Taxonomic and functional responses of macroinvertebrates to riparian forest conversion in tropical streams.

Land use change threatens the ecological integrity of tropical rivers and streams; however, few studies have simultaneously analyzed the taxonomic and functional responses of tropical macroinvertebrates to riparian forest conversion. Here, we used community structure, functional diversity, and stable isotope analyses to assess the impacts of riparian deforestation on macroinvertebrate communities of streams in southern Mexico. Monthly sampling during the dry season was conducted in streams with riparian forest (forest streams), and in streams with pasture dominating the riparian vegetation (pasture streams). Samples were collected for water quality (physical-chemical variables, nutrient concentrations, and total suspended solids), organic matter (leaf litter abundance and algal biomass), and macroinvertebrate abundance and diversity. Higher temperature, conductivity, suspended solids, and chlorophyll a were detected in pasture streams, while nitrate concentrations and leaf litter biomass were greater in forest streams. Macroinvertebrate density was higher in pasture sites, while no differences in taxonomic diversity and richness were found between land uses. Functional evenness was greater in forest streams, while richness and divergence were similar between land uses, despite differences in taxonomic composition. Environmental variables were associated with taxa distribution but not with functional traits, suggesting current conditions still promote redundancy in ecological function. Isotopic analyses indicated consumers in pasture streams were enriched in 13C and 15N relative to forest streams, potentially reflecting the higher algal biomass documented in pasture systems. Isotopic niches were broader and more overlapped in pasture streams, indicating more generalist feeding habits. No significant losses of taxonomic or functional diversity were detected in pasture streams. However, changes in trophic ecology suggest landscape-level processes are altering macroinvertebrate feeding habits in streams. The changes we observed in habitat, water quality, and macroinvertebrate community were related to the removal of the riparian vegetation, suggesting the structure and function of the focal systems would benefit from riparian restoration.

Patrones de distribución y estructura de la vegetación en el gradiente de humedales costeros El Castaño, Chiapas, México

Introducción: Las características de los humedales costeros son resultado de las interacciones hidrogeomorfológicas entre el continente y el océano, que causan un gradiente ambiental, que resulta en diferentes tipos de vegetación como manglares, popales, tulares, selvas y palmares inundables. Objetivo: Caracterizar las variables del hidroperiodo y fisicoquímicas del agua y suelo para determinar la relación que existe en el patrón de distribución de la vegetación en el Sistema de Humedales El Castaño (SHC). Metodología: Se establecieron 11 unidades de muestreo (UM) permanentes por estrato definidos: cinco en el manglar, dos en selvas inundables, dos en tular y dos en pastizal inundable. De mayo 2016 a octubre 2017 se caracterizó la vegetación y se muestreó mensualmente los niveles de inundación y parámetros fisicoquímicos del agua (superficial, intersticial y subterránea): salinidad, conductividad y pH; y el suelo: densidad aparente, porcentaje de humedad y potencial redox. Resultados: El manglar es el más cercano al mar, tiene la menor diversidad (H:1.66) y especies registradas (14), está dominado por Laguncularia racemosa y Rhizophora mangle y tiene los valores más altos de salinidad intersticial y subterránea, mayores a 10.8 ups, se mantiene inundado de 4 a 12 meses, su potencial redox es de 14.57 mV. Seguido está el manglar, tierra adentro, se ubican los remanentes de la selva inundable, (H:2.18 y 18 especies), dominada por Pachiraaquatica, la salinidad intersticial y subterránea de 4.95 ups, permanece inundada de 0 a 6 meses y el potencial redox es de 119.07 mV. El tular, después de la selva, (H:1.92 y 16 especies), dominado por Typha domingensis, salinidad intersticial y subterránea de 6.1 ups, el tiempo de inundación es de 5 a 8 meses y potencial redox es de 125.9 mV. El pastizal inundable, con menor influencia marina, es un humedal herbáceo modificado para uso ganadero, presentó los valores más altos de diversidad (H:3.44 y 50 especies), Paspalum conjugatum es la especie dominante, la salinidad intersticial y subterránea es menor a 0.5 ups, se mantiene inundado de 5 a 9 meses y el potencial redox es de 151.23 mV. Conclusiones: En cada tipo de vegetación, la estructura, composición y diversidad es diferente, con un alto recambio de especies que indica un gradiente definido por la salinidad. La vegetación en el SHC sigue los patrones de organización típica de los humedales costeros tropicales, manglares, selvas inundables y humedales herbáceos, en este caso los tulares y pastizales inundables. El factor que define la distribución de la vegetación, es salinidad y el gradiente que se observa está en función de la dinámica hidrológica que depende de entradas de agua marina y de la bajada de agua dulce del interior del continente.

