Challenges Using Extrapolated Family-level Macroinvertebrate Metrics in Moderately Disturbed Tropical Streams: a Case-study From Belize

Family-level biotic metrics were originally designed to rapidly assess gross organic pollution effects, but came to be regarded as general measures of stream degradation. Improvements in water quality in developed countries have reignited debate about the limitations of family-level taxonomy to detect subtle change, and is resulting in a shift back towards generic and species-level analysis to assess smaller effects. Although the scale of pollution characterizing past condition of streams in developed countries persists in many developing regions, some areas are still considered to be only moderately disturbed. We sampled streams in Belize to investigate the ability of family-level macroinvertebrate metrics to detect change in stream catchments where less than 30% of forest had been cleared. Where disturbance did not co-vary with natural gradients of change, and in areas characterized by low intensity activities, none of the metrics tested detected significant change, despite evidence of environmental impacts. We highlight the need for further research to clarify the response of metrics to disturbance over a broader study area that allows replication for confounding sources of natural variation. We also recommend research to develop more detailed understanding of the taxonomy and ecology of Neotropical macroinvertebrates to improve the robustness of metric use

Initial development of a multi-metric index based on aquatic macroinvertebrates to assess streams condition in the Upper Isiboro-Secure Basin, Bolivian Amazon

We developed a preliminary macroinvertebrate-based multi-metric index to assess streams biotic condition in the Upper Isiboro-Secure basin (Bolivia). To do so we used eight local habitat descriptors and twelve metrics describing the structure and function of macroinvertebrate assemblages from 38 reference and 29 disturbed sites. Stepwise multiple linear regression procedures were first applied using the reference data to elaborate models describing metrics response to natural environmental in the absence of any significant disturbance. In a second step we used residuals distribution of each of the twelve models to select the most effective metrics in discriminating between reference and disturbed sites. These metrics were: number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT), abundance of EPT, relative abundance of EPT, abundance of Chironomidae and relative abundance of Chironomidae. Finally, after converting residual values of these 5 remaining metrics into probabilities, we added values to obtain a final index score and interpreted this score as excellent, good, moderate, poor or very poor. Our final multi-metric index distinguished well between natural and human-induced variation in biological condition and showed a significant negative response to a gradient of disturbances. This type of approach could be used in the near future to develop a nation wide index by increasing regional-scale monitoring

Dynamiques spatio-temporelles des déplacements de la truite fario aux stades de vie différentes. Une étude pluriannuelle dans un cours d'eau de tête de bassin versant

International audienceBrown trout (Salmo trutta) is an emblematic European fish species living primarily in well-oxygenated cool streams. As for other salmonids, reproductive migrations of mature trout individuals are well known, but also diel and seasonal movements of earlier life stages have been repeatedly reported. It suggests that the species may be sensitive to the degree of functional connectivity of streams throughout its life-cycle and this potentially at different spatio-temporal scales. Moreover, in upstream areas, where trout most frequently occur, populations are often confronted with hydropower-related alteration of stream continuity through presence of dams, weirs or water flow diversion. While observations of movement through stream networks have been regularly documented for brown trout, many questions remain open. What are the frequency, and spatial scale of dispersal events occurring over a year? How big is the proportion of population involved and how synchronized is migration? What are the main environmental drivers or triggers of dispersal at different life stages? Clarifying these questions is an important prerequisite for evaluating the influence of stream connectivity on trout population dynamics and taking efficient measures for preserving the species. We present results of a multi-annual field study, conducted on the Neste d'Oueil, a second-order mountain stream with natural hydrological regime located in the French Pyrenees. About 1900 juvenile and adult trout individuals were marked with pit-tags between 2014 and 2017. Our study design included recordings of fish movements by three fixed antennae combined with regular mobile antennae surveys at two spatial scales: 500 m (monthly) and 1.5 km (yearly). Together with yearly population electrofishing sampling providing biometric data, this resulted in a highly complementary data set, well resolved both in space and time. We use these data to analyze phenology, trajectories, extent and direction of movement, make quantitative estimates of home range extents and explore dispersal behavior types for different life stages, in particular, juvenile trout. We analyze the relationship of these patterns to temperature and discharge as well as mesohabitat and obstacle distribution within the study area. Finally we discuss the results of this work in the light of population persistence in streams but also in the perspective of improvement of stream connectivity for the species

Longitudinal and altitudinal changes of macroinvertebrate functional feeding groups in neotropical streams : a test of the River Continuum Concept

The River Continuum Concept (RCC) explains the structural and functional characteristics of stream communities focusing on the gradually changing physical components from headwaters to downstream habitats of streams and rivers. The global value of the RCC is still uncertain, possibly because physical factors (e.g., altitude and then temperature, stream order, channel width) can vary differently in longitudinal river axes across the world. Moreover, RCC predictions in relation to different physical factors have not been tested adequately in different biomes, especially biomes outside of temperate North America. Here, we report on the functional structure of macroinvertebrate communities in neotropical streams from Bolivia along a broad altitudinal gradient (from 1120 to 4300 m a.s.l.), aiming to understand how altitude can affect the longitudinal changes in functional feeding groups (FFG) and richness predicted by the RCC. The RCC predictions for functional structure were not completely matched when analyzing FFGs in relation to an index of longitudinal stream gradient. However, after removing the effect of altitude by using residuals from regressions between FFGs and altitude, FFG patterns matched RCC predictions more closely. We detected significant relationships between altitude and the relative abundance of collector-gatherers, shredders and scrapers which may be related to changes in temperature, UV radiation and canopy cover along the altitudinal gradient. Our results indicate that altitude combined with position along the longitudinal gradient is an important factor governing the FFG structure of macro invertebrate communities in neotropical streams