The soil nematode fauna of five locations situated in Parque Nacional del Agua (PNA) in Costa Rica is characterized and analyzed. Four ecosystems were sampled in each location: primary (undisturbed) forest, secondary (naturally regenerated) forests, tree plantations (cleared and replanted with timber trees), and pastures (cleared of trees). Five soil samples of 100 g were analyzed in each location and ecosystem, resulting in a total of 100 samples. One hundred and thirty-one nematode genera were identified, and their abundance and biomass were estimated and analyzed by means of nonmetric multidimensional scaling (NMDS) and redundancy analysis (RDA). The observed nematode abundance was 1237 ± 520 specimens per soil sample for the whole survey, similar to previously reported from tropical soils. Dominance-diversity curves, based on nematode abundance, follow a similar ‘hollow curve’ pattern, with only 20 of the genera representing 84.6% of the total abundance, and only 12 of the genera representing 88% of the total biomass. Helicotylenchus, tylenchids, criconematids, Belondira, Longidorus, Xiphinema, Monotrichodorus, Prismatolaimus and Steinernema are important in the assemblages due their abundance or biomass in the different samples. Monotrichodorus and Discocriconemella appear related to undisturbed ecosystems, and they could have potential as disturbance indicators. Biomass-based dominance-diversity curves have similar qualitative and quantitative behavior to those observed in abundance distribution, but the dorylaims, Aporcelinus and Aporcelaimoides, which represented only the 0.35% of the abundance, having a major part of the total biomass (4.33%). NMDS analysis segregated locations into two groups, sampled sites were arranged according to the life zone where they belong. Ecosystems were segregated into natural ecosystems and plantations but having overlapping zones. Whereas RDA analysis indicated that organic matter and Cu are the most relevant edaphic variables for explaining the distribution of nematode assemblages, however few genera appear important in the ordination, Mesocriconema, Longidorus, Xiphinema and Belondira between them.

The soil nematode fauna of five locations situated in Parque Nacional del Agua (PNA) in Costa Rica is characterized and analyzed. Four ecosystems were sampled in each location: primary (undisturbed) forest, secondary (naturally regenerated) forests, tree plantations (cleared and replanted with timber trees), and pastures (cleared of trees). Five soil samples of 100 g were analyzed in each location and ecosystem, resulting in a total of 100 samples. One hundred and thirty-one nematode genera were identified, and their abundance and biomass were estimated and analyzed by means of nonmetric multidimensional scaling (NMDS) and redundancy analysis (RDA). The observed nematode abundance was 1237 ± 520 specimens per soil sample for the whole survey, similar to previously reported from tropical soils. Dominance-diversity curves, based on nematode abundance, follow a similar ‘hollow curve’ pattern, with only 20 of the genera representing 84.6% of the total abundance, and only 12 of the genera representing 88% of the total biomass. Helicotylenchus, tylenchids, criconematids, Belondira, Longidorus, Xiphinema, Monotrichodorus, Prismatolaimus and Steinernema are important in the assemblages due their abundance or biomass in the different samples. Monotrichodorus and Discocriconemella appear related to undisturbed ecosystems, and they could have potential as disturbance indicators. Biomass-based dominance-diversity curves have similar qualitative and quantitative behavior to those observed in abundance distribution, but the dorylaims, Aporcelinus and Aporcelaimoides, which represented only the 0.35% of the abundance, having a major part of the total biomass (4.33%). NMDS analysis segregated locations into two groups, sampled sites were arranged according to the life zone where they belong. Ecosystems were segregated into natural ecosystems and plantations but having overlapping zones. Whereas RDA analysis indicated that organic matter and Cu are the most relevant edaphic variables for explaining the distribution of nematode assemblages, however few genera appear important in the ordination, Mesocriconema, Longidorus, Xiphinema and Belondira between them. | Se caracteriza la fauna de nematodos del suelo de cinco localidades ubicadas en el Parque Nacional del Agua (PNA) en Costa Rica. y analizado. Se muestrearon cuatro ecosistemas en cada ubicación: bosque primario (no perturbado), bosque secundario bosques (regenerados naturalmente), plantaciones de árboles (taladas y replantadas con árboles maderables) y pastos (talados de árboles). Se analizaron cinco muestras de suelo de 100 g en cada localidad y ecosistema, resultando un total de 100 muestras. Se identificaron ciento treinta y un géneros de nematodos y se determinó su abundancia y biomasa. estimado y analizado