Introduction: The characteristics of coastal wetlands are the result of hydrogeomorphological interactions between the continent and the ocean, which cause an environmental gradient, hat results in different vegetation types such as mangroves, freshwater marshes, swamp forests and palm swamps. Objective: To characterize the hydroperiod and physicochemical variables of water and soil and their effect on the distribution of vegetation in the Sistema de Humedales El Castaño. Methods: A total of 11 permanent sampling units (UM) were established by defined strata: five in the mangrove, two in swamp forest, two in freshwater marshes and two in the flooded pasture. From May 2016 to October 2017 the vegetation was characterized and the water levels and physicochemical parameters (superficial, interstitial and groundwater) were sampled monthly for: salinity, and pH; and the soil for: bulk density, humidity percentage, and redox potential. Results: Mangroves are the closest to the sea, have the lowest diversity (H: 1.66) and species richness (14), they are dominated by Laguncularia racemosa and Rhizophora mangle, have the highest values of interstitial and groundwater salinity, (> 10.8 ups), remain flooded for 4 to 12 months per year, and have a redox potential of 14.57 mV. Immediately, inland, there are remnants of the swamp forests (H: 2.18 and 18 species), dominated by Pachira aquatica, with 5 ups interstitial and groundwater salinity, flooded from 0 to 6 months per year, with a redox potential of 119.07 mV. These forests are followed inland by freshwater marshes (H: 1.92 and 16 species), dominated by Typha domingensis with 6.1 ups interstitial and groundwater salinity, flooded for 5 to 8 months per year and a redox potential of 125.9 mV. Finally, furthest inland is the flooded pasture, a modified herbaceous wetland for cattle grazing (H: 3.44 and 50 species) dominated by Paspalum conjugatum, where interstitial and groundwater salinity is less than 0.5 ups, it stays flooded for 5 to 9 months and the redox potential is 151.23 mV. Conclusions: In each type of vegetation, the structure, composition, and diversity are different, with a high turnover of species that indicates a gradient defined by salinity. The vegetation in the SHC follows the patterns of typical organization of the tropical coastal wetlands, mangroves, swamp forests and herbaceous wetlands, in this case the freshwater marshes and flooded pastures. The factor that define the distribution of the vegetation is the salinity and the gradient that is observed are a function of the hydrological dynamics that depends on the mixing of marine and freshwater.

[Avifauna in silvopastoral systems in the Mesoamerican Biological Corridor, Tabasco, México]. / Avifauna en sistemas silvopastoriles en el Corredor Biológico Mesoamericano, Tabasco, México.

Silvopastoral systems support local ecological and economical features as they enhance conservation of floral and faunal communities. As other animal communities, avifauna may be a good representative of habitat alterations, both as the species and functional levels. In order to attend the initiative of Mesoamerican Biological Corridor initiative (CBM) in the state of Tabasco, we studied the diversity of birds in two silvopastoral systems: scattered trees in pastures (ADP), and trees in boundary-hedgerows (AL). For this, we applied the fixed radius counting point method in three priority sites in Tabasco's CBM during the dry and wet season of 2011, and a total of 56, 60 and 62 points were evaluated in Huimanguillo, Tenosique and Tacotalpa, respectively. We observed 2 084 individuals of 154 species (79-89% of expected diversity) and 36 bird families. We detected 92, 87 and 85 species in Huimanguillo, Tenosique and Tacotalpa, respectively, including 35 protected species, of which 23, 19 and 16 in each locality, respectively. All sites showed high diversity (H' ≥ 3.20), low species dominance (D ≥ 0.08) and high equitability (J ≥ 0.77). Species composition showed differences between sites, being most similar Tacotalpa and Tenosique. Ten species were considered characteristic for sites. Although the silvopastoral system did contain protected species, the low diversity and the early successional character of the arboreal components were not attractive to frugivorous bird species. Diversification with native trees can improve the systems to create a complementary habitat and to increase landscape connectivity. The management of silvopastoral practices on cattle dominated landscapes in Tabasco could improve its ecological quality, and thus achieve the CBM's objectives ofbiodiversity conservation combined with human economic activities.

