Macroinvertebrate Samples Research Articles

Influence of granulometry on the distribution of benthic macro invertebrates in some streams of the Mvilla and Haut-Nyong watersheds in Cameroon

This study was conducted from November 2018 to October 2019 in 8 forested streams in the Haut-Nyong and Mvilla watersheds to determine the influence of substrates granulometry on benthic macroinvertebrates. The physicochemical analyses showed highly oxygenated, weakly mineralized and slightly acidic waters. The granulometric analyses reveal 9 categories of substrates depending on the scale of sand, sand+gravel or sand+mud. Sampling of benthic macroinvertebrates allowed the collection of 15058 organisms divided into 5 classes, 14 orders and 49 families. The results showed a taxonomic richness strongly influenced by the nature of the substrate. The combination of coarse sand + silt + dead leaves was more favored the development of benthic macroinvertebrates with 48 families. The taxonomic richness associated to the different index revealed good ecological quality of Sounou, Bengo'o and Lo'o rivers.

Longitudinal Changes in Diverse Assemblages of Water Mites (Hydrachnidia) along a Lowland River in Croatia

Water mites are the most diverse freshwater group of Acari and despite growing research interest in the ecology of this group, the environmental influences along longitudinal river gradients on their assemblages are still not fully understood. The objective of this study was to determine how physico-chemical water properties and hydromorphological alterations affect the composition and distribution of water mite assemblages along a longitudinal river gradient. Macroinvertebrate samples were collected from 20 study sites distributed longitudinally along the entire 106 km course of a lowland river (Bednja River) in the Pannonian Lowlands ecoregion of Croatia. At each site, 20 samples were collected with regard to microhabitat composition (+400 samples in total). In parallel with the sampling of macroinvertebrates at each site, the physico-chemical water properties were measured and the degree of hydromorphological alteration was assessed (European Standard EN 15843:2010). Both the number of taxa and water mite abundance were found to increase significantly with increasing distance from the source. However, the assemblages from the upper reaches and those from the lower reaches shared very few species, emphasizing the importance of species-level identification. Water mite species richness and diversity were not reduced with increased levels of variables associated with organic enrichment and eutrophication pressures. Similarly, hydromorphological alteration did not reduce either water mite abundance or species richness and was positively correlated with both. Furthermore, a correspondence analysis on water mite microhabitat preferences revealed that 32% of all species were positively associated with artificial microhabitats (technolithal). These positive associations may be the result of reduced competitive pressure from other larger invertebrates, as well as a possible preference for higher velocity, which usually occurs on smooth technolithal surfaces. A total of 22 different species of water mites were found during this study, 8 of which (or 36% of all species found) were recorded for the first time in Croatia.

Automatic Image Processing to Determine the Community Size Structure of Riverine Macroinvertebrates.

Body size is an important functional trait that can be used as a bioindicator to assess the impacts of perturbations in natural communities. Community size structure responds to biotic and abiotic gradients, including anthropogenic perturbations across taxa and ecosystems. However, the manual measurement of small-bodied organisms such as benthic macroinvertebrates (e.g., >500 µm to a few centimeters long) is time-consuming. To expedite the estimation of community size structure, here, we developed a protocol to semi-automatically measure the individual body size of preserved river macroinvertebrates, which are one of the most commonly used bioindicators for assessing the ecological status of freshwater ecosystems. This protocol is adapted from an existing methodology developed to scan marine mesozooplankton with a scanning system designed for water samples. The protocol consists of three main steps: (1) scanning subsamples (fine and coarse sample size fractions) of river macroinvertebrates and processing the digitized images to individualize each detected object in each image; (2) creating, evaluating, and validating a learning set through artificial intelligence to semi-automatically separate the individual images of macroinvertebrates from detritus and artifacts in the scanned samples; and (3) depicting the size structure of the macroinvertebrate communities. In addition to the protocol, this work includes the calibration results and enumerates several challenges and recommendations to adapt the procedure to macroinvertebrate samples and to consider for further improvements. Overall, the results support the use of the presented scanning system for the automatic body size measurement of river macroinvertebrates and suggest that the depiction of their size spectrum is a valuable tool for the rapid bioassessment of freshwater ecosystems.