mediante escalamiento multidimensional no métrico (NMDS) y análisis de redundancia (RDA). La abundancia de nematodos observada fue de 1237 ± 520 especímenes por muestra de suelo durante todo el estudio. similar a lo reportado previamente en suelos tropicales. Curvas de dominancia-diversidad, basadas en la abundancia de nematodos, siguen un patrón similar de "curva hueca", con sólo 20 de los géneros representando el 84,6% de la abundancia total, y sólo 12 de los géneros representan el 88% de la biomasa total. Helicotylenchus, tylénquidos, criconemátidos, Belondira, Longidorus, Xiphinema, Monotrichodorus, Prismatolaimus y Steinernema son importantes en los ensamblajes. debido a su abundancia o biomasa en las diferentes muestras. Aparecen Monotrichodorus y Discocriconemella relacionados con ecosistemas no perturbados, y podrían tener potencial como indicadores de perturbación. Basado en biomasa Las curvas de dominancia-diversidad tienen un comportamiento cualitativo y cuantitativo similar a las observadas en abundancia. distribución, pero los dorylaims, Aporcelinus y Aporcelaimoides, que representaron sólo el 0,35% de la abundancia, representando la mayor parte de la biomasa total (4,33%). El análisis NMDS separó las ubicaciones en dos En los grupos, los sitios muestreados se ordenaron según la zona de vida a la que pertenecen. Los ecosistemas estaban segregados en ecosistemas naturales y plantaciones pero con zonas superpuestas. Mientras que el análisis de RDA indicó que la materia orgánica y el Cu son las variables edáficas más relevantes para explicar la distribución de los ensambles de nematodos, sin embargo pocos géneros parecen importantes en la ordenación, Mesocriconema, Longidorus, Xiphinema y Belondira entre ellos. | Universidad Nacional, Costa Rica | Elsevier, Países Bajos | Escuela de Ciencias Biológicas

ABSTRACT This study estimated the population density of Spondylus limbatus at six fishing banks that are representative of the Gulf of California, Mexico. Each bank was identified in July 2011. There were significant differences in density between banks, and a steady north-to-south decrease in density that was fitted to a potential model. At low densities, S. limbatus showed a lower variability in size. Since the densities of S. limbatus are suitable for commercial exploitation, sustainable extraction can be performed under a population recovery approach. Also, this study represents a baseline for the evaluation and monitoring of populations of this species through time and contributes to set general guidelines for the assessment of commercial feasibility and exploitation criteria.

El Sistema Nacional de Áreas Protegidas (SINAP) cumple los compromisos de conservación y promoción de los recursos naturales en el territorio nacional generando proyectos de investigación con el fin de determinar la calidad de sus recursos, a través de planes de manejo territorial. La Territorial Amazonía lleva a cabo el monitoreo de recursos dentro de las áreas protegidas y las zonas de influencia de los 5 departamentos de la Región Amazónica, por lo que se vuelve un objetivo la caracterización del recurso hídrico para determinar la calidad del mismo y el impacto de fenómenos antrópicos en el territorio que podrían afectar dicho recurso. Este estudio se desarrolló en el municipio de El Retorno, en el departamento de Guaviare (Colombia), se realizó un levantamiento de información en tres Reservas Naturales de la Sociedad Civil (RNSC) en donde cruzan tres diferentes afluentes que desembocan en Caño Grande en la zona de influencia de la Reserva Natural Nacional Nukak (RNN Nukak). El estudio se realizó durante los meses de julio a diciembre del año 2021 en un total de nueve estaciones, en donde se hizo un reconocimiento de la zona a través del índice QBR, para la determinación de calidad de agua se midieron parámetros fisicoquímicos con un multiparámetro HANNA HI9829, y se utilizó el índice biológico de calidad BMWP_Col/ASPT para el cual se colectaron muestras de macroinvertebrados acuáticos a través de colecta manual y Red D (1mm) teniendo en cuenta los valores de abundancia y riqueza. Los datos fueron analizados a través de un análisis de correspondencia canónica y una agrupación clúster según las abundancias. Se obtuvo una relación significativa con respecto a variables ambientales de temperatura, saturación de oxígeno y oxígeno disuelto, una menor relación con respecto al cambio del pH y caudal; las abundancias más altas fueron de las familias Chironomidae y Elmidae, según la diversidad se determinó que la estación 3P (Caño Palo Grueso) fue la más biodiversa. | Dirección Territorial Amazonía - RNN Nukak | Biólogo | Pregrado | The National System of Protected Areas (SINAP) fulfils the commitments of conservation and promotion of natural resources in the national territory by generating research projects in order to determine the quality of its resources, through territorial management plans. The Amazon