Abstract
The development of effective monitoring tools depends on finding sensitive metrics that are capable of detecting the most important environmental impacts at a given region. We assessed if metrics derived from stream fish assemblages reflect physical habitat degradation and changes in land cover. We sampled the ichthyofauna and environmental characteristics of 16 stream sites of first and second order in the Upper Tocantins River basin. The streams were classified according to their environmental characteristics into reference (n = 5), intermediate (n = 4), and impacted (n = 7). A total of 4,079 individuals in five orders, 12 families, and 30 species were collected. Of the 20 metrics tested, eight were non-collinear and were tested for their performance in discriminating among groups of streams. Three metrics were sensitive to the gradient of degradation: Berger-Parker dominance index, percentage of characiform fish, and percentage of rheophilic individuals. Some commonly used metrics did not reflect the disturbances and many others were redundant with those that did. These results indicate that the metrics derived from fish assemblages may be informative for identifying the conservation status of streams, with the potential to be used in biomonitoring.
Highlights
Anthropogenic impacts, such as pollution, riparian zone logging, and landscape fragmentation (Barletta et al 2010, Naiman and Dudgeon 2011) affect aquatic ecosystems almost everywhere
We evaluated whether metrics based on fish assemblages can be used to differentiate streams according to their conservation status
We described fish assemblage of headwater sites in relation to potential indicators and tested whether these data would allow us to distinguish among streams with different levels of environmental degradation
Summary
Anthropogenic impacts, such as pollution, riparian zone logging, and landscape (including network) fragmentation (Barletta et al 2010, Naiman and Dudgeon 2011) affect aquatic ecosystems almost everywhere. These impacts have negatively influenced the chemical, physical, and biological integrity of ecosystems (Barletta et al 2010, Casatti et al 2009). It has been suggested that curves of relative abundances and biomass allow the assessment of the level of disturbance in an environment (Clarke and Warwick 2001). The number of species, the presence of rare species, and the distribution of the abundance of individuals among species (evenness) in an assemblage are potentially informative metrics for the differentiation of assemblages that have been subjected to different levels of disturbance (Barman and Gupta 2015)
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