Avifauna en sistemas silvopastoriles en el Corredor Biológico Mesoamericano, Tabasco, México / Avifauna in silvopastoral systems in the Mesoamerican Biological Corridor, Tabasco, México

Silvopastoral systems support local ecological and economical features as they enhance conservation of floral and faunal communities. As other animal communities, avifauna may be a good representative of habitat altera- tions, both as the species and functional levels. In order to attend the initiative of Mesoamerican Biological Corridor initiative (CBM) in the state of Tabasco, we studied the diversity of birds in two silvopastoral systems: scattered trees in pastures (ADP), and trees in boundary-hedgerows (AL). For this, we applied the fixed radius counting point method in three priority sites in Tabasco´s CBM during the dry and wet season of 2011, and a total of 56, 60 and 62 points were evaluated in Huimanguillo, Tenosique and Tacotalpa, respectively. We observed 2 084 individuals of 154 species (79-89% of expected diversity) and 36 bird families. We detected 92, 87 and 85 species in Huimanguillo, Tenosique and Tacotalpa, respectively, including 35 protected species, of which 23, 19 and 16 in each locality, respectively. All sites showed high diversity (H´≥3.20), low species dominance (D≥0.08) and high equitability (J≥0.77). Species composition showed differences between sites, being most similar Tacotalpa and Tenosique. Ten species were considered characteristic for sites. Although the silvopastoral system did contain protected species, the low diversity and the early successional character of the arboreal components were not attractive to frugivorous bird species. Diversification with native trees can improve the systems to create a complementary habitat and to increase landscape connectivity. The management of silvopastoral practices on cattle dominated landscapes in Tabasco could improve its ecological quality, and thus achieve the CBM´s objectives of biodiversity conservation combined with human economic activities.

Los sistemas silvopastoriles contienen rasgos ecológicos y económicos que contribuyen con la conservación de comunidades florísticas y faunísticas que en ellas se desarrollan. Entre otras comunidades faunísticas se encuentra la avifauna la cual es un grupo representativo de las alteraciones del habitat, tanto a nivel específico como grupo functional. Con el objetivo de atender la iniciativa de Corredor Biológico Mesoamericano en Tabasco, México, se analizó la diversidad de aves en dos sistemas silvopastoriles: árboles dispersos en potreros (ADP) y árboles en cercos o linderos (AL). Se aplicó el método de punto de conteo de radio fijo en tres sitios prioritarios del CBM de Tabasco, ubicados en los municipios: Huimanguillo, Tacotalpa y Tenosique. Los datos provienen de las estaciones seca y húmeda del 2011. Se registraron 2 084 aves de 154 especies (79-89% del esperado) y 36 familias. Se detectaron 92, 87 y 85 especies, incluyendo 35 protegidas, con 23, 19 y 16 en Huimanguillo, Tacotalpa y Tenosique, respectivamente. Todos los sitios mostraron alta diversidad (H’≥3.20), baja dominancia de especies (D≥0.08) y alta equidad (J≥0.77). La composición de especies mostró diferencias entre sitios, con mayor similitud entre Tacotalpa y Tenosique. Diez especies pueden considerarse características de los sitios. Aunque en los sistemas silvopastoriles se refugian aves protegidas, el componente arbóreo es poco diverso y corresponde a especies de sucesión secundaria temprana, lo que limita a las aves frugívoras y especialistas de bosque. Diversificar estos sistemas con árboles nativos puede mejorar estos hábitats complementarios e incrementar la conectividad del paisaje para cumplir con los objetivos del CBM en la conservación de la biodiversidad y provisión de bienes a las poblaciones humanas.

[Microorganisms effect with probiotic potential in water quality and growth of the shrimp Litopenaeus vannamei (Decapoda: Penaeidae) in intensive culture]. / Efecto de microorganismos con potencial probiótico en la calidad del agua y el crecimiento de camarón Litopenaeus vannamei (Decapoda: Penaeidae) en cultivo intensivo.