Territory carries out the monitoring of resources within protected areas and zones of influence of the 5 departments of the Amazon Region, so it becomes an objective the characterization of water resources to determine their quality and the impact of anthropogenic phenomena in the territory that could affect this resource. This study was carried out in the municipality of El Retorno, in the department of Guaviare (Colombia). Information was collected in three Civil Society Nature Reserves (RNSC) where three different tributaries flow into Caño Grande in the area of influence of the Nukak National Nature Reserve (RNN Nukak). The study was conducted during the months of July to December 2021 in a total of nine stations, where a reconnaissance of the area was made through the QBR index, for the determination of water quality physicochemical parameters were measured with a multiparameter HANNA HI9829, and the biological quality index BMWP_Col/ASPT was used for which samples of aquatic macroinvertebrates were collected through manual collection and Red D (1mm) taking into account the values of abundance and richness. The data were analysed by canonical correspondence analysis and clustering according to abundance. A significant relationship was obtained with respect to environmental variables of temperature, oxygen saturation and dissolved oxygen, a lesser relationship with respect to pH change and flow rate; the highest abundances were of the families Chironomidae and Elmidae, according to diversity it was determined that station 3P (Caño Palo Grueso) was the most biodiverse.

Se analiza la distribución, abundancia relativa y composición de especies del orden Euphausiacea en el mar ecuatoriano, en el período septiembre-octubre de 1999 (CO-II-99). De un total de 25047 org/1000m³ se identificaron las siguientes especies Nyctiphanes simplex; Euphausia distinguenda; E. diomedeae; E. tenera; Stylocheiron sp., S. carinatum; S. longicorne; Nematoscelis sp., N. gracilis; N. tenella; Nematobrachion flexipes y Thysanopoda orientalis. La información biológica obtenida se correlaciona con las condiciones físicas del océano observadas durante el período de estudio. Se destaca la abundancia de Nyctiphanes simplex, en el área de influencia de la Corriente de Humboldt. La distribución de las especies propias de aguas tropicales y subtropicales como Euphausia diomedeae, E. distinguenda, E. tenera, Stylocheiron carinatum, S. longicorne; Nematobrachion flexipes, Nematoceslis gracilis, N. Tenella, guardan relación con las masas de agua reportadas. Se registró por primera vez la presencia de Thysanopoda orientalis y su incursion en esta región debe ser estudiada con mas detalle. | This study examines the distribution, relative abundance and composition of the order Euphausiacea species in the Pacific Ocean off the coast of the Galapagos Islands, from the period of September 1, 1999 through October 31, 1999. A total of 25,047 org/1000m³, the following species were identified: Nyctiphanes simplex; Euphausia distinguenda; E. diomedeae; E. tenera; Stylocheiron sp., S. carinatum; S. longicorne; Nematoscelis sp., N. gracilis; N. tenella; Nematobrachion flexipes and Thysanopoda orientalis. This research correlates biological information obtained from the physical conditions of the ocean observed during the period of the study. The abundance of Nyctiphanes simplex in the Humboldt Current is detected . The distribution of species characteristic of tropical and subtropical waters such as Euphausia diomedeae, E. distinguenda, E. tenera, Stylocheiron carinatum, S. longicorne, Nematocrachion flexipes, Nematoceslis gracilis, and N. Tenella, are in normal relationship with the reported water masses. The presence Thysanopoda orientalis is registered for the first time in the region of the Galapagos Islands, and its presence must studied very carefully. | Incluye ref.bibl., grafs. | Published | Krill

Introduction: Scolopacidae family (Order: Charadriiformes) is one of the most abundant families found in coastal wetlands. La Arenilla coastal wetland has a historical record of 20 scolopacid species; climatic events could affect the distribution and migration of the several species of this taxonomic family, reducing their species richness and abundance. Objective: The aim of the present study was to determine the relationship between richness and abundance of the species belonging to the Scolopacidae family and both Sea Surface Temperature (SST) and the coastal El Niño index (ICEN) in La Arenilla Coastal Wetland, La Punta, Callao. Methods: Sampling were carried out twice a month, between January 2013 and January 2019 using the Total Count Method in order to determine species abundance (N = 292). A Spearman correlation analysis between abundance, species richness, SST and ICEN was performed, and beta diversity was calculated through the Whittaker index (βw) to analyze both the annual turnover for each season and the seasonal turnover within each year. Results: Two significant correlations were obtained: between SST and abundance and between ICEN and species richness. On the other hand, the ANOSIM test showed seasonal differences in abundance, and the SIMPER test showed that the greatest difference in abundance between seasons was between autumn and spring (Bray-Curtis dissimilarity = 81.57 %), and the minimum difference between winter and spring (Bray-Curtis dissimilarity = 49.86 %). Conclusions: The ecological dynamics of scolopacid communities in La Arenilla coastal wetland face important changes according to the variations in the environmental thermal parameters related to climate change.   | Introducción: La familia Scolopacidae (Orden: Charadriiformes) es una de las familias más abundantes en los humedales costeros. El Humedal Costero Poza de la Arenilla cuenta con un registro histórico de 20 especies de escolopácidos; los eventos climáticos podrían afectar la distribución y migración de varias especies de esta familia taxonómica, reduciendo su riqueza y abundancia. Objetivo: Determinar la relación entre la riqueza y la abundancia de las especies pertenecientes a la familia Scolopacidae y la temperatura superficial del mar (TSM) y el índice costero El Niño (ICEN) en el Humedal Costero Poza de la Arenilla. Métodos: Se realizaron muestreos dos veces por mes entre enero 2013 y enero 2019 utilizando el método del conteo total para determinar la abundancia de las especies (N = 292). Se realizó un análisis de correlación de Spearman entre la abundancia, riqueza, TSM e ICEN, y se procedió a calcular la diversidad beta a través del índice de Whittaker, tanto para analizar el recambio anual para cada estación como el recambio estacional dentro de cada año. Resultados: Se obtuvieron dos correlaciones significativas: entre TSM y abundancia y entre ICEN y riqueza. Por otro lado, la prueba ANOSIM arrojó diferencias estacionales en las abundancias de las especies, y la prueba SIMPER arrojó que la mayor diferencia en las abundancias entre estaciones fue entre otoño y primavera (disimilitud de Bray-Curtis = 81.57 %), y la mínima entre invierno y primavera (disimilitud de Bray-Curtis = 49.86 %). Conclusiones: Las dinámicas ecológicas de las comunidades de escolopácidos en La Arenilla se ven modificadas de manera importante en función a las variaciones de los parámetros térmicos ambientales relacionados al cambio climático.  

The "Metabolic Theory of Ecology (MTE) uses temperature as the environmental variable that predicted diversity patterns of ectothermic organisms. Specifically, the MTE predicts that the relationship between species richness (dependent variable) and the inverse of temperature (independent variable) has a slope ranging from -0.6 and -0.7. Thus, this study tested whether the pattern of species richness of freshwater fishes in Brazilian reservoirs fits of the MTE predictions. Besides temperature, other variables (potential evapotranpiration, actual evapotranspiration, precipitation, net primary productivity, elevation, age and area of reservoirs and b of EER - Energetic Equivalence Rule - slope of the relationship between body size and abundance of species) were used to test the MTE predictions. The MTE was tested using data from compilations (without control of the sampling effort) and sampled data (with standardized effort). For the latter data set all the MTE assumptions (ectothermic organisms, with high levels of taxonomic organization and whose body size and abundance do not vary spatially) were met. The tests were performed using OLS regressions and autoregressive models (SAR) and spatial filtering approach were used to minimize the effects of spatial autocorrelation when it was detected. To evaluate whether the lack of fit to the MTE predictions results from the violation of the spatial invariance assumption in abundance and species body size, it was added the slope's values of the b of EER as a predictor variable. The Akaike Information Criterion was used to select the best model and the spatial filters approach was used to minimize the autocorrelation when it was present. Partial regressions were used to evaluate the pure effect of the different components (local, regional, spatial/population) for the explanation of species richness. It was found that the species number increased toward the lower latitudes. The analyses for compiled data revealed consistency with the MTE predictions after removing the autocorrelation in the regression's residuals. For sampled data was not observed spatial autocorrelation in the regression residuals. However, the results were discordant with the MTE predictions, even adding the b of EER in model. For compiled data the variables temperature, precipitation and habitat age were retained in the best model, explaining 61.7% of the variation in the species richness after removing the spatial autocorrelation. Using the sampled data the same variables plus b EER were retained in