Composition Of Macroinvertebrate Assemblages Research Articles

Climate warming shifts riverine macroinvertebrate communities to be more sensitive to chemical pollutants.

Freshwaters are highly threatened ecosystems that are vulnerable to chemical pollution and climate change. Freshwater taxa vary in their sensitivity to chemicals and changes in species composition can potentially affect the sensitivity of assemblages to chemical exposure. Here we explore the potential consequences of future climate change on the composition and sensitivity of freshwater macroinvertebrate assemblages to chemical stressors using the UK as a case study. Macroinvertebrate assemblages under end of century (2080-2100) and baseline (1980-2000) climate conditions were predicted for 608 UK sites for four climate scenarios corresponding to mean temperature changes of 1.28 to 3.78°C. Freshwater macroinvertebrate toxicity data were collated for 19 chemicals and the hierarchical species sensitivity distribution model was used to predict the sensitivity of untested taxa using relatedness within a Bayesian approach. All four future climate scenarios shifted assemblage compositions, increasing the prevalence of Mollusca, Crustacea and Oligochaeta species, and the insect taxa of Odonata, Chironomidae, and Baetidae species. Contrastingly, decreases were projected for Plecoptera, Ephemeroptera (except for Baetidae) and Coleoptera species. Shifts in taxonomic composition were associated with changes in the percentage of species at risk from chemical exposure. For the 3.78°C climate scenario, 76% of all assemblages became more sensitive to chemicals and for 18 of the 19 chemicals, the percentage of species at risk increased. Climate warming-induced increases in sensitivity were greatest for assemblages exposed to metals and were dependent on baseline assemblage composition, which varied spatially. Climate warming is predicted to result in changes in the use, environmental exposure and toxicity of chemicals. Here we show that, even in the absence of these climate-chemical interactions, shifts in species composition due to climate warming will increase chemical risk and that the impact of chemical pollution on freshwater macroinvertebrate biodiversity may double or quadruple by the end of the 21st century.

Kelp holdfasts in the Great African Seaforest provide habitat for diverse assemblages of macroinvertebrates

Kelp forests along the southwestern and west coasts of South Africa, dominated by the species Ecklonia maxima and Laminaria pallida, are locally termed ‘the Great African Seaforest’. They form 3-dimensional biogenic habitats that provide 4 distinct microhabitats—canopy, fronds, stipe and holdfast—with the latter typically supporting the highest abundance and diversity of associated macroinvertebrates. The macrofauna inhabiting kelp holdfasts in South Africa have rarely been studied, resulting in a near complete lack of baseline data. In this study, macrobenthic assemblages from 40 E. maxima holdfasts were examined over 2 marine ecoregions and 4 locations. Macroinvertebrates were identified and counted for univariate and multivariate analyses using family-level data. A total of 120 families from 9 phyla were identified and were generally dominated by Arthropoda (48 families), Annelida (24 families) and Mollusca (23 families). Marine ecoregion had no significant effect on composition of macroinvertebrate assemblages, whereas location had a significant effect. There was no significant relationship between holdfast volume and macroinvertebrate diversity or abundance, suggesting that other environmental and physicochemical factors are important in determining community structure. This study serves as a baseline for future research aimed at understudied holdfast macroinvertebrate communities in the Great African Seaforest.

Road crossings change functional diversity and trait composition of stream-dwelling macroinvertebrate assemblages

Functional diversity is regarded as a key concept in understanding the link between ecosystem function and biodiversity, and is therefore widely investigated in relation to human-induced impacts. However, information on how the intersection of roads and streams (hereafter road crossings, representing a widespread habitat transformation in relation to human development), influences the functional diversity of stream-dwelling macroinvertebrates is still missing. The general aim of our study was to provide a comprehensible picture on the impacts of road crossing structures on multiple facets of the functional diversity of stream-dwelling macroinvertebrates. In addition, we also investigated changes in trait structure. Our research showed that road crossing structures had negative impacts on functional richness and dispersion; i.e., functional diversification. However, we found no significant impact on functional divergence and evenness components. We found a decrease in functional redundancy at road crossing structures. This indicates a reduced ability of the community to recover from disturbances. Finally, we found that road crossings drive stream habitat and hydrological changes in parallel with modification of the trait composition of stream-dwelling macroinvertebrate assemblages. All these results suggest that road crossings cause notable changes in the functional diversity of stream-dwelling macroinvertebrate assemblages.

