Effects of multiple stressors associated with agriculture on stream macroinvertebrate communities in a tropical catchment

Abstract

Tropical forests are declining at unprecedented rates in favour of agriculture, and streams can be severely impacted due to effects of multiple stressors that have rarely been considered together in tropical studies. We studied the effects of multiple stressors associated with agricultural practices (pesticide toxicity, nutrient enrichment and habitat alteration–quantified as TU max , soluble reactive phosphorus concentration and sedimentation, respectively) on macroinvertebrate communities in a tropical catchment in Panama (13 stream sites sampled in 20 occasions from 2015 to 2017, with 260 samples in total). We examined how macroinvertebrate abundance, taxonomic richness, community composition and biotic indices (SPEAR and BMWP/PAN, which were specifically designed to detect pesticide toxicity and nutrient enrichment, respectively) varied depending on the studied stressors, considering their single and combined effects. Our analyses revealed significant effects of the studied stressors on macroinvertebrate communities, with two particular results that merit further attention: (1) the fact that pesticide toxicity affected BMWP/PAN, but not SPEAR, possibly because the former had been adapted for local fauna; and (2) that most stressors showed antagonistic interactions (i.e., lower combined effects than expected from their individual effects). These results highlight the need for toxicity bioassays with tropical species that allow adaptations of biotic indices, and of observational and manipulative studies exploring the combined effects of multiple stressors on tropical macroinvertebrate communities and ecosystems, in order to predict and manage future anthropogenic impacts on tropical streams.

Hidden biodiversity in Neotropical streams: DNA barcoding uncovers high endemicity of freshwater macroinvertebrates at small spatial scales

“…In addition, our rarefaction/extrapolation approach showed that this diversity is still under-sampled across sites both within the PCW and along the Isthmus of Panama (Fig 3). These findings confirm that the diversity of freshwater macroinvertebrates in Neotropical environments is largely under-studied [33,69,70], and could be much higher than previously thought. In particular, these findings highlight the fact that there is limited published research using genetic methods to study macroinvertebrate diversity in this region.…”

“…Assessing the patterns and drivers of macroinvertebrate diversity at different scales is particularly relevant, given the increasing rate of environmental degradation in Neotropical regions [ 30 – 33 ]. This includes alterations such as introduction of alien species [ 34 , 35 ], the development of megaprojects [ 36 ], habitat degradation, water pollution, and climate change [ 30 , 33 , 37 , 38 ]⁠. As a consequence, a large portion of this biodiversity risks being lost before discovery.…”

Hidden biodiversity in Neotropical streams: DNA barcoding uncovers high endemicity of freshwater macroinvertebrates at small spatial scales

“…These findings confirm that the diversity of freshwater macroinvertebrates in Neotropical environments is largely understudied [10,34,68], and could be much higher than previously thought. In addition, the fact that only a small number of specimens from these taxa matched available sequences in public databases further highlights the potential for biodiversity discovery in Neotropical freshwater environments.…”

“…Assessing the patterns and drivers of macroinvertebrate diversity at different scales is particularly relevant, given the increasing rate of environmental degradation in Neotropical regions [31–34]. This includes alterations such as introduction of alien species [35,36], habitat degradation, water pollution, and climate change [31,34,37,38]□. In consequence, a large portion of this biodiversity risks being lost before discovery.…”

A common fungicide impairs stream ecosystem functioning through effects on aquatic hyphomycetes and detritivorous caddisflies

“…We addressed research gaps in a microcosm experiment, where we examined the effects of chlorothalonil (a common fungicide in agriculture and forestry worldwide; e.g., Du Gas et al, 2017;Cornejo et al, 2019) on microbial and invertebrate-mediated decomposition of litter of several riparian plant species, individually and mixed. We used a common detritivorous caddisfly and quantified its survival and growth, and we determined AH sporulation rate, taxon richness and assemblage composition, in response to (1) litter pre-treated with the fungicide, (2) waterborne fungicide, and (3) both exposure modes simultaneously.…”