Channel abandonment alters trophic characteristics of highland rivers

The Qinghai-Tibet Plateau (QTP) serves as a collection of unique ecosystems featured as oligotrophic and hypometabolic conditions, and is particularly vulnerable to threats posed by anthropogenic and natural disturbances. Active fluvial processes on the QTP, especially the lateral migration of rivers and channel abandonment accompanied by variations in the hydrological connectivity, and changes in river geomorphology, intensively modify this highland river-floodplain system. However, little is known about how these processes alter the trophic characteristics of highland river system on earth. In this study, we conducted field investigations on a typical meandering river, the Quanji River (QR), located in the northeastern QTP by sampling macroinvertebrates, surveying trophic sources, and measuring a range of environmental conditions. Based on the collected data, we identified four biotopes for the QR through hierarchical clustering, established the representative food web for each biotope through the allometric diet breadth model, and estimated the biomass storage and flux within food web for each biotope through the biomass balance model. Our results show that the identified biotopes differed markedly in hydrological connectivity. Biotopes 1 and 2, which were in the main river channel represented the condition of high connectivity, Biotope 3 in the open channel represented the median connectivity, while Biotope 4 in the semi-open/closed channel represented the low connectivity. In contrast to the unimodal pattern commonly observed in lowland rivers, indices for the highland QR, including the taxa richness, trophic group richness, biomass flux, biomass transfer efficiency, and trophic stability demonstrated a single-valley response pattern to the hydrological connectivity. We argue that the intermediate disturbance hypothesis still works on highland river ecosystems, whereas the optimal disturbance occurs in the low connectivity rather than median connectivity. We attribute this skewness to the low resistance and resilience of highland macroinvertebrate community in the face of hydrodynamic disturbances brought by flood events, and the biological disturbances from the predation by endemic migratory fish (Gymnocypris przewalskii) in QR. This study reveals that lateral migration and channel abandonment play important roles in highland river systems in the QTP in the context of biological and energetic perspectives and suggests that management strategies for highland rivers should be made different from those of lowland rivers.

Long-term Macrobentos Responses to Environmental Flows and Water Quality improvement along River Jarama

The Jarama River, due to its proximity to Madrid, has been a highly regulated and polluted for decades; we evaluated the effects of changing multi-pressures over time and along the fluvial continuum. Changes in macrobenthic composition and structure in response to alterations in river habitat have been analyzed from two macroinvertebrate sampling campaigns carried out 42 years apart at 11 locations along the Jarama River. Results show that the macrobenthic communities follow a similar pattern along the river continuum in both periods. Richness and diversity were higher at mountain reaches without pollution and unregulated. The minimum values are reached at San Fernando de Henares, although in the lower part of the river, after receiving all the pollution discharges from the Manzanares River, there are no macrobenthos since the Jarama bottoms are anoxic sludge.Comparing the communities at the same localities we have detected clear temporal changes. In the upper zone, the total number of taxa and diversity decreased, but the fauna richness is maintained. In the section just below large reservoirs we find an increase in macrobenthos richness. In all the medium sections there is a recovery in all the macrobenthos parameters, but this improvement does not reach good ecological status, due to the high concentrations of ammonia. In the lower section, no changes are detected because the accumulated sludge is still present.

Investigation of the biological diversity of Trichoptera larvae in the streams of the Kastamonu (Cide)-Sinop (Ayancık) coastal region of Türkiye

This study was carried out to determine the biodiversity and densities of Trichoptera larvae at stations in the Kastamonu (Cide)-Sinop (Ayanc?k) coastal region. Benthic macroinvertebrate samples were collected from each of the 19 stations using the kick-net sampling method with a D-frame net (500-?m mesh). Using the data from collected Trichoptera larvae, the similarity, diversity, dominance and population density relationships among habitats were measured. According to the calculated Shannon-Wiener and Simpson diversity index results, the station with the highest Trichoptera diversity was determined at S2, and the station with the least diversity was S14. Similar results were obtained for the calculated population density values. Station S2 was the most balanced station in population density. Thus, biodiversity was directly related to habitat structure, anthropogenic impact and geographical conditions, and environmental factors suppress biological species diversity. It was concluded that species diversity is greater in undestroyed habitats and less in heavily destroyed habitats. In addition, the species that dominate in biodiversity similarity rates prefer their habitat.