Negligible native and significant alien colonization of artificial shoreline by macroinvertebrates in a large shallow lake (Lake Balaton, Hungary)

The aim of our study was to compare the richness and composition of macroinvertebrate assemblages in natural reed and artificial rip-rap habitats in a shallow lake 50+ years after shoreline modifications. Lake Balaton (Hungary) provided a unique study system as approximately half of its shoreline (c.105 km) has been modified. Littoral macroinvertebrates were collected in two habitat types (artificial rip-rap and natural reed) around the shoreline over two seasons. We found that native taxon richness of rip-rap habitat was only one-twentieth of the natural reed habitat. Rip-rap habitat harboured significantly more alien species. We found that the proportion of alien taxa was higher in rip-rap habitat (89.2%) than in reed habitat (16.7%). The composition of macroinvertebrate assemblages in the two habitats was also significantly different with limited to moderate overlap. Furthermore, all 8 indicator taxa of rip-rap habitat were alien, whilst all 28 indicator taxa were native in reed habitat. These results suggest that artificial engineering structure creates a novel ecosystem dominated by alien species.

Influencia de las prácticas agrícolas en los ensambles de macroinvertebrados en la Patagonia (Argentina)

Aquatic species in agricultural areas are often exposed to concentrations of pesticides and fertilizers that can affect the entire community. This study aimed to monitor the presence of nutrients and pesticides (organophosphates and carbamates) and evaluate their effects on the composition of macroinvertebrate assemblages at two sites in the Neuquén River, both upstream (UNR) and downstream (DNR) of an area of intensive cultivation of pome fruit trees. Physicochemical parameters in water samples from UNR and DNR were not significantly different, except for nitrate (NO3-). Pesticides analyzed were below detection limits in water and sediment samples. Insects constituted 52.76% of the total individuals in UNR and, among them, Ephemeroptera was the most abundant taxon (n=419). On the other hand, 67.67% of the individuals in DNR were insects, and most of them belonged to the Order Diptera (n=1156). The abundance of Diptera and Ephemeroptera individuals was significantly different between sites. In addition, the temporal variation of richness within each site showed significant differences (P<0.05). There were 15 shared species and a Jaccard’s abundance-based index indicated 37.8% taxonomic similarity. In summary, there were no significant differences in abundance and diversity between UNR and DNR. However, there were differences in taxa richness and composition, with a low percentage of similarity between sites. The above can be observed in the canonical correspondence analysis, which shows a clear relationship between environmental variables and the distribution pattern of macroinvertebrate assemblages.

Natural stress vs. anthropogenic pressure. How do they affect benthic communities?

This study compares the role of salinity regime and chemical pollution in the biodiversity patterns of estuarine benthic communities. A specific field survey allowed us to explain the response of organisms to mixtures of chemicals and the effects of salinity regime and extreme events on the richness and composition of macroinvertebrate assemblages. The patterns obtained provide further evidence that both stress sources are key factors in macroinvertebrate communities' organization, but the type and magnitude of the changes differ. The abundance of opportunistic species increased according to the pollution gradient, while this indicator was less sensitive to salinity descriptors. In contrast, biotic indices responded to the salinity regime but did not show a consistent pattern in response to pollutants. Multivariate analyses reflected both environmental stress gradients. Overall, the results suggested that diversity increased in the habitats where the frequency and duration of extreme drought and flood events were low.

Beta-diversity of macroinvertebrates associated to Pocillopora corals along the Mexican Pacific coast

Although invertebrates are the most diverse organisms associated with corals, they have been poorly studied in the Eastern Tropical Pacific. Thus, this study analyzed macroinvertebrate assemblages associated with Pocillopora corals along the Mexican Pacific coast and assessed whether a latitudinal diversity gradient can be identified. Forty-two sites grouped in 12 localities were sampled by visual censuses from the southern Gulf of California (26° N) to the coast of Oaxaca (15° N). Ecological indices (species richness, abundance, and taxonomic distinctiveness) were compared among localities. A Bray–Curtis resemblance matrix was also created, and a non-metric multidimensional scaling (nMDS) was performed to identify locality groups based on macroinvertebrate abundance and occurrence. Beta-diversity as a measure of the proportional species turnover was determined in each locality group. A total of 129 species grouped in six phyla were recorded. All the ecological indices differed significantly among localities. Five groups that moderately followed a geographic pattern were formed by nMDS. Nevertheless, no evidence of a beta-diversity latitudinal gradient was found. Beta-diversity calculated in each group indicated that the central region of the Mexican Pacific and the Gulf of California have the highest species proportion in the studied area. Furthermore, the composition of macroinvertebrate assemblages had a “turnover and nestedness” beta-diversity pattern. These results are very useful for conserving species richness associated to coral communities along the Mexican Pacific coast. Establishment of marine protected areas in locality groups with a high macroinvertebrate beta-diversity should be considered, especially when harmful human activities can affect it negatively.

