Abundance Of Invertebrate Taxa Research Articles

Influence of leaf miners and environmental quality on litter breakdown in tropical headwater streams

Headwater streams subjected to anthropogenic impacts are prone to environmental quality decay, which may affect stream functioning. To investigate the effects of loss of environmental quality in stream functioning, we tested the hypothesis that leaf breakdown is faster in streams with higher environmental quality, and that invertebrate community structure and microbial biomass are negatively affected by habitat simplification resulting from environmental degradation. We submerged Alchornea glandulosa leaves in litter bags in nine streams, in Southern Brazil, in an environmental gradient. We characterized breakdown rates (k), physical in-stream characteristics, abundance of invertebrate taxa, and functional groups and microbial biomass for each stream, with three mesh exclusions (fine, medium, coarse). Breakdown was faster in the most preserved stream (k = − 0.032 ± 0.005) and decreased towards the most disturbed stream (k = − 0.0034 ± 0.001). Breakdown rates were positively associated with underwater habitat complexity, equitability of macroinvertebrate taxa, and abundance of Stenochironomus sp., which together explained 51% of breakdown rate variability. Breakdown rates from the less disturbed streams (n = 7, excluding urban-influenced) were lowest in medium-mesh, intermediate in fine-mesh, and highest in coarse-mesh bags, and the only taxon that differed according to this pattern was the mining-chironomid Stenochironomus sp., which suggests that this taxon had a significant activity of leaf processing.

Selective predation by reintroduced juvenile Lake sturgeon (Acipenser fulvescens) in Ft. Loudoun reservoir, Tennessee (USA)

Following water quality and minimum flow improvements to the impounded Tennessee and Cumberland Rivers, juvenile lake sturgeon (Acipenser fulvescens) have been restocked annually since 2000. Our goal was to seasonally assess foraging mode of this recovering population in Ft. Loudoun Reservoir in the Upper Tennessee River. During 2014–15, individuals were captured using trot-lines in a 13-km reach that supports the greatest density of lake sturgeon. We used colonic flushing and gastric lavage techniques to obtain diet. We took systematic benthic sediment grabs along multiple transects throughout the reach and opportunistically deployed rock cages filled with hard substrates to assess potential prey that colonize hard surfaces. Foraging modes of lake sturgeon were determined by comparing relative abundances of invertebrate taxa in the gut contents (6581 invertebrates) of 28 fish to the relative abundances of the same invertebrate taxa collected from the resource base (1667 invertebrates). Proportional similarity, Levin’s niche breadth, and Manly’s index were used to assess the degree of prey selectivity. Lake sturgeon fed selectively on a narrow range of available prey consisting mostly of larval chironomids (93% composition by number during warm season, 96% during cool season), some genera of which they prey upon selectively, primarily Chironomus sp., but to a lesser extent Procladius, Ablabesmyia, Coelotanypus, and Cryptochironomus spp. Meanwhile, other abundant taxa in the resource base were avoided, such as Oligochaetes, Hexagenia mayflies, and the chironomid Glyptotendipes. Our results illustrate that assessing seasonally available prey from habitat utilized by lake sturgeon is important when investigating diet preference.

Reference scenarios for exposure to plant protection products and invertebrate communities in stream mesocosms