the best model, which explained 90% of the variation in richness. Controlling the sampling effort and adding variables to the model originally proposed by the MTE, the slope of the relationship between species richness and temperature was consistent with the MTE predictions. The regional component effect (temperature and precipitation) contributed to explain the most variation of richness. We conclude that the MTE's failure in supporting empirical evidences should not be attributed to the assumptions violation and that the theory should consider the sampling effort control as an important condition to test the MTE prediction. The sampling effort control may reduce the problems of the spatial autocorrelation, besides generate parameters that modify quantitatively the results and qualitatively the interpretations. The relevant factors to the MTE's adjustment were the sampling effort control to obtain the specimens, no violation of assumptions and incorporating other variables in the model, which can vary substantially according to the taxonomic groups and habitats that occupy. | A "Teoria Metabólica da Ecologia" (MTE - Metabolic Theory of Ecology) usa a temperatura como variável ambiental preditora dos padrões de diversidade de organismos ectotérmicos. Especificamente, a MTE prediz que a relação entre riqueza (variável dependente) e temperatura (variável independente) apresenta um valor de inclinação de reta variando entre -0,6 e -0,7. Assim, este estudo testou se o padrão de riqueza de espécies de peixes de água doce em reservatórios brasileiros se ajusta às predições da MTE. Além da temperatura, outras variáveis (evapotransiração potencial, evapotranspiração atual, precipitação, produtividade primária líquida, elevação, idade e área dos reservatórios e b da EER (Energetic Equivalence Rule - inclinação da relação entre abundância e tamanho do corpo das espécies) foram usadas para testar as predições da MTE. Foi verificado se houve diferenças nos ajustes utilizando-se dados de riqueza provenientes de compilações (sem controle do esforço amostral) e amostragens (com controle do esforço amostral). Para este último conjunto de dados todos os pressupostos da MTE (organismos ectotérmicos; com altos níveis de organização taxonômica, cujo tamanho do corpo e abundância não variem espacialmente) foram atendidos. Os testes foram feitos utilizando-se regressões OLS, sendo que modelos autorregressivos (SAR) e abordagem de filtros espaciais foram utilizados para minimizar os efeitos da autocorrelação espacial quando esta foi detectada. Verificou-se também se a falta de ajuste dos dados à MTE é decorrente da violação do pressuposto da invariância espacial na abundância e tamanho do corpo das espécies acrescentando-se como preditor os valores do b da EER. O critério de informação de Akaike foi utilizado para selecionar o melhor modelo e regressões parciais utilizadas para avaliar o puro efeito dos diferentes componentes (local, regional, espacial/populacional) para a explicação da riqueza. No geral, verificou-se que o número de espécies aumentou em direção às menores latitudes. As análises para dados compilados revelaram compatibilidade com as predições da MTE após a remoção dos efeitos da autocorrelação espacial nos resíduos da regressão. Para dados amostrados não foi observada autocorrelação nos resíduos da regressão e os resultados mostraram-se bastante discordantes das predições da MTE, mesmo acrescentando-se o b da EER no modelo. Para dados compilados, as variáveis temperatura, precipitação e idade dos reservatórios foram constituintes do melhor modelo e explicaram 61,7% da variação na riqueza após a remoção da autocorrelação. As mesmas foram retidas para dados amostrados adicionando-se o b da EER, as quais explicaram 90% da variação da riqueza. Padronizando o esforço amostral e adicionando variáveis ao modelo originalmente proposto pela MTE, o valor da inclinação da relação entre a riqueza de espécies e a temperatura foi compatível com as predições da teoria. O puro efeito do componente regional (temperatura e precipitação) foi responsável pela maior porcentagem de explicação da riqueza. Foi possível concluir que a falha da MTE em suportar evidências empíricas não pode ser atribuída à violação dos pressupostos e que a teoria deveria assumir como condição importante o controle do esforço amostral, pois além de reduzir problemas de autocorrelação nos resíduos da regressão pode gerar parâmetros que modificam quantitativamente os resultados e qualitativamente as interpretações. Além disso, concluiu-se que os fatores relevantes para o ajuste da MTE foram o controle do esforço amostral, a não violação de pressupostos e a incorporação de outras variáveis no modelo, as quais podem variar de acordo com os grupos estudados e hábitats que ocupam. | PhD