The use of probiotics has gained acceptance in aquaculture, particularly in maintaining water quality and enhancing growth in organisms. This study analyzed the effect of the commercial (EM, Japan) natural product composed by (Rhodopseudomonas palustris, Lactobacillus plantarum, Lactobacillus casei and Saccharomyces cerevisiae) added to the water, in order to determine its effect in water quality, sediment and growth of L. vannamei under intensive culture. The evaluation included three treatments with a weekly addition of EM: i) tanks without probiotics (C), ii) tanks with a dose of 4 L/ha (EM1) and iii) tanks with a dose of 10 L/ha (EM2). The treatment C was carried out three times, while treatments EM1 and EM2 were carried out four times. A total of 4 350 shrimps were measured for total length and weight, to calculate total and porcentual weight gain, daily weight gain, specific growth rate (TCE), and food conversion factor (FCA); besides, the survival rate was estimated. The use of probiotics allowed a shorter harvest time in treatments EM1 (90 d) and EM2 (105 d) with relation to the treatment C (120d). Treatments EM1 and EM2 were within the recommended intervals for culture, with respect to treatment C. The use of probiotic bacteria significantly regulated pH (EM1, 8.03 +/- 0.33; EM2, 7.77 +/- 0.22; C, 9.08 +/- 0.35) and reduced nitrate concentration (EM1, 0.64 +/- 0.25 mg/L; EM2, 0.39 +/- 0.26 mg/L; C, 0.71 mg/L). Water pH mostly explained the variance with respect to the treatments. Treatment EM2 presented the greatest removal of organic matter (1.77 +/- 0.45%), whereas the contents of extractable phosphorus increased significantly in treatment EM1 with 21.6 +/- 7.99 mg/kg and in treatment EM2 with 21.6 +/- 8.45 mg/kg with control relation (14.3 +/- 5.47). The shrimp growth was influenced by dissolved oxygen, salinity and pH in the sediment, establishing that salinity was the most important variable in the weight with a negative association. Treatment EM1 recorded an improved TCE (2.69 +/- 0.35%/d) and FCA (1.46 +/- 0.20) with relation to the control treatment (TCE, 1.88 +/- 0.25%/d; FCA, 2.13 +/- 0.48). Survival was significantly greater in treatments containing probiotics with 61 +/- 8.76% and 60 +/- 10.5% for EM1 and EM2, respectively. This study indicated the positive effect obtained with the use of this commercial probiotic, to improve culture conditions and growth parameters in an intensive culture of L. vannamei.

Efecto de microorganismos con potencial probiótico en la calidad del agua y el crecimiento de camarón Litopenaeus vannamei (Decapoda: Penaeidae) en cultivo intensivo / Microorganisms effect with probiotic potential in water quality and growth of the shrimp Litopenaeus vannamei (Decapoda: Penaeidae) in intensive culture

The use of probiotics has gained acceptance in aquaculture, particularly in maintaining water quality and enhancing growth in organisms. This study analyzed the effect of the commercial (EM TM, Japan) natural product composed by (Rhodopseudomonas palustris, Lactobacillus plantarum, Lactobacillus casei and Saccharomyces cerevisiae) added to the water, in order to determine its effect in water quality, sediment and growth of L. vannamei under intensive culture. The evaluation included three treatments with a weekly addition of EM: i) tanks without probiotics (C), ii) tanks with a dose of 4L/ha (EM1) and iii) tanks with a dose of 10L/ha (EM2). The treatment C was carried out three times, while treatments EM1 and EM2 were carried out four times. A total of 4 350 shrimps were measured for total length and weight, to calculate total and porcentual weight gain, daily weight gain, specific growth rate (TCE), and food conversion factor (FCA); besides, the survival rate was estimated. The use of probiotics allowed a shorter harvest time in treatments EM1 (90d) and EM2 (105d) with relation to the treatment C (120d). Treatments EM1 and EM2 were within the recommended intervals for culture, with respect to treatment C. The use of probiotic bacteria significantly regulated pH (EM1, 8.03±0.33; EM2, 7.77±0.22; C, 9.08±0.35) and reduced nitrate concentration (EM1, 0.64±0.25mg/L; EM2, 0.39±0.26mg/L; C, 0.71mg/L). Water pH mostly explained the variance with respect to the treatments. Treatment EM2 presented the greatest removal of organic matter (1.77±0.45%), whereas the contents of extractable phosphorus increased significantly in treatment EM1 with 21.6±7.99mg/kg and in treatment EM2 with 21.6±8.45mg/kg with control relation (14.3±5.47). The shrimp growth was influenced by dissolved oxygen, salinity and pH in the sediment, establishing that salinity was the most important variable in the weight with a negative association. Treatment EM1 recorded an improved TCE (2.69±0.35%/d) and FCA (1.46±0.20) with relation to the control treatment (TCE, 1.88±0.25%/d; FCA, 2.13±0.48). Survival was significantly greater in treatments containing probiotics with 61±8.76% and 60±10.5% for EM1 and EM2, respectively. This study indicated the positive effect obtained with the use of this commercial probiotic, to improve culture conditions and growth parameters in an intensive culture of L. vannamei.