Influence of environmental variables on macroinvertebrate community structure in Lianhuan Lake.

The structural characteristics of the macroinvertebrate community can effectively reflect the health status of lake ecosystems and the quality of the lake ecological environment. It is therefore important to identify the limiting factors of macroinvertebrate community structure for the maintenance of lake ecosystem health. In this study, the community composition of macroinvertebrate assemblages and their relationships with environmental variables were investigated in 13 small lakes within Lianhuan Lake in northern China. A self‐organizing map and K‐means clustering analysis grouped the macroinvertebrate communities into five groups, and the indicator species reflected the environmental characteristics of each group. Principal component analysis indicated that the classification of the macroinvertebrate communities was affected by environmental variables. The Kruskal–Wallis test results showed that environmental variables (pH, total phosphorus, nitrate, water temperature, dissolved oxygen, conductivity, permanganate index, and ammonium) had a significant effect on the classification of the macroinvertebrate communities. Redundancy analysis showed that mollusks were significantly negatively correlated with pH and chlorophyll a, while annelids and aquatic insects were significantly positively correlated with chlorophyll a and dissolved oxygen. Spearman correlation analysis showed that the species richness and Shannon's diversity of macroinvertebrates were significantly negatively correlated with total phosphorus, while the biomass of macroinvertebrates was significantly negatively correlated with pH. High alkalinity and lake eutrophication have a serious impact on the macroinvertebrate community. Human disturbances, such as industrial and agricultural runoff, negatively impact the ecological environment and affect macroinvertebrate community structure. Thus, macroinvertebrate community structure should be improved by enhancing the ecological environment and controlling environmental pollution at a watershed scale.

Considering mesohabitat scale in ecological impact assessment of sediment flushing

Benthic macroinvertebrates respond to several factors characterizing the physical habitats, as water depth, current and streambed substrate. Thus, anthropogenic disturbances altering these factors may have different effects on benthos, also depending on mesohabitats. These disturbances include sediment flushing operations, commonly carried out to recover reservoir capacity, and investigating their effects at mesohabitat scale could be relevant for an adequate ecological impact assessment of these operations. Here, we compared benthic macroinvertebrate communities sampled before and after a controlled sediment flushing operation in three different mesohabitats (a pool, a riffle and a step-pool) of an Alpine stream. Contrary from expectations, the composition of macroinvertebrate assemblages was not significantly different among mesohabitats. Moreover, the impact of sediment flushing was more significant in terms of density rather than in richness. Two stressor-specific indices were tested, but only one (the Siltation Index for LoTic EcoSystems − SILTES) clearly detected the impact of sediment flushing on the macroinvertebrate community structure. Finally, some differences in the temporal trajectories and recovery times to pre-flushing conditions were observed among mesohabitats, both if the three mesohabitats were considered separately and if all their possible combinations were accounted for. Particularly, riffle was the most sensitive mesohabitat, not fully recovering one year after the sediment disturbance.

Evaluación de la calidad del agua a lo largo de una cuenca heterogénea (Río Grande, Jujuy, Argentina)

The aim of this work is to evaluate the ecological quality of waters along an environmentally heterogeneous basin, using macroinvertebrate biotic indices (BI). Twelve sampling sites were selected in the Río Grande basin, following an altitudinal gradient across the Puna, Monte and Yungas ecoregions. Sampling was conducted in the dry and rainy seasons, during three consecutive years (2012 to 2014). At each site, physico-chemical parameters were measured and benthic macroinvertebrates were collected. Principal component analysis (PCA) was applied to explore environmental variability in terms of physico-chemical parameters. The water quality of the basin was assessed by means of different biotic indices. Correlation analyses were performed between the biotic indices and the physicochemical parameters. Altitude, NaCl, total dissolved solids (TDS) and electrical conductivity were higher at the Puna and Monte sites, while river discharge, width and depth were higher at the Yungas sites. Biotic indices suggested good water quality. The BMWP (Biomonitoring Working Party) and family richness were the most suitable indices to simultaneously compare the rivers of the different ecoregions. The change in the composition of macroinvertebrate assemblages was observed at an altitude of 1500 m a. s. l., separating arid and humid zones and coinciding with inflection points of conductivity, NaCl and TDS.