The aim of this study was to assess the Oligochaeta assemblage structure, along exposure period of artificial substrates, relating to some environmental variables, in Different channels of upper Paraná River alluvial plain. The samples for the study of Oligochaeta assemblage in artificial substrates were collected monthly from October 2006 to October 2007, in Baia River, and Ipoitã and Curutuba channels. The two axis of Principal Components Analysis explained 57,57% of data variability total so that the first component described seasonal variations in sampling stations. A total of 6.290 individuals were recorded, after the experiment, in a total of 24 taxa, belonging to families Opistocystidae, Enchytraeidae, Naididae and Tubificidae. The highest Oligochaeta densities were recorded in Baia River and the lowest in the Ipoitã channel. According to Detrended Correspondence Analysis (DCA) was observed separation of collection stations and hydrological periods. Correlations verified between the axes of PCA and DCA indicated to water chemical and physical variables influenced the Oligochaeta species composition and density between the channels and collection months. The results obtained in the current study evidenced that the colonization process in artificial substrate by Oligochaeta assemblage differed between hydrological periods and channels, with changes in species composition, density, abundance dominance and richness. | O objetivo deste estudo foi avaliar a estrutura da assembleia de Oligochaeta em substratos artificiais ao longo do período de exposição na coluna de água, relacionandoa com algumas variáveis ambientais, em diferentes canais da planície aluvial do alto rio Paraná. As amostras para o estudo da assembleia de Oligochaeta em substratos artificiais foi coletada mensalmente de outubro de 2006 a outubro de 2007, no rio Baía e canais Curutuba e Ipoitã. Os dois primeiros eixos da análise de componentes principais explicaram 57,57% da variabilidade total dos dados, e o primeiro componente descreveu variações sazonais nas estações de amostragem. Após o experimento, total de 6.290 indivíduos foram registrados com 24 táxons, pertencentes às famílias Opistocystidae, Enchytraeidae, Naididae e Tubificidae. As maiores densidades de Oligochaeta foram registradas no rio Baía e as menores no canal Ipoitã. Baseando-se no diagrama de ordenação da análise de correspondência com remoção do efeito de arco (DCA), observou-se separação das estações de coletas e períodos hidrológicos. As correlações verificadas entre os eixos da PCA e DCA indicaram que as variáveis físicas e químicas da água influenciaram a composição e densidade das espécies de Oligochaeta entre os canais e os meses de coleta. Os resultados obtidos no presente estudo evidenciaram que o processo de colonização em substrato artificial pela assembleia de Oligochaeta diferiu entre os períodos hidrológicos e canais, com mudanças na composição, densidade, abundância, dominância e riqueza de espécies. | Masters

El propósito del presente estudio fue comprobar si han ocurrido cambios, después de 16 años, en los patrones de abundancia, distribución espacial y estructura de talla de la almeja de agua dulce Diplodon chilensis en sustratos arenosos y areno-pedregosos del sector Chauquén del Lago Panguipulli. Los resultados indican que las almejas en 1987 y 2003 presentan una distribución espacial agregada en ambos sustratos y con una mayor fuerza de la agregación en los sustratos areno-pedregosos que arenosos. La densidad fue significativamente mayor en sustrato areno-pedregoso, tanto en 1987 (P < 0,001) como en el 2003 (0,001< P < 0,01). No se presentaron diferencias significativas (P > 0,05) en densidad entre los distintos años dentro de un mismo tipo de sustrato. La estructura de talla en ambos sustratos y periodos estudiados no varió mayormente, registrándose sin embargo en 2003 juveniles en ambos sustratos, lo que indicaría que ha ocurrido reclutamiento. Se discuten estos resultados en relación al rol que desempeñan estos bivalvos en el ecosistema y en su potencial uso en la evaluación ecológica de ambientes lacustres.<br>The purpose of the present study was to verify eventual changes in spatial distribution, density and size structure in a population of Diplodon chilensis inhabiting sandy and sand-gravel substrates in the Lake Panguipulli after 16 years of studies carried out in the mentioned population. Results indicate that mussels show in 2003 an aggregated spatial distribution in both substrates and a more aggregated distribution in sand - gravel than sandy substrate as in 1987. As in 1987, density was significantly higher in sand - gravel substratum in 2003 (P < 0.01). There were not significantly differences in density within the period elapsed in the same type of substratum. Size structure of population did not show much changes. Nonetheless, young were registered in both substrates in 2003, indicating that recruitment occurred. The results are discussed in relation to the role of these bivalves in the ecosystem and their potential use in ecological evaluation of lacustrine environments.