Revealing the pathways by which agricultural land‐use affects stream fish communities in South Brazilian grasslands

Abstract

Summary Understanding mechanisms by which agricultural practices affect freshwater ecosystems helps to inform land‐use policies and management strategies aimed at mitigating effects of agriculture on biodiversity. Land‐use activities in the catchment, riparian and local scales likely influence stream fish communities via multiple pathways, for instance, by modifying the instream habitat. We investigated the mechanisms driving local stream fish taxonomic richness and functional diversity in South Brazilian grasslands by testing a theoretical path model in which we specified a priori relationships predicting how land use at multiple scales affects instream habitat and fish communities. Agricultural activities adjacent to streams (i.e. local impact on the streambank) and catchment‐scale cropland area were positively related to macrophyte cover and negatively associated with coarse particulate organic matter (CPOM, i.e. woody debris and leaf litter). Local impact also increased substrate siltation and homogenisation. Riparian vegetation in the upstream buffer ameliorated instream habitat condition by dampening macrophyte proliferation and providing CPOM. Fish species richness increased with both macrophyte cover and CPOM, revealing multiple pathways of agricultural influence. However, functional diversity decreased only with substrate siltation, revealing a response to agricultural activities adjacent to sample sites. Agricultural streams showed a replacement of benthic and lithophilic species by a larger number of morphologically similar and macrophyte‐associated nektonic fish. Our study indicates that land‐use adjacent to streams and upstream riparian zones is critical for maintaining taxonomically and functionally diverse fish communities due to their strong effects on instream habitat. Protection and recovery of riparian zones from land‐use change can mitigate the effects of agriculture on fish communities in South Brazilian grasslands.

Metrics derived from fish assemblages as indicators of environmental degradation in Cerrado streams

“…The reference streams have well-preserved riparian forests, with a dominance of woody vegetation. These streams also have good physical integrity, with high environmental complexity, and hard substrate that maintains high species richness (Dala-Corte et al 2016). On the other hand, impacted streams have more unconsolidated substrate, which is evidence of the siltation process that is currently underway in the region (Borges et al 2015).…”

A new species of Ituglanis (Siluriformes: Trichomycteridae) from the rio Uruguai basin, southern Brazil

“…Dala-Corte et al, 2016). Thereafter, eight new specimens of I. inusitatus were captured employing the same methodology and only the smallest type-specimen (UFRGS 21242: 32.8 mm SL), identified after recognition of the new species, was collected without the help of electroshocking.…”

“…2 of Bertaco et al (2016)) with the aid of electrofishing, a method currently known for its high performance in capturing benthic species in hidden places, may explain such a recent discovery. Dala-Corte et al (2016) emphasized the importance of riparian zones in the maintenance of fish communities and recommended their protection and recovery as an attempt to mitigate the effects of agriculture in South Brazilian grasslands. The presence of I. inusitatus in only two of the 54 streams sampled by these authors, both with preserved riparian vegetation and without agricultural influence in the vicinities, provides additional support to this recommendation.…”

“…An updated list of freshwater fishes from Rio Grande do Sul including those ecoregions of Abell et al (2008) recognized three additional species of Ituglanis awaiting taxonomic description . One of them is known from only a few specimens discovered after a large collection effort in streams across the South Brazilian grasslands (see Dala-Corte et al, 2016) and is described herein.…”

Determining the relative importance of catchment- and site-scale factors in structuring fish assemblages in small coastal streams

“…Conversely, there has been an increasing focus on the impact of larger scale factors on stream ecosystems via macroecology, landscape ecology and community ecology. Some studies have revealed that agricultural land use and deforestation within catchment area influence on fish assemblages by changing habitat structure in streams (Eikaas et al, 2005;Dala-Corte et al, 2016;Molina et al, 2017). Thus, although fluvial fish assemblages are influenced by factors across scales, there is no consensus on the relative importance of site-and catchment-scale variables.…”