The Use of Littoral Benthic Macroinvertebrates of the Martín Garcia Island Nature Reserve as Indicators of Water Quality

At Martín García Island—a Natural Reserve located at the confluence of the Paraná and Uruguay rivers—we used benthic-macroinvertebrate biotic indices to elucidate the structure and community parameters of the littoral benthos and their response to environmental variables and to evaluate the island's coastal water quality. Seasonal campaigns were carried out (March/1995-March/1996) at eight sites of the island's littoral sites, selected according to the substrate characteristics (fine sands, sandy-silty, reedbed, and silty with great hydrophyte development). From the sites with a soft substrate, triplicate samples were extracted using a 225-cm2 Ekman manual dredge. The relative abundances of 71 taxa were measured: Nematoda, Turbelaria, Oligochaeta (23 sps.), Mollusca (21 sps.), Crustacea (11 sps.), Insecta (12 families), and Tardigrada. Macroinvertebrate density: 15-58,800 ind.m-2. Analysis of variance revealed significant differences between the average annual macroinvertebrate-population densities among the five sites (F: 3.059; p<0.05). Site 7 exhibited the highest density at 38,700±19,000 ind.m-2 Community parameters: diversity (H'; 0.77-2.16 bits); equitability (J; 0.16-1.02), and species richness (S; 3-29). Canonical-correspondence analysis indicated the environmental variables experiencing the greatest fluctuation to be: dissolved-oxygen concentration, pH, temperature, and conductivity. The results of this analysis suggest that macroinvertebrate-species distribution involves the physicochemical conditions of the water. Of the correlation between species and environmental variables, 95.5% were distributed on the canonical-correspondence ordering diagram's Axis 1. Functional feeding groups: In all sites and seasons, the gathering collectors predominated, followed by the scrapers, filtering collectors, shredders, and predators. Macroinvertebrate Index of Pampean-Rivers: values generally ranged from weak to weak-to-very-weak to zero pollution, but there was a high degree of pollution (2.4 and 1.5) in the spring of 1995.

Seasonally distinct taxonomic and functional shifts in macroinvertebrate communities following dam removal

Dam removal is an increasingly popular restoration tool, but our understanding of ecological responses to dam removal over time is still in the early stages. We quantified seasonal benthic macroinvertebrate density, taxonomic composition, and functional traits for three years after lowhead dam removal in three reaches of the Olentangy River (Ohio, USA): two upstream of former dam (one restored, one unrestored), and one downstream of former dam. Macroinvertebrate community density, generic richness, and Shannon–Wiener diversity decreased between ∼9 and ∼15 months after dam removal; all three variables consistently increased thereafter. These threshold responses were dependent on reach location: density and richness increased ∼15 months after removal in upstream reaches versus ∼19 months downstream of the former dam. Initial macroinvertebrate density declines were likely related to seasonality or life-history characteristics, but density increased up to 2.27× from year to year in three out of four seasons (late autumn, early spring, summer) across all reaches. Macroinvertebrate community composition was similar among the three reaches, but differed seasonally based on non-metric multidimensional scaling (NMDS) and analysis of similarity (ANOSIM). Seasonal differences among communities tended to decrease after dam removal. We detected community-wide shifts in functional traits such as multivoltinism, depositional habitat use, burrowing, and collector-gatherer feeding mode. We observed that these traits were expressed most strongly with Chironomidae, which was the most abundant family. Our results suggest that seasonal environmental conditions can play a role in the response and recovery of macroinvertebrate communities—often used to monitor ecosystem condition—following dam removal. In particular, macroinvertebrate density and diversity can show recovery after dam removal, especially in seasons when macroinvertebrate density is typically lowest, with concomitant changes to functional trait abundance. Thus, we recommend scientists and managers consider responses to dam removal throughout the year. Further, similar density, generic richness, and functional traits among reaches suggest that channel restoration after dam removal may initially have equivocal effects on invertebrate communities.