Higher tier aquatic risk assessment for plant protection products (PPPs) is often based on pond-like mesocosm studies in which transient and dynamic PPP exposure scenarios as observed in lotic systems are hardly achievable. Thus, the present study presents dynamic PPP exposure scenarios at different time scales under flow-through conditions as typical for streams in agricultural landscapes. The stream mesocosm setup allows testing the influence of spatial gradients of exposure over the length of the mesocosms. The use of the fluorescent tracer uranine revealed the hydraulic processes generally underlying peak- and hour-scale exposure scenarios and demonstrated an optimized application technique to achieve stable day-scale exposures. Furthermore, to account for potential reactions of invertebrates to PPP exposures in streams (e.g. avoidance behavior and drift), the present study thus aimed at a comprehensive evaluation on how PPP exposure and the establishment of invertebrates can be advanced within stream mesocosm testing. For both, peak- and hour-scale exposure as well as the experiments considering the establishment of invertebrates, the presented compilation of experiments was able to highlight the influence of aquatic macrophytes within stream mesocosms. Since the field relevance of the higher tier aquatic risk assessment for PPPs relies qualitatively on the presence of potentially sensitive or vulnerable species, those species were especially considered. Thus, the establishment of aquatic invertebrates in non-dosed streams was evaluated with respect to (i) the presence of different aquatic macrophytes and (ii) the duration of the pre-experimental period. The present study highlights the beneficial influence of complex-structured macrophytes and prolonged pre-experimental periods on the abundance of invertebrate taxa. Furthermore, population dynamics were evaluated statistically by simulating PPP-related declines of 30, 50 and 70%. Thereby, minimum detectable difference (MDD) classes of mostly ≥III were found for 12 out of 15 taxa for at least two consecutive sampling dates.

Bioturbation by a dominant detritivore in a headwater stream: litter excavation and effects on community structure

Bioturbation can affect community structure by influencing resource distribution and habitat heterogeneity. Bioturbation by detritivores in small headwater streams could affect community structure by reintroducing buried detrital resources into the food web and could also affect the distribution of various taxa on detritus. We evaluated the ability of the caddisfly Pycnopsyche gentilis to uncover experimentally buried leaves in a headwater stream. Packs of leaves were placed in enclosures and covered with a known volume of sediment. We added 0, 3 or 6 large Pycnopsyche to the enclosures which were permeable to most other invertebrate taxa. Leaf packs were sampled after 23 days and leaf pack mass, the amount of sediment covering the leaf packs, and macro- and microinvertebrate densities on leaf packs were quantified. There was a significant negative relationship between Pycnopsyche density and leaf pack mass. Pycnopsyche also reduced the volume of sediment covering leaf packs. Pycnopsyche had complex effects on the abundance of invertebrate taxa associated with the leaves. Some taxa exhibited their highest abundance in the 3 Pycnopsyche treatment while others exhibited non-significant increases as Pycnopsyche density increased. These results suggest that the beneficial effects of Pycnopsyche (e.g. uncovering leaves which increases the availability of habitat and food) outweigh any negative effects (e.g. disturbance, encounter competition) of the caddisfly when it is present at lower densities. However, the negative impacts of Pycnopsyche appear to outweigh the positive effects via sediment removal at higher caddisfly densities for some taxa. Our results suggest that bioturbating organisms in streams have the potential to reintroduce organic matter to detrital food webs and affect the distribution and abundance of benthic taxa associated with organic matter.

Effects of discharges from the textile industry on the biotic integrity of benthic assemblages

We explored the effects of a textile industry effluent on water quality, habitat quality and structural and functional responses of benthic communities in a lowland stream. Two sampling sites were selected: site 1 was located 300 m upstream of the outflow from the textile factory and site 2 was 500 m downstream from the discharge point. Samples of water, microbenthos, invertebrates and aquatic plants were taken seasonally. The effluent from the textile industry modified the structure of the microbenthic assemblages downstream, increased the density of organisms and the biomass of primary producers, but diminished the species richness. The oxygen consumption of the microbenthic community was 3× higher downstream of the effluent and abnormal frustules of diatoms were noticed. The richness and abundance of invertebrate taxa were lower at the impacted site. The invertebrate modes of existence and the functional feeding groups were also significantly affected. This study is an important baseline for assessment of lowland streams with high water residence time and a notable development of hydrophytes. It will also provide a baseline for the monitoring and restoration, or remediation, programs using the metrics of biotic integrity, particularly in South American countries where such metrics are rarely employed.

