamorphs produced) and population growth rates. We compared our heterogeneous system to hypothetical homogeneous environments with (1) only ephemeral ponds, (2) only semi-permanent ponds, and (3) only permanent ponds. We also examined the effects of breeding pond habitat loss on population growth rates. Most eggs were laid in permanent ponds each year, but survival to metamorphosis was highest in the semi-permanent ponds. Recruitment success varied by both year and pond type. Net recruitment and stochastic population growth rate were highest under a scenario with homogeneous semi-permanent ponds, but variability in recruitment was lowest in the scenario with the observed heterogeneity in hydroperiods. Loss of pond habitat decreased population growth rate, with greater decreases associated with loss of permanent and semi-permanent habitat. The presence of a diversity of pond hydroperiods on the landscape will influence population dynamics, including reducing variability in recruitment in an uncertain climatic future.

Variations in sediment organic carbon among different types of small natural ponds along Druridge Bay, Northumberland, UK

Small natural ponds from Druridge Bay, Northumberland (UK), were sampled to investigate the variations in sediment organic carbon (OC) content among pond types. Sediment OC was highest in uncompacted sediments from permanent ponds with extensive natural vegetation (means ranged between 7.68 and 12.86% OC) but lower in compacted sediments (mean 3.72% OC) or from ponds in arable or pasture fields (mean 3.44% OC) and from adjacent soil controls (means of 3.13–3.38% OC). The extent of 4 distinct pond types (permanent naturally vegetated, arable field, grass pasture field, and dune slack) varied across years. This study highlights ecological variations among pond types that can result in large variations in sediment OC content and, combined with annual variations to the extent of ponds, poses significant implications for upscaling carbon burial rates based solely on combined surface area.

A new species of Scinax Wagler, 1830 (Anura: Hylidae) from the middle Amazon river basin, Brazil

A new species of the hylid genus Scinax is described and illustrated. The new taxon was found in the Amazonian rainforest of northern Brazil, municipalities of Maués and Careiro da Várzea, state of Amazonas. The new species is characterized by its moderate size (male mean snout-vent length 36.3mm); body robust; large, orange, black-bordered axillary and inguinal spots; and bilobate vocal sac. This new species was found in primary and secondary forest on branches of shrubs or trees in, or next to, permanent ponds and flooded areas.

A new species of the genus Tropodiaptomus (Copepoda, Diaptomidae, Diaptominae) from Nepal

A new species, Tropodiaptomus defayeae n. sp. from Nepal, is herein proposed for inclusion in the genus Tropodiaptomus. This is the first record of the genus from Nepal. The new species is described and illustrated based on two males and two females collected from a permanent freshwater pond in the village Ankidha near Khatmandu, Nepal. A critical comparison of the new species with its known congeners has revealed close similarity with Tropodiaptomus ruttneri (Brehm, 1923). However, it is distinguishable by characters of the male P5 such as: (1) a thick basipod in the right P5, which is as long as wide, and has an unusually large thumb-like hyaline lobe close to the inner margin on its posterior face; (2) a small spine and a narrow hyaline lamella on the inner margin; and (3) the basipod of the left P5 has a large hyaline lamella on the inner distal margin. Besides the description of T. defayeae, brief notes on the ecology and zoogeography of the genus are also given. A key for the identification of the Indian species of Tropodiaptomus, including also the new species, is provided at the end of this paper.

Biología de metacercarias <i>Kalipharynx</i> sp. (Trematoda: Digenea) en <i>Biomphalaria</i> (Gasteropoda: Planorbidae) del noreste argentino

In Argentina, no ecological studies have been reported on the infection parameters of Kalipharynx sp. metacercariae in planorbid snails. To this end, the aims of this study were: (i) to provide information on the population biology of Kalipharynx sp. metacercariae in the planorbid snails Biomphalaria tenagophila and B. occidentalis through the study of prevalence and intensity of larval infection during a seasonal cycle; (ii) to evaluate the effects of host shell size on prevalence and infection intensity, (iii) to evaluate the effect of infection intensity on cyst size. Samples were taken between June 2010 and April 2011 (encompassing all seasons) from a subtropical permanent pond in Corrientes City, Corrientes, Argentina. A total of 362 metacercariae (n=262 and n=100; from B. tenagophila and B. occidentalis respectively) were collected from 616 snails (n=466 and n=150 from B. tenagophila and B. occidentalis respectively). The metacercarial cysts were found in the digestive gland, mantle cavity, intestine and ovotestis. B. tenagophila showed a range of infection from 1 to 60 cysts per snail (mean = 4.5 +/- SD=9.9), and cyst diameter ranging between 255 and 705 microm (466.4 +/- 119); while, B. occidentalis showed a range of infection from 1 to 23 (5.5 +/- 5.6), and cyst diameter ranging between 310 to 900 microm (554.5 +/- 150). Results obtained indicated that, although absent in autumn, metacercariae of Kalipharynx sp. were present most of the year in both species of Biomphalaria, showing high values in both warm-season. Furthermore, both the infection intensity and host shell size varied significantly between seasons, although no seasonal variation was observed with respect to metacercarial cyst size, suggesting the possibility of more than one peak of cercariae emergence during the year. The prevalence of infection was significantly and positively correlated with snail size in both host species (p<0.05). The smallest host size class harbouring a metacercarial infection was 7.1-8.0 mm and 11.1-12.0 mm in B. tenagophila and B. occidentalis, respectively. The mean intensity of infection was positively correlated with snail size, but this relation was significant only in B. tenagophila (p < 0.05). However, non-significant negative correlations were observed for intensity of infection vs. cyst size in both host species (p > 0.05). The results of this study show a significant influence of host size on prevalence and infection intensity, and a tendency towards density-dependent reductions in the growth of cysts. This is the first study in Argentina analyzing the population biology of Kalipharynx sp. metacercariae.