New York State’s WAVE Method - Evaluation of a Method for Water Quality Monitoring by Citizen Scientists using Benthic Macroinvertebrates

New York State Department of Environmental Conservation (NYSDEC) has developed a robust citizen science macroinvertebrate sampling method. The metric relies on the presence and not the absence of key macroinvertebrates and therefore is resistant to collection and sorting errors. It identifies unimpaired streams with high confidence (0.1% type 1 errors) and at a reasonable efficiency compared to NYSDEC’s multimetric index of biological integrity (54%). We rank remaining stream samples for further investigation using a calculated probability of impairment. This method is valuable as a tool for large monitoring programs with limited resources for quality assurance checks. The value of this method goes beyond data collection, however, as data of known quality is an effective communication tool between citizen scientists and state regulatory agencies and/or local decision makers.

Assessment of benthic macroinvertebrate fauna as bio-indicator and physicochemical characteristics in the Gulf of Guinea off western Nigerian shor

Benthic macroinvertebrates are helpful bio-indicators providing better understanding of modified and perturbed aquatic ecosystems. This study seeks to determine the ecological status and diversity of the macroinvertebrate community in relation to environmental variables in western Nigerian offshore waters within the Gulf of Guinea. Macroinvertebrate samples were collected from five (5) sampling stations using a Van-veen grab following standard protocols. Water samples were collected and the physico-chemical parameters measured onboard using a multi-parameter checker, HORIBA-U53. The physico-chemical parameters of the water varied significantly (p<0.05) between stations. Macoma litoralis (13.71%), Tellina gilchristi (13.71%), and Tellina trilateri (11.71%) were the dominant macroinvertebrate species, while Nassarius cuvierii, Oxystele tigrina Tritia lanceolata Turritella communis, Turritella communis and Orbinia angrapequensis (0.33% each) were the least abundant. Axis 1 (63.73%) and axis 2 (22.32%) of the Canonical Correspondence Analysis (CCA) explained macrobenthic fauna-environmental variables association. Gastropoda showed strong relationship with salinity, silicate, sulphate, TDS and conductivity in Stations 1, 2 and 3. Bivalvia and Scaphopoda showed strong relationship with pH, BOD, water temperature, phosphate and nitrate in Stations 4 and 5. The AZTI Marine Biotic Index (AMBI, 0.85), multivariate AZTI Marine Biotic Index (M-AMBI, 0.80), Bentix Index (5.46) and Biotic Index (BI, 1.00) showed that this section of the Gulf of Guinea is undisturbed.

Specimen records of benthic macroinvertebrate samples collected by Norman H. Anderson in the vicinity of Mount St. Helens, 1980-1990

A private collection of 903 vials containing mostly aquatic macroinvertebrates is presented from Dr. Norman Herbert Anderson, Professor of Entomology at Oregon State University from 1962-1995. The majority of these specimens were collected from multiple freshwater streams during his research at Mount St. Helens (WA, USA) soon after the May 18, 1980 eruption. This collection also includes 15 vials containing specimens collected by Luis A. Fusté from the Muddy River (WA, USA) on March 29, 1980, less than 2 months before the eruption. The vast majority of these vials include a label indicating the sampling location, the date collected, and taxonomic identification.

New Deep-Sea Molluscan Records from Mallorca Channel Seamounts (North-Western Mediterranean)

Seamounts are globally important and essential ecosystems for supporting and maintaining marine biodiversity. In the Mallorca Channel, three prominent seamounts are present: Ausias March, Ses Olives and Emile Baudot. Currently, this area is being evaluated for inclusion in the Natura 2000 network. For this objective three surveys were conducted in the seamounts of the Mallorca Channel during July 2018 and July 2020. Samples of macro-invertebrates obtained in the deep sea revealed a rich fauna of Mollusca (68 species belonging to 40 families). New Mollusca occurrences included: four species of Gastropoda: Colus jeffreysianus, Cantrainea peloritana, Fusiturris similis, Gymnobela abyssorum, and seven species of Bivalvia: Pododesmus squama, Allogramma formosa, Asperarca nodulosa, Cetomya neaeroides, Spondylus gussonii, Haliris granulata and Policordia gemma. Where possible, the identification of these species was confirmed using the DNA barcoding method (sequencing of the cytochrome c oxidase subunit I). This study contributes towards filling the gap in knowledge of deep-sea mollusc fauna of the north-western Mediterranean.

Spatial Factors Outperform Local Environmental and Geo-Climatic Variables in Structuring Multiple Facets of Stream Macroinvertebrates' β-Diversity.