Limited effects of grazer exclusion on the epiphytes of Posidonia sinuosa in South Australia

The role of grazing in regulating the abundance and biomass of epiphytes of the seagrass Posidonia sinuosa Cambridge et Kuo was investigated at an oligotrophic site in lower Spencer Gulf, South Australia. Prosobranch gastropods >7 mm in size were excluded from 0.25 m 2 plots of seagrass for 3 months with four steel mesh cages, compared with four partial cages used to control for cage artefacts, and also four uncaged control plots. Abundances of epiphytic algae, invertebrates and epiphytic mass (DW, AFDW and calcium carbonate) were recorded regularly. The indirect effect of grazer exclusion on seagrass leaf mortality (necrosis) was also measured. Grazing effects on the epiphytic assemblage were detected despite some cage artefacts. Filamentous algal abundance and epiphytic biomass (AFDW) increased in response to grazer exclusion. Caging per se reduced crustose coralline algal cover and calcium carbonate during the experimental period but, after 3 months, no artefact or treatment effect was discernible. Abundances of invertebrate taxa were little affected by grazer exclusion although caging per se reduced the density of spirorbid polychaetes. Grazer exclusion did not affect seagrass necrosis. In comparison with similar studies and given the duration of exclusion, the sum of treatment effects on epiphytes and seagrass was small. Rather, the role of epiphyte grazing in this nutrient-poor area appears to be limited to the maintenance of an epiphytic assemblage that is free of filamentous algae and dominated by crustose corallines.

Invertebrate Colonization of Artificial Pondweeds of Differing Fractal Dimension

Four pondweed designs were made, using fractal dimension as a measure of complexity to obtain some a priori control of the habitat architecture. Weed designs differed in complexity but total surface area of each of the shapes was the same. Recent theory suggests that abundance of invertebrate taxa and individuals will increase with increasing fractal complexity. Invertebrate colonization of the design was followed in two trials, firstly all four weed designs together in the same pond, secondly two of the designs in separate pools. In the first trial total numbers of individuals, total taxa and numbers of several species increased markedly with increased design complexity. in the second trial colonization of pools by the larvae of a Cyphon sp. (Coleoptera) was monitored in detail. Significantly higher numbers were found on the more complex weed design. Results generally support the hypothesis, though erratic colonization of pools was also important.

Impact of farm waste on freshwater invertebrate abundance and the feeding rate of Gammarus pulex L.

Farm slurry is an important contaminant of rural catchments in the U.K., causing both major pollution incidents and more subtle chronic effects. An ecological and ecotoxicological assessment of contaminated (Clarbeston Stream) and uncontaminated (Deepford Brook) river stations revealed significant differences in the abundance of invertebrate taxa and sublethal effects on the amphipod Gammarus pulex. Fewer Leuctridae, Rhyacophilidae, Limnephilidae, Limnius volckmari, Elmis aenaea, Potamopyrgus jenkinsi and G. pulex were found in the contaminated stream and the feeding rate of caged G. pulex was also reduced. There was no significant reduction in either macroinvertebrate abundance or G. pulex feeding rate below the confluence of the contaminated and uncontaminated streams.

The effects of road and bridge construction on the bank-root macrobenthic invertebrates of a Southern Nigerian stream

A comparative study was conducted at three stations on a fourth order Nigerian stream to evaluate the effects of a road and bridge construction on the macrobenthic invertebrates of the bank-root biotope. Siltation and sedimentation appear to be the important factors affecting macroinvertebrates. At station 2, the construction site, there was a considerable reduction in the occurrence and abundance of invertebrate taxa; different groups of invertebrates showed varying responses to perturbational stress; the taxa richness, general diversity and evenness were also low. Irregular fluctuations in diversity and evenness suggested that the benthic community of station 2 was less stable than those of upstream and downstream stations. The concentrated dominance of Ephemeroptera and Coleoptera at station 2, despite low diversity, reflected the ability of a few tolerant taxa to occur there in high abundance. Faunal comparisons of the three stations confirmed the perturbational stress caused by construction activities.