Evaluación de la calidad del agua a lo largo de una cuenca heterogénea (Río Grande, Jujuy, Argentina)

The aim of this work is to evaluate the ecological quality of waters along an environmentally heterogeneous basin, using macroinvertebrate biotic indices (BI). Twelve sampling sites were selected in the Río Grande basin, following an altitudinal gradient across the Puna, Monte and Yungas ecoregions. Sampling was conducted in the dry and rainy seasons, during three consecutive years (2012 to 2014). At each site, physico-chemical parameters were measured and benthic macroinvertebrates were collected. Principal component analysis (PCA) was applied to explore environmental variability in terms of physico-chemical parameters. The water quality of the basin was assessed by means of different biotic indices. Correlation analyses were performed between the biotic indices and the physicochemical parameters. Altitude, NaCl, total dissolved solids (TDS) and electrical conductivity were higher at the Puna and Monte sites, while river discharge, width and depth were higher at the Yungas sites. Biotic indices suggested good water quality. The BMWP (Biomonitoring Working Party) and family richness were the most suitable indices to simultaneously compare the rivers of the different ecoregions. The change in the composition of macroinvertebrate assemblages was observed at an altitude of 1500 m a. s. l., separating arid and humid zones and coinciding with inflection points of conductivity, NaCl and TDS.

Homogenization of Macroinvertebrate Assemblages and Asiatic Clam Corbicula fluminea Invasion in a River of the Arid Patagonian Plateau, Argentina

The invasion of the Asiatic clamCorbicula flumineain South America has already reached Patagonia. Despite the well-known direct and indirect impacts that this species exerts on fresh-water ecosystems, particularly on benthic communities, few studies have been undertaken on its effect on the composition and structure of aquatic macroinvertebrate assemblages. This study evaluated the effects of the invasion of the Asiatic clamC. flumineaon the aquatic macroinvertebrate assemblages of the Limay River, one of the most important rivers of the arid plateau of Argentinian Patagonia. As this river is currently in the process of being invaded, it was possible to compare invaded and non-invaded sites. Invaded sites displayed a certain homogenization of their constituent species and functional composition. Non-metric multidimensional scaling, similarity analysis and similarity percentages showed negative or positive influence of the presence of this species on the abundance of some taxa, due to competition for resources in this low-productivity Patagonian ecosystem. The deposition of the faeces and pseudo-faeces ofC. flumineaenriches the organic content of the sediments. However, its pedal feeding can function as a competitive strategy: by consuming its own deposited organic matter when food is scarce, the amount available to other macroinvertebrates is reduced. This paper is the first contribution on the impact of this invasion on northern Patagonia’s aquatic macroinvertebrate assemblages.

Biotic indices of hydrological variability as tools to inform dynamic ecological status assessments in river ecosystems

River biomonitoring uses biotic indices that assess human-induced degradation, including pollution, by comparison with type-specific static biological reference conditions. However, index scores that indicate pollution may reflect biological responses to natural hydrological variability associated with low flows and drying, leading biomonitoring schemes to misclassify sites as degraded. To address this, dynamic, site-specific adjustments of static biological reference conditions have been proposed, but current biomonitoring tools cannot facilitate implementation of these adjustments. We analyzed 329 samples from mediterranean-climate rivers in Greece, to evaluate the use of six stressor-specific macroinvertebrate-based indices of hydrological variability (CEFI, DEHLI, ELF, LIFE, LIFENZ, MIS-index) as tools to facilitate dynamic adjustments of static biological reference conditions. We examined macroinvertebrate assemblage responses to physicochemical and land use drivers in relation to each sample's hydrological conditions, as assessed by the six indices. We evaluated index performance beyond the region of development by exploring correlations among indices, including correlations with the region-specific Greek ELF index, for which 100% of taxa were represented. We also examined the influence of inorganic nutrient pollution on index performance by comparing index scores from samples with and without nutrient pollution. Season, water temperature, agricultural land use and nutrient pollution were major drivers of macroinvertebrate assemblage composition. Indices were positively correlated but correlation strength varied considerably, driven primarily by taxonomic representation (the proportion of sampled taxa included in each index's calculation), and potentially also by differences in river types, taxonomic resolution and sampling strategies. All indices identified site-specific hydrological conditions both in the presence and absence of nutrient pollution. We recommend the development of region-specific biotic indices of hydrological variability, or regional adaptation of existing indices, to represent 100% of the regional taxa pool and thus to enable acceptable performance beyond their region of development. Such indices could inform dynamic adaptation of static biological reference conditions by assessing site-specific hydrological conditions based on a macroinvertebrate assemblage, without the collection of additional, abiotic field data. Application of our proposed approach could prevent misclassification of ecological status, thus avoiding time-demanding and costly mismanagement of rivers and streams.