Simple SummaryOne of the key targets of community ecology and biogeography concerns revealing the variability and underlying drivers of biodiversity. Most current studies understand biodiversity based on taxonomic information alone. Our study was based on macroinvertebrates from 179 stream sampling sites in the Hun-Tai River Basin in Northeastern China. The correlation of different facets of β-diversity was compared while revealing the relative contribution of multiple abiotic factors (i.e., local environmental, geo-climatic, and spatial factors) to shaping β-diversity based on taxonomic, functional, and phylogenetic information. The results showed that functional β-diversity provides important complementary information to taxonomic and phylogenetic β-diversity. Moreover, spatial factors outperform local environmental and geo-climatic variables in structuring multiple facets of stream macroinvertebrates’ β-diversity. Our study provides guidance for future conservation studies of watershed biodiversity, as well as implications for future studies of β-diversity.One of the key targets of community ecology and biogeography concerns revealing the variability and underlying drivers of biodiversity. Most current studies understand biodiversity based on taxonomic information alone, but few studies have shown the relative contributions of multiple abiotic factors in shaping biodiversity based on taxonomic, functional, and phylogenetic information. We collected 179 samples of macroinvertebrates in the Hun-Tai River Basin. We validated the complementarity between the three facets and components of β-diversity using the Mantel test. Distance-based redundancy analysis and variance partitioning were applied to explore the comparative importance of local environmental, geo-climatic, and spatial factors on each facet and component of β-diversity. Our study found that taxonomic and phylogenetic total β-diversity was mainly forced by turnover, while functional total β-diversity was largely contributed by nestedness. There is a strong correlation between taxonomic and phylogenetic β-diversity. However, the correlations of functional with both taxonomic and phylogenetic β-diversity were relatively weak. The findings of variation partitioning suggested that distinct facets and components of macroinvertebrates’ β-diversity were impacted by abiotic factors to varying degrees. The contribution of spatial factors was greater than that of the local environment and geo-climatic factors for taxonomic, functional, and phylogenetic β-diversity. Thus, studying different facets and components of β-diversity allows a clearer comprehension of the influence of abiotic factors on diversity patterns. Therefore, future research should investigate patterns and mechanisms of β-diversity from taxonomic, functional, and phylogenetic perspectives.

Preliminary Research on Gastropoda Fauna in Some Fresh Waters of The Black Sea Region, Turkey

Commonly found in terrestrial and aquatic ecosystems, Gastropoda members are the class with the highest number of species within the Mollusca. Freshwater Gastropods which are generally listed in primary consumer play a crucial part in aquatic environments by feeding numerous fish species and vertebrate species. They include species that are widely distributed in rivers and lakes and are used as indicators in aquatic systems monitoring studies. In Turkey, the Black Sea Region is also a privileged geography in terms of its topography and historical development history of aquatic systems, rich in rivers and lakes. In this research, field studies were conducted from 20 different stations in the Black Sea region in 2017-2018. Benthic macroinvertebrate samples were collected from lakes and rivers with an Ekman grab sampler and hand net. Samples were washed in situ and fixed with 70% ethyl alcohol. Totally 10442 benthic macroinvertebrate members belong to 21 taxa were determined in the study. In the region, Oligochaeta was the dominant taxa with 56.80% dominancy value and followed by Chironomidae and Gastropoda with 18.26 and 8.24, respectively. As third dominant taxa, Gastropoda members were consist of 870 individuals belong to 11 taxa. It was determined that Gyraulus elenae and Radix labiata from Gastropoda were widely distributed in the region. These species have broad tolerance to pollution. In the study, it was determined that both densities of species and population were increased in the regions of the rivers that are far from the settlement areas or that have not been intervened and in the littoral parts of the lakes. In general, a decrease was observed not only in the Gastropoda members but also in the expected population density of the macrozoobenthos members in the parts of the streams that are under pressure.

A Comparison of the Efficiency of Aquatic Macroinvertebrate Sampling Tools Used in Lotic Environmental Impact Assessment of Human Activities in A Tropical Mountain Stream in Eastern Uganda