Los probióticos han ganado aceptación en la acuicultura para mantener la calidad del agua y aumentar el crecimiento de los organismos. En este estudio se analizó el efecto de una mezcla comercial de microorganismos eficientes (EM) (Rhodopseudomonas palustris, Lactobacillus plantarum, Lactobacillus casei y Saccharomyces cerevisiae) sobre la calidad del agua, sedimento y el crecimiento en un cultivo intensivo de camarón L. vannamei. La evaluación consistió en tres tratamientos: i) estanques sin EM (C), ii) estanques con dosis de 4L/ha (EM1) y iii) estanques con dosis de 10L/ha (EM2). Los resultados demostraron menor tiempo de cosecha en los tratamientos EM1 (90d) y EM2 (105d). Los tratamientos EM1 y EM2 mantuvieron significativamente regulados los valores del pH (EM1, 8.03±0.33; EM2, 7.77±0.22) y redujeron las concentraciones de nitrato (EM1, 0.64±0.25mg/L; EM2, 0.39±0.26mg/L). El tratamiento EM2 presentó la mayor remoción de materia orgánica (1.77±0.45%). El tratamiento EM1 mejoró la TCE (2.69±0.35%/d) y FCA (1.46±0.20). Los tratamientos EM1 y EM2 presentaron mayor supervivencia con 61±8.76% y 60±10.5%, respectivamente. Este estudio demostró el efecto benéfico del uso de la mezcla comercial en los parámetros ambientales y de crecimiento en un cultivo intensivo de L. vannamei.

Faunistic analysis of the caridean shrimps inhabiting seagrasses along the NW coast of the Gulf of Mexico and Caribbean Sea

Seagrass meadows are highly productive and ecologically important habitats in estuaries and coastal lagoons, and contain a variety of faunal communities, from which the caridean shrimps are a dominant component. The purpose of this work was to analyze the environmental parameters of water and sediments, with the biological components in seagrass epifaunal communities, from the Western Gulf of Mexico and the Caribbean Sea. For this, density and diversity of caridean shrimps were analyzed and correlated with environmental parameters and seagrass biomass, and zoogeographic affinities were determined. The spatial distribution of caridean shrimps was recorded for 12 localities with Halodule wrightii and Thalassia testudinum monospecific seagrass meadows. A total of 72 158 individuals of 16 taxa were collected. Among results, the Hippolytidae resulted the most abundant group (92.3%) with eight species, and was followed by Palaemonidae with 7.6% of the abundance and seven species, and the Alpheidae with only one genus. From the total of collected carideans, a 37.3% was found in H. wrightii and 62.7% in T. testudinum. The dominant species were Hippolyte zostericola (12.39ind./m2), Tozeuma carolinense (9.5ind./m2), Thor dobkini (4.84ind./m2) and Palaemonetes vulgaris (4.87ind./m2). The zoogeographic distribution of the carideans presented two groups: species of the Virginian-Carolinean province representing its Southern limit (43.75%) and species of the Brazilian-Caribbean province representing its Northern limit (56.25%). The species H. zostericola, T. carolinense, P. vulgaris, P. pugio and P. intermedius are widely distributed along the Western Atlantic coast. This study has base line information for seagrass habitats, the community of epifaunal carideans and their ecological affinities, previous to the oil spill in the Gulf of Mexico.