Influence of river regulation and instream habitat on invertebrate assemblage’ structure and function

Dams modify geomorphology, water quantity, quality and timing of stream flows affecting ecosystem functioning and aquatic biota. In this study, we addressed the structural and functional macroinvertebrate community alterations in different instream mesohabitats of two Portuguese rivers impaired by dams. We sampled macroinvertebrates in riffles, runs and pools of river sites downstream of the dams (i.e. regulated; n = 24) and in sites without the influence of the dams (i.e. unregulated; n = 7), assessing a total of 64 mesohabitats, following late spring-early summer regular flows. We found a distinct taxonomic structure and trait composition of macroinvertebrate assemblages between regulated and unregulated flow sites, and also between mesohabitats in which the differences were more evident. When analysing each mesohabitat individually, the effect of flow regulation was detected only in run-type mesohabitats for both taxonomic and trait composition, leading us to infer that a selective macroinvertebrate assessment on run mesohabitats would be a valuable contribution to detect regulated flow effects on ecosystems impaired by dams. Additionally, there is evidence that respiration and locomotion traits could be effective tools to identify damming flow alterations. This study supports that the quality assessments of rivers impacted by dams could benefit from a sampling approach focused on run mesohabitats and the detection of some key traits, which would improve assessment accuracy.

Long-term monitoring reveals convergent patterns of recovery from mining contamination across 4 western US watersheds

Long-term studies of stream ecosystems are essential for assessing restoration success because they allow researchers to quantify recovery trajectories, gauge the relative influence of episodic events, and determine the time required to achieve clean-up objectives. To quantify responses of benthic macroinvertebrate assemblages to stream remediation, we integrated results of 4 long-term (20–29 y) assessments of mining-impacted watersheds that were broadly distributed across the western US (California, Colorado, Idaho, Montana). Using a before–after control–impact (BACI) study design, we observed substantial reductions in metal concentrations and corresponding improvements of benthic assemblages following remediation. Recovery rates were relatively consistent, and streams typically recovered within 10 to 15 y after remediation was initiated (mean = 10.25 y), although episodic events changed trajectories at some sites. Differences in recovery among watersheds were likely determined by a number of factors, including the severity of contamination, effectiveness of remediation, proximity to upstream sources of colonization, and hydrologic variation. We also observed considerable variation in the rate and extent of recovery among assemblage metrics. For example, total abundance and richness recovered rapidly at most sites, but the composition of benthic macroinvertebrate assemblages remained substantially altered compared with reference sites. Using piecewise linear regression, we estimated a threshold response of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species richness at ~1 cumulative criteria unit (CCU), which is the sum of the fractions of chronic water-quality criteria for metals measured, suggesting this value was protective of benthic assemblages. However, EPT richness was reduced by ~20% at 2× this CCU value, indicating that moderate exceedances of water-quality criteria could substantially affect stream biodiversity. Non-metric multidimensional scaling analyses identified common sets of species trait states across the 4 watersheds that were associated with either metal contamination or with recovering and intact reference stream assemblages. Our study illustrates the importance of long-term studies for quantifying responses to stream restoration and the usefulness of BACI designs for demonstrating cause-and-effect relationships between restoration treatments and community recovery. Because these 4 watersheds were among the most severely polluted sites in the western US, our study demonstrates the value of these investments in watershed restoration and the potential for success under the most extreme conditions.

