Forest buffer-strips mitigate the negative impact of oil palm plantations on stream communities.

The global area cultivated with oil palm has doubled in the past two decades, causing deforestation, land-use change, freshwater pollution, and species loss in tropical ecosystems worldwide. Despite the palm-oil industry been linked to severe deterioration of freshwater ecosystems, most studies have focused on terrestrial environments, while freshwaters have been significantly less studied. We evaluated these impacts by contrasting freshwater macroinvertebrate communities and habitat conditions in 19 streams from primary forests (7), grazing lands (6), and oil palm plantations (6). In each stream, we measured environmental characteristics, e.g., habitat composition, canopy cover, substrate, water temperature, and water quality; and we identified and quantified the assemblage of macroinvertebrates. Streams in oil palm plantations lacking riparian forest strips showed warmer and more variable temperatures, higher turbidity, lower silica content, and poorer macroinvertebrate taxon richness than primary forests. Grazing lands showed higher conductivity and temperature, and lower dissolved oxygen and macroinvertebrate taxon richness than primary forests. In contrast, streams in oil palm plantations that conserved a riparian forest, showed a substrate composition, temperature, and canopy cover more similar to the ones in primary forests. These habitat improvements by riparian forests in the plantations increased macroinvertebrate taxon richness and maintained a community resembling more the one in primary forests. Therefore, the conversion of grazing lands (instead of primary forests) to oil palm plantations can increase freshwater taxon richness only if riparian native forests are safeguarded.

Macroinvertebrates of Eichhornia crassipes (Pontederiaceae) roots in the alluvial floodplain of large tropical rivers (Argentina)

Introduction: Eichhornia crassipes is a dominant aquatic plant of neotropical-river floodplains and is invasive in warm waters of different continents. Plants provide food and habitat for fish, especially Prochilodus lineatus and Gymnotus omarorum, which are relevant to subsistence fishing by local indigenous communities. Objective: In this study we describe the main traits of E. crassipes floating meadows, and analyze the abundance and composition of macroinvertebrate assemblages associated with their roots in two floodplain wetlands of the Paraná River (within the Ramsar site Wetlands Chaco) and of the Pilcomayo River (within the Pilcomayo River National Park). Methods: During spring and summer, the macroinvertebrates were collected in monospecific stands of E. crassipes with a net of 962 cm2 area and 500 µm mesh size. Leaf density, the biomass of leaves and roots, the length of leaves and roots, and the water quality were measured simultaneously. Results: Temperature, oxygen concentration, and nutrient content were significantly higher and electrical conductivity was lower in the Pilcomayo than in the Paraná floodplain. E. crassipes growing in the Pilcomayo floodplain had longer leaves and less root biomass than those found in the Paraná floodplain. The number of macroinvertebrates per 1 000 g root dry weight and per m2 was significantly different between both floodplains, but the taxon richness was similar. Non Metric Multidimensional Scaling analysis differentiated the abundance of 14 selected taxa between both floodplains, and showed a high correlation between the environmental variables and macroinvertebrate abundance. The most abundant taxonomic groups in the Paraná River floodplain were oligochaetes (Naididae), ostracods mainly Cytheridella ilosvayi and larvae of non-biting midges (Chironomidae). Two families, Hydrobiidae (Heleobia parchappii) and Chironomidae accounted for 49.3 % of the total abundance in the Pilcomayo floodplain. The prawns Macrobrachium jelskii and M. amazonicum, frequent in the Pilcomayo floodplain, were not found in the Paraná floodplain. Conclusions: The different environmental conditions in both floodplains affect the abundance, composition, and the dominance of macroinvertebrate assemblages; however, the total taxa richness was similar. The area occupied by E. crassipes in the floodplains of these rivers provides the habitat that contributes most to overall biotic diversity, which must be considered in management strategies.