Caddisflies (Trichoptera) in benthic communities of southern Sakhalin rivers, Far East Russia

During one year we studied caddisfly assemblages in benthic macroinvertebrate communities of mountain (Frikena River) and piedmont (Partizanka River) reaches of the Lyutoga River Basin. For most of the year in the mountain reaches, the scraper Neophylax ussuriensis Martynov dominates. Maximum caddisfly density (403 ind./m2) and biomass (14,441 g/m2) was recorded in July before mass emergence of that dominant species. The density of caddisflies in the benthic community was more significant in November (32%), and caddisfly biomass was most significant in July (69%). In the piedmont reaches of Lyutoga River Basin in various seasons, Rhyacophila (Hyporhyacophila) sp., Hydatophylax sp., Hydropsyche orientalis Martynov, and Stenopsyche marmorata Navás dominated. Maximum density and biomass of caddisflies (451 ind./m2, 1,576 g/m2) were recorded in 5 September. The density of filterers H. orientalis and S. marmorata occurs in the salmon spawning season and seems to be correlated with the increased abundance of suspended organic substances in the water column as salmon spawn. In the piedmont reaches the role of caddisflies are the most significant in September (49% of total macroinvertebrate density and 56% of biomass).

The effects of tricyclazole treatment on aquatic macroinvertebrates in the field and in laboratory

The effects of tricyclazole treatments on benthic macroinvertebrates in the field and in laboratory were studied. In field conditions, low density of benthic populations was observed, both in treated and untreated plots, which was attributed to the short period of submersion of the rice field and high water temperature, fungicide treatments had no significant effect. Both laboratory acute toxicity test and a test using a mesocosm suggested a low toxicity of tricyclazole on invertebrates. A reduction of the macroinvertebrate density was observed only when tricyclazole concentration was applied at concentrations 100 times the ones tested in the field, acute toxicity test gave an LC₅₀ after 48 h of 26 mg*L^–1, in agreement with data obtained for other species.

Effect of Typha domingensis cutting: response of benthic macroinvertebrates and macrophyte regeneration

Wetlands are important because they have high biodiversity and are considered, by environmental agencies, permanently protected areas due to their importance to conservation. In Southern Brazil the aquatic macrophyte Typha domingensis is harvested to be used in the manufacture of handicraft, being an important income source to small farmers. This work aims to test the cut effect of T. domingensis on benthic macroinvertebrates as well as on macrophyte regeneration. These phenomena were analyzed in small areas (1 m²) in a T. domingensis stand by comparing cut treatments and control treatments. Macroinvertebrate were sampled with a corer in the following time sequence after the cut event in both treatments: one day, 26 days, 60 days, 89 days, and 182 days. Macrophyte regeneration was monitored through monthly measurements at each treatment. The macroinvertebrate density did not differ between treatments (ANOVA, p < 0.05). Among the 23 taxa identified, Tubificidae was the only family to response to cut treatment. DCA showed an overlapping between treatments indicating a not clear pattern. The growth of T. domingensis shoots was not affected by the disturbance. Macrophyte regeneration was quick when comparing the treatments and statistical differences were found in one day after the disturbance and 26 days after the disturbance, whereas no differences were found in the remaining sampling dates (60, 89 and 182 days). Observing the macroinvertebrate response and the T. domingensis regeneration, our results suggest that sustainable use of this macrophyte is possible on a small scale.

Hudson River Fishes and their Environment

<em>Abstract.</em>—We compared nekton density and benthic prey availability over a range of flooding conditions within common reed <em>Phragmites australis </em>and narrowleaf cattail <em>Typha angustifolia </em>at a mesohaline and an oligohaline marsh on the Hudson River Estuary. Nekton were sampled using lift nets at high and low elevations. Marsh surface nekton sampling occurred on 16 high tide events from May–October 1999 and 2000. Hydrology (depth, duration, and frequency) was simultaneously measured. Benthic macroinvertebrate density and richness were measured from sediment cores in June, August, and October, coincident with lift net collections. A total of 690 individuals representing nine species, mostly mummichog <em>Fundulus heteroclitus </em>and daggerblade grass shrimp <em>Palaemonetes pugio </em>were captured within both vegetation types. Mean nekton density (individuals 6 m^-2 ± SE) on the marsh surface was not significantly different among reed at the mesohaline marsh (4.1 ± 1.3) and reed (3.4 ± 0.6) and cattail (4.1 ± 0.9) at the oligohaline marsh. Nekton density did not vary predictably across the measured range of flooding depth and duration. Nekton density was also not predictably related to benthic macroinvertebrate density or taxonomic richness. Significantly more juvenile mummichog were collected within cattail relative to reed, suggesting that spawning success of this species may be lower in reed. Adult resident fish and macrocrustacean species are distributed similarly within and between reed and cattail when they experience comparable flooding regimes. The present study represents one of the first direct measures of nekton density within reed and corroborates previous patterns for nekton abundance between reed and nonreed vegetation stands across a wide salinity regime.