Attenuation of insecticide impact by a small wetland in a stream draining a horticultural basin in Argentina

Horticulture has greatly increased in Argentina in recent decades mainly due to increasing greenhouse utilization and agrochemical consumption, thus representing a threat to adjacent water bodies. Riparian wetlands, however, could attenuate agrochemical contamination. The present work therefore compared insecticide concentrations in bottom sediments in addition to sediment toxicity to the amphipod Hyalella curvispina and investigated the macroinvertebrate composition upstream and downstream from a natural wetland in a small stream draining a basin undergoing intense horticultural production. The wetland surface was covered by macrophytes, mainly Thypha sp., and the insecticide concentrations measured downstream from the wetland were significantly lower, at roughly 19% of the upstream values. The growth rates of H. curvispina were significantly higher when exposed to the sediments downstream from the wetland, while the macroinvertebrate-assemblage composition was significantly different upstream and downstream: the snail Pomacea canaliculata was the dominant species upstream while the amphipod H. curvispina was dominant downstream. Pomacea canaliculata is often the dominant species in the regional streams draining agriculture and horticultural basins. Hyalella curvispina is sensitive to pesticide toxicity and is often dominant in streams draining extensive livestock basins and within a biosphere reserve. We conclude that riparian wetlands effectively attenuate horticulture contamination in pampean streams and should therefore be preserved and restored.

Do wider riparian zones alter benthic macroinvertebrate assemblages’ diversity and taxonomic composition in neotropical headwater streams?

Abstract: Aim The maintenance and condition of riparian vegetation are important factors for conserving headwater streams and their species diversity. Thus, variations in the width of a riparian zone can have dramatic effects in the structure and functioning of the adjacent freshwater ecosystem. In this study, we aimed to determine if increased riparian zone width changed the benthic assemblages’ structure (diversity, taxonomic and functional composition) in headwater streams. Methods We tested two predictions: (1) increased riparian zone width will change the diversity and taxonomic composition of benthic macroinvertebrate assemblages because narrow riparian zones do not buffer the anthropogenic impacts from the surrounding landscape; (2) wider riparian zones will change benthic macroinvertebrate assemblages’ functional structure, due to changes to energetic input and quality. To test the first prediction, we assessed the benthic macroinvertebrate assemblages’ taxonomic composition, richness and Shannon-Wiener diversity index. To test the second prediction, we assessed functional feeding groups (FFG) and metrics based on their proportion. Results Our results showed that our first prediction was not corroborated, because taxonomic structure and diversity did not show significant variation with increased riparian zone width. Our second prediction was partially corroborated, because there were significant alterations in the functional structure of benthic macroinvertebrate assemblages between the narrowest riparian zone width (30 m) and the others two (50 and 100 m). Conclusions Our results suggest that, contrary to the Brazilian Federal Law 12651/2012, 30-m wide riparian zones are insufficient to protect headwater stream ecosystem functioning.

Macroinvertebrates of Eichhornia crassipes (Pontederiaceae) roots in the alluvial floodplain of large tropical rivers (Argentina)

Introduction: Eichhornia crassipes is a dominant aquatic plant of neotropical-river floodplains and is invasive in warm waters of different continents. Plants provide food and habitat for fish, especially Prochilodus lineatus and Gymnotus omarorum, which are relevant to subsistence fishing by local indigenous communities. Objective: In this study we describe the main traits of E. crassipes floating meadows, and analyze the abundance and composition of macroinvertebrate assemblages associated with their roots in two floodplain wetlands of the Paraná River (within the Ramsar site Wetlands Chaco) and of the Pilcomayo River (within the Pilcomayo River National Park). Methods: During spring and summer, the macroinvertebrates were collected in monospecific stands of E. crassipes with a net of 962 cm2 area and 500 µm mesh size. Leaf density, the biomass of leaves and roots, the length of leaves and roots, and the water quality were measured simultaneously. Results: Temperature, oxygen concentration, and nutrient content were significantly higher and electrical conductivity was lower in the Pilcomayo than in the Paraná floodplain. E. crassipes growing in the Pilcomayo floodplain had longer leaves and less root biomass than those found in the Paraná floodplain. The number of macroinvertebrates per 1 000 g root dry weight and per m2 was significantly different between both floodplains, but the taxon richness was similar. Non Metric Multidimensional Scaling analysis differentiated the abundance of 14 selected taxa between both floodplains, and showed a high correlation between the environmental variables and macroinvertebrate abundance. The most abundant taxonomic groups in the Paraná River floodplain were oligochaetes (Naididae), ostracods mainly Cytheridella ilosvayi and larvae of non-biting midges (Chironomidae). Two families, Hydrobiidae (Heleobia parchappii) and Chironomidae accounted for 49.3 % of the total abundance in the Pilcomayo floodplain. The prawns Macrobrachium jelskii and M. amazonicum, frequent in the Pilcomayo floodplain, were not found in the Paraná floodplain. Conclusions: The different environmental conditions in both floodplains affect the abundance, composition, and the dominance of macroinvertebrate assemblages; however, the total taxa richness was similar. The area occupied by E. crassipes in the floodplains of these rivers provides the habitat that contributes most to overall biotic diversity, which must be considered in management strategies.