Las praderas de pastos marinos son hábitats altamente productivos y ecológicamente importantes a lo largo de las costas y estuarios, en estas se encuentra una gran variedad de comunidades faunísticas, donde los camarones carideos son un componente dominante por su densidad. Los parámetros ambientales del agua y sedimento y los componentes biológicos de biomasa de pastos marinos y comunidad epifaunística fueron recolectados a lo largo del occidente del Golfo de México y Mar Caribe. La densidady diversidad de los camarones carideos fueron analizadas y correlacionadas con los parámetros ambientales y biomasa de pastos, también se determinaron las afinidades zoogeográficas de las especies. La distribución espacial de los camarones carideos fue registrada en 12 localidades con praderas monoespecíficas de los pastos Halodule wrightii y Thalassia testudinum. Un total de 72 158 individuos pertenecientes a 16 taxa fueron recolectados. La familia Hippolytidae incluyó a ocho especies y representó el 92.3% de la abundancia, la familia Palaemonidae comprendió a siete especies y el 7.6%, y la familia Alpheidae estuvo representada por un solo género. Del total de carideos recolectados, el 37.3% se capturó en H. wrightii y el 62.7% en T. testudinum. Las especies dominantes fueron Hippolyte zostericola (12.39ind./m2), Tozeuma carolinense (9.5ind./m2), Thor dobkini (4.84ind./m2) y Palaemonetes vulgaris (4.87ind./m2). La composición zoogeográfica de los carideos estudiados estuvo representada por dos grupos: el primero constituido por especies afín a la provincia Virginiana- Carolineana en su límite más sureño (43.75%), y el segundo por especies de la provincia Brasileña-Caribeña con su límite más norteño (56.25%). Las especies H. zostericola, T. carolinense, P. vulgaris, P. pugio y P. intermedius tienen una amplia distribución a lo largo de la costa noreste Atlántica. Este estudio constituye la línea base de información sobre los hábitats de pastos marinos, la comunidad de camarones carideos epifaunales y sus afinidades ecológicas de recolectas previas al derrame de petróleo en el noreste del Golfo de México.

[Ichthyofauna from wetlands of San Pedro, Balancán, Tabasco, México]. / Ictiofauna de los humedales del río San Pedro, Balancán, Tabasco, México.

San Pedro River's wetlands sustain trophic nets in the fluvial system, due to the high habitat availability, and space and temporal variations. In order to describe the relationship between environmental parameters and ichthyofauna, this study evaluated fish assemblages composition, distribution, abundance, density, biomass, richness species, diversity and equitability in the wetlands. Sampling considered three different sites and climatic seasons (dry, rainy and cold fronts). The physical and chemical parameters considered were dissolved oxygen, temperature, pH, water transparency and the depth. Fishes were caught with a shrimp net, after six minutes towings and were identified afterwards. A total of 1 049 organisms of 25 fish species were caught, two of which were exotic species: Oreochromis niloticus and Parachromis managuense. A total of 23 species were found at site I (with the highest density 0.23 ind./m2), 17 at site II (0.23 ind./m2) and 14 at site III (0.12 ind./m2). The dry season had the highest species number with 21 species, followed by the rainy season with 17 species, and the cold season with five species. Similarly, the highest biomass (8.30 g/m2) was found in dry season, followed by the rainy (2.16 g/m2) and the cold seasons (0.03 g/m2). Considering seasons, highest density was found during the dry (0.436 ind./m2), followed by the rainy (0.213 ind./m2) and the cold (0.023 ind./m2) seasons. The dominant density species during the study period, according to the quadrants graphic of Olmstead-Tukey were: Petenia splendida, Vieja heterospila, Vieja synspila, Dorosoma petenense and Astyanax aeneus. There were significant differences in the species richness among sites. Temperature, depth and transparency showed differences among the seasons. The canonical correspondence analysis indicated that fish distribution was governed by environmental parameters during all seasons. In terms of fish abundance and composition, environmental parameters play an important role showing spatial and temporal differences in the ecosystem, this could be explained with the fact that most of young fishes have a movement behavior to the wetlands, searching refuge and feed during the dry season. Considering the diversity indexes variation, it may be concluded that San Pedro River's wetlands correspond to a system where the ichthyofauna composition fluctuates spatial and seasonally.