Introduccion: Eichhornia crassipes es la planta acuática dominante en la planicie de inundación de los ríos tropicales y ha invadido las aguas cálidas de diferentes continentes. Las plantas proveen alimento y hábitat para los peces, especialmente Prochilodus linneatus y Gymnotus omarorum, que son relevantes para la pesca de subsistencia de las comunidades indígenas locales. Objetivo: En el presente trabajo nosotros describimos las principales características de las formaciones flotantes de E. crassipes, y analizamos la abundancia y composición de los ensambles de macroinvertebrados asociados a sus raíces en dos humedales de las planicies de inundación de los ríos Paraná (dentro del sitio Ramsar Humedales Chaco) y Pilcomayo (dentro del Parque Nacional Río Pilcomayo). Métodos: Durante la primavera y el verano, los macroinvertebrados se recolectaron en formaciones monoespecíficas de E. crassipes con una red de 962 cm2 y 500 µm de tamaño de malla. La densidad de hojas, la biomasa de hojas y raíces, la longitud de las hojas y raíces y la calidad del agua se midieron simultáneamente. Resultados: La temperatura, la concentración de oxígeno disuelto y el contenido de nutrientes fueron significativamente mayores y la conductividad eléctrica fue significativamente menor en la planicie de inundación del Pilcomayo que en la del Paraná. Las plantas de E. crassipes que crecen en la planicie de inundación del Pilcomayo tuvieron hojas más largas y menos biomasa de raíces que las encontradas en la planicie del Paraná. El número de macroinvertebrados por 1 000 g. de peso seco de la raíz y por m2 fueron significativamente diferentes entre ambas planicies de inundación, pero la riqueza de taxa fue similar. El análisis de Escalamiento Multidimensional No Métrico diferenció la abundancia de los 14 taxa seleccionados entre ambas planicies de inundación, y mostró alta correlación entre las variables ambientales y la abundancia de los macroinvetebrados. Los grupos taxonómicos más abundantes en la planicie de inundación del río Paraná fueron los oligoquetos (Naididae), los ostrácodos, principalmente Cytheridella ilosvayi y las larvas de mosquitos no picadores (Chironomidae). Dos familias, Hydrobiidae (Heleobia parchappii) y Chironomidae representaron el 49,3 % de la abundancia total en la planicie de inundación del Pilcomayo. Los camarones Macrobrachium jelskii y M. amazonicum, frecuentes en la planicie de inundación del Pilcomayo, no se encontraron en la planicie de inundación del Paraná. Conclusiones: Las diferentes condiciones ambientales en ambas planicies de inundación afectan la abundancia, composición y la dominancia de los ensambles de macroinvertebrados; sin embargo, la riqueza total de taxa fue similar. El área ocupada por E. crassipes en la planicie de inundación de estos ríos proporciona el hábitat que más contribuye a la diversidad biótica, lo que debe ser considerado en las estrategias de manejo.

Intensive removal of signal crayfish (Pacifastacus leniusculus) from rivers increases numbers and taxon richness of macroinvertebrate species.

Invasive species are a major cause of species extinction in freshwater ecosystems, and crayfish species are particularly pervasive. The invasive American signal crayfish Pacifastacus leniusculus has impacts over a range of trophic levels, but particularly on benthic aquatic macroinvertebrates. Our study examined the effect on the macroinvertebrate community of removal trapping of signal crayfish from UK rivers. Crayfish were intensively trapped and removed from two tributaries of the River Thames to test the hypothesis that lowering signal crayfish densities would result in increases in macroinvertebrate numbers and taxon richness. We removed 6181 crayfish over four sessions, resulting in crayfish densities that decreased toward the center of the removal sections. Conversely in control sections (where crayfish were trapped and returned), crayfish density increased toward the center of the section. Macroinvertebrate numbers and taxon richness were inversely correlated with crayfish densities. Multivariate analysis of the abundance of each taxon yielded similar results and indicated that crayfish removals had positive impacts on macroinvertebrate numbers and taxon richness but did not alter the composition of the wider macroinvertebrate community. Synthesis and applications: Our results demonstrate that non-eradication-oriented crayfish removal programmes may lead to increases in the total number of macroinvertebrates living in the benthos. This represents the first evidence that removing signal crayfish from riparian systems, at intensities feasible during control attempts or commercial crayfishing, may be beneficial for a range of sympatric aquatic macroinvertebrates.