Climate- versus geographic-dependent patterns in the spatial distribution of macroinvertebrate assemblages in New World depressional wetlands.

Analyses of biota at lower latitudes may presage impacts of climate change on biota at higher latitudes. Macroinvertebrate assemblages in depressional wetlands may be especially sensitive to climate change because weather-related precipitation and evapotranspiration are dominant ecological controls on habitats, and organisms of depressional wetlands are temperature-sensitive ectotherms. We aimed to better understand how wetland macroinvertebrate assemblages were structured according to geography and climate. To do so, we contrasted aquatic-macroinvertebrate assemblage structure (family level) between subtropical and temperate depressional wetlands of North and South America using presence-absence data from 264 of these habitats across the continents and more-detailed relative-abundance data from 56 depressional wetlands from four case-study locations (North Dakota and Georgia in North America; southern Brazil and Argentinian Patagonia in South America). Both data sets roughly partitioned wetland numbers equally between the two climatic zones and between the continents. We used ordination methods (PCA and NMDS) and tests of multivariate dispersion (PERMDISP) to assess the distribution and the homogeneity in variation in the composition of macroinvertebrate assemblages across climates and continents, respectively. We found that macroinvertebrate assemblage structures in the subtropical depressional wetlands of North and South America were similar to each other (at the family level), while assemblages in the North and South American temperate wetlands were unique from the subtropics, and from each other. Tests of homogeneity of multivariate dispersion indicated that family-level assemblage structures were more homogeneous in wetlands from the subtropical than the temperate zones. Our study suggests that ongoing climate change may result in the homogenization of macroinvertebrate assemblage structures in temperate zones of North and South America, with those assemblages becoming enveloped by assemblages from the subtropics. Biotic homogenization, more typically associated with other kinds of anthropogenic factors, may also be affected by climate change.

Assessment of the Effects of Sediment-Associated Metals and Metalloids on Mangrove Macroinvertebrate Assemblages

Although much previous research effort has examined the impacts of metal contamination on macrobenthic assemblages in subtidal sediments, little attention has been directed at macroinvertebrate responses in intertidal mangrove habitats. Thus, in order to assess the unique responses of mangrove macroinvertebrate assemblages to sediment metal(loid) contamination, total, normalised and bioavailable metal(loid)s (Mn, Pb, Cr, Cd, As, Se, Co, Ni, Zn and Cu) were assessed within and between four mangrove locations in Lake Macquarie, NSW, Australia, and compared to resident macroinvertebrate assemblages over two sampling occasions. Mangrove biomass and physicochemical properties of sediment are known to influence macroinvertebrate assemblages, and as such, were also assessed to account for any potential confounding effect on macroinvertebrate assemblage composition. Significant differences in total and bioavailable metal(loid) contamination were found between and within locations and were consistent over time. Sediments at contaminated locations presented a high risk to biota with bioavailable concentrations of Pb, Cd, Zn found to exceed sediment quality guidelines and concentrations of Se capable of adverse impacts to biota. Macroinvertebrate assemblage composition varied with metal(loid) contamination loads present at study locations. Metal(loid) contamination was significantly correlated with macroinvertebrate assemblages over two sampling periods. Further analysis revealed that 71% of macroinvertebrate assemblage composition could best be explained by a combination of five variables namely, bioavailable Mn, Zn, and Se, number of mangrove seedlings and mean mangrove biomass. Rather than tolerant polychaetes dominating metal(loid)-contaminated sediments (as is found generally in subtidal sediments), polychaetes in intertidal mangroves appeared to be relatively sensitive to metal(loid) stress. Further, decapod crustaceans in the family, Varunidae, and gastropod molluscs, in the family, Amphibolidae, were found to be metal-sensitive taxa and may be employed in future studies as indicator taxa of sediment metal(loid)-related impacts in south-eastern Australian mangrove forests.