Ictiofauna de los humedales del río San Pedro, Balancán, Tabasco, México

Ichthyofauna from wetlands of San Pedro, Balancán, Tabasco, México. San Pedro River’s wetlands sustain trophic nets in the fluvial system, due to the high habitat availability, and space and temporal variations. In order to describe the relationship between environmental parameters and ichthyofauna, this study evaluated fish assemblages composition, distribution, abundance, density, biomass, richness species, diversity and equitability in the wetlands. Sampling considered three different sites and climatic seasons (dry, rainy and cold fronts). The physical and chemical parameters considered were dissolved oxygen, temperature, pH, water transparency and the depth. Fishes were caught with a shrimp net, after six minutes towings and were identified afterwards. A total of 1 049 organisms of 25 fish species were caught, two of which were exotic species: Oreochromis niloticus and Parachromis managuense. A total of 23 species were found at site I (with the highest density 0.23ind./m²), 17 at site II (0.23ind./m²) and 14 at site III (0.12ind./m²). The dry season had the highest species number with 21 species, followed by the rainy season with 17 species, and the cold season with five species. Similarly, the highest biomass (8.30g/m²) was found in dry season, followed by the rainy (2.16g/m²) and the cold seasons (0.03g/m²). Considering seasons, highest density was found during the dry (0.436ind./m²), followed by the rainy (0.213ind./m²) and the cold (0.023ind./m²) seasons. The dominant density species during the study period, according to the quadrants graphic of Olmstead-Tukey were: Petenia splendida, Vieja heterospila, Vieja synspila, Dorosoma petenense and Astyanax aeneus. There were significant differences in the species richness among sites. Temperature, depth and transparency showed differences among the seasons. The canonical correspondence analysis indicated that fish distribution was governed by environmental parameters during all seasons. In terms of fish abundance and composition, environmental parameters play an important role showing spatial and temporal differences in the ecosystem, this could be explained with the fact that most of young fishes have a movement behavior to the wetlands, searching refuge and feed during the dry season. Considering the diversity indexes variation, it may be concluded that San Pedro River’s wetlands correspond to a system where the ichthyofauna composition fluctuates spatial and seasonally. Rev. Biol. Trop. 59 (2): 693-708. Epub 2011 June 01.

Los humedales de San Pedro sostienen redes tróficas del sistema fluvial debido a la alta disponibilidad de hábitats y a sus variaciones espacio-temporales. En esta investigación se estudió la composición, densidad y biomasa de la ictiofauna de los humedales; se capturaron 1 049 organismos de 25 especies, dos son exóticas: Oreochromis niloticus y Parachromis managuense. Con 23 especies capturadas en el sitio I, 17 en el II y 14 en el III. En la época de secas se obtuvo mayor riqueza con 21 especies, lluvias con 17 y cinco en nortes. La mayor densidad se mostró en el sitio II (0.23ind./m²), seguido de los sitios I y III (0.12, 0.12ind./m²). La mayor biomasa fue en secas (8.30g/m²), seguida de lluvias (2.1g/m²) y por último nortes (0.01g/m²). La mayor densidad se mostró en secas (0.43ind./m²) y la mínima en nortes (0.023ind./m²). Las especies dominantes en densidad según el diagrama Olmstead-Tukey fueron: Petenia splendida, Vieja heterospila, Vieja synspila, Dorosoma petenense y Astyanax aeneus. Por lo tanto, existieron diferencias significativas en los parámetros ecológicos y ambientales. Al considerar la variación en la riqueza podemos concluir que los humedales del río San Pedro, es un sistema donde la composición de la ictiofauna responde a las fluctuaciones espaciales y temporales.

Caracterización espacio-temporal del hábitat y presencia de Dermatemys mawii (Testudines: Dermatemydidae) en la cuenca del Grijalva-Usumacinta, Tabasco, México

Presence and spatio-temporal habitat characterization of Dermatemys mawii (Testudines: Dermatemydidae) in the Grijalva-Usumacinta watershed, Tabasco, Mexico. The Central American River Turtle (Dermatemys mawii) is an endangered species that has been poorly studied. There are no reports on their population status, habitat condition, and the species distribution area is still unknown. This study analyzes the seasonal and spatial variations of their habitat and the presence/absence of D. mawii in three rivers within the Pantanos de Centla Biosphere Reserve (Tabasco, Mexico). For habitat characterization, natural segmentation of rivers was used and three sites per segment were identified, 9 in each rivers (Grijalva and Usumacinta) and 6 in Tabasquillo. Additionally, the evaluation of 11 environmental variables such as water hydrological, physicochemical characteristics and riparian and hydrophytic vegetation were carried out during two different seasons (dry and rainy). The presence/absence of species was assessed with eight fike nets that were set per segment, with a capture effort of 384 hours per trap. The capture per unit effort (CPUE) was used as an indicator of relative abundance. The results indicated spatio-temporal variations in habitat characteristics and the presence of environmental gradients. The principal components analysis (PCA) applied allowed us to determine that the first three components explained 67.8% of the environmental variability. The species presence was confirmed in all rivers, however significant differences exists in their relative abundance: the highest was registered in the Tabasquillo River where the species was present in both seasons and in all segments. Of the 11 environmental variables analyzed, the gradient, shelter and depth were the most indicative of species presence. The obtained results evidenced the importance of riparian vegetation as habitat for Dermatemys. This represents the first approach towards an action plan for a species and its habitat protection within the Pantanos de Centla Biosphere Reserve. Rev. Biol. Trop. 58 (4): 1247-1260. Epub 2010 December 01.

La tortuga centroamericana (Dermatemys mawii) es una especie en peligro de extinción pobremente estudiada. En el presente trabajo se analizaron las variaciones estacionales y espaciales del hábitat y se relacionaron con la presencia/ausencia de D. mawii en tres ríos de la Reserva de la Biosfera Pantanos de Centla (Tabasco, México). Para caracterizar el hábitat se evaluaron 11 variables (hidrológicas, fisicoquímicas del agua y de la vegetación) en dos temporadas (seca y lluviosa). Para determinar la presencia/ ausencia de la especie se colocaron 8 trampas de desvío acuáticas, empleando la captura por unidad de esfuerzo (CPUE) como indicador de la abundancia relativa. Los resultados indicaron variaciones espacio-temporales. El análisis de componentes principales (ACP) permitió determinar la variabilidad ambiental. La presencia de la especie se confirmó en los tres ríos, sin embargo la mayor abundancia relativa se registró en el Río Tabasquillo. Cuatro variables tuvieron el mayor peso como variables predictoras de la presencia de la especie. Con los resultados obtenidos, es evidente la importancia que tiene el ambiente ribereño como hábitat para Dermatemys, asimismo es posible hacer el primer acercamiento a un plan de acción para la protección de la especie y su hábitat en esta reserva.

[Presence and spatio-temporal habitat characterization of Dermatemys mawii (Testudines: Dermatemydidae) in the Grijalva-Usumacinta watershed, Tabasco, Mexico]. / Caracterización espacio-temporal del hábitat y presencia de Dermatemys mawii (Testudines: Dermatemydidae) en la cuenca del Grijalva-Usumacinta, Tabasco, México.

The Central American River Turtle (Dermatemys mawii) is an endangered species that has been poorly studied. There are no reports on their population status, habitat condition, and the species distribution area is still unknown. This study analyzes the seasonal and spatial variations of their habitat and the presence/absence of D. mawii in three rivers within the Pantanos de Centla Biosphere Reserve (Tabasco, Mexico). For habitat characterization, natural segmentation of rivers was used and three sites per segment were identified, 9 in each rivers (Grijalva and Usumacinta) and 6 in Tabasquillo. Additionally, the evaluation of 11 environmental variables such as water hydrological, physicochemical characteristics and riparian and hydrophytic vegetation were carried out during two different seasons (dry and rainy). The presence/absence of species was assessed with eight fike nets that were set per segment, with a capture effort of 384 hours per trap. The capture per unit effort (CPUE) was used as an indicator of relative abundance. The results indicated spatio-temporal variations in habitat characteristics and the presence of environmental gradients. The principal components analysis (PCA) applied allowed us to determine that the first three components explained 67.8% of the environmental variability. The species presence was confirmed in all rivers, however significant differences exists in their relative abundance: the highest was registered in the Tabasquillo River where the species was present in both seasons and in all segments. Of the 11 environmental variables analyzed, the gradient, shelter and depth were the most indicative of species presence. The obtained results evidenced the importance of riparian vegetation as habitat for Dermatemys. This represents the first approach towards an action plan for a species and its habitat protection within the Pantanos de Centla Biosphere Reserve.

Hematology and serum biochemistry comparison in wild and captive Central American river turtles (Dermatemys mawii) in Tabasco, Mexico.

Hematological and serum biochemistry analyses were determined on 51 Central American river turtles (Dermatemys mawii) during the dry and rainy seasons of 2006. Turtles came from two sites: Pantanos de Centla Biosphere Reserve and a turtle breeding farm, both located in Tabasco State, Mexico. Physical examination and body measures of animals were performed. Incidence and prevalence of hemoparasites were explored. Captive organisms were in poor physical condition while wild turtles were apparently healthy. There were differences in several hematological parameters related with the condition and the season. During the dry season captive turtles exhibited higher levels of uric acid and urea, as well as lower levels of glucose. Haemogregarina sp. was detected in 100% of the wild individuals, but not in captive individuals. Its incidence was greater during the rainy season. This is the first health assessment and hematology study of this critically endangered species.