The study was aimed at comparing the efficiency of three macroinvertebrate sampling tools used in lotic environmental impact assessment of River Sipi including Surber sampler, rock-filled basket and Kick net sampling tools. The efficiency of the sampling tools was based on the data collected by each sampling tool, which was in turn used to calculate the Relative variation (RV) (efficiency), diversity, richness, and relative abundance, time taken to sort macroinvertebrate per sample and taxa assemblage. Data was analysed using a two-way ANOVA that was performed under the R Development Core Team 2010. The results indicated that despite the fact that all the sampling tools were efficient in sampling macroinvertebrates with RV<25%, both kick net and rock-filled basket obtained closely comparable efficiency results with Relative Variation ranging between 0.54-2% for the kick net and 1.4-3.6% for rock filled basket. Of the three sampling tools, the kick net was the most efficient, collecting a greater diversity of macroinvertebrate taxa (1.81±0.04) and a greater number of specimens (1444), abundance (66.4±0.25%), greater taxa richness (11±0.41) but required the biggest amount of time to sort macroinvertebrates (26±0.71minutes). In conclusion, the rock-filled basket served as the next best alternative efficient sampling tool to kick net in sampling macroinvertebrates.

Anthropogenic induced physicochemical gradients and associated macroinvertebrate community changes in derived savannah stream in Nigeria: Implication for biotic assessment

Understanding the impact of anthropogenic activities on various ecosystem matrices is fundamental to the application of biotic assessment. Here we explored the spatial changes of macroinvertebrate community structure under varying physicochemical gradients in Adoka Stream at Eziani Town, Southeast Nigeria. The water and macroinvertebrate samples were obtained from three stations positioned along the stretch of the stream with station 1 taken as a reference to others. We adopted Principal Component Analysis (PCA) and Canonical Correspondence Analysis (CCA) to analyse the monitored dataset comprising of 16 parameters with the aim to identify the important physicochemical parameters, and further evaluated the relationship between physicochemical parameters and macroinvertebrates assemblages. The PCA in first two rotated components (RCs) showed that turbidity, EC, NO₃, PO₄, SO₄, Cl, BOD₅, COD, DO, pH, and HCO₃ explained 57% of variance in the water quality dataset and associated macroinvertebrates assemblage. Based on the CCA, temperature, pH, turbidity, EC, NO₃, SO₄, DO, HCO₃, Ca, and Mg were important to predicting changes of macroinvertebrates assemblage structure in the stream. The observed variations of the water quality were reflected on macroinvertebrate assemblage across the stations. High abundance, taxa richness and pollution sensitive taxa of Trichoptera were obtained for station 1 with good water quality while stations 2 and 3 with significant influence from anthropogenic activities which resulted to degrading water quality had low abundance and taxa richness as well as dominance of pollution-tolerant taxa of Diptera groups. Dolophilodes urceolus and Leptonema natalense were the dominant taxa of the trichopterans while individuals of taxa Chironomus transvaalensis, Paraphaenocladius sp., and Pentaneura nilotica dominated the dipterans. In conclusion, our results provided useful information that supports the protocol for biotic assessment and also baseline data on physicochemical conditions and macroinvertebrate composition of the stream.

Land use effects on water quality, habitat, and macroinvertebrate and diatom communities in African highland streams

Anthropogenic activities have increasingly subjected freshwater ecosystems globally to various pressures. Increasing land use activities have been highly linked to deteriorating freshwater ecosystems and dwindling biodiversity. For sound management and conservation policies to be implemented, relations between land use, environmental, and biotic components need to be widely documented. To evaluate the impacts of land use on biotic components, this study analyzed the diatom and macroinvertebrate community composition of the Eastern Highlands (Zimbabwe) streams to assess the main spatial diatom and macroinvertebrate community variances and how environmental variables and spatial factors influence community composition. Diatom and macroinvertebrate sampling was done in 16 streams in protected areas (national parks) and impacted sites (timber plantation and communal areas). Water (pH, phosphorus, and ammonium) and sediment (nitrogen, phosphorus, calcium, magnesium, manganese, and zinc) and habitat (substrate embeddedness, and habitat) variables differed significantly with land use. Principal Component Analysis (PCA) showed that the protected area had the best water quality, particularly marked by high pH levels and low phosphorus concentrations among environment types. Heavy metals were high in the communal areas, although mercury was higher in the national park. Significant differences were observed in diatom metrics, specifically dominance and evenness, with no significant differences observed in macroinvertebrate metrics across land uses. Diatoms differed in terms of composition in response to land use. Results provide an important scientific reference for land use optimization and guidance for the formulation of policies to protect freshwater resources in African Highland streams. Management and conservation initiatives in the Eastern Highlands are further recommended as this study detected high levels of mercury in the protected area, implying high levels of illegal mining.

KUALITAS SUNGAI SELAGAN BENGKULU BERDASARKAN FISIKA-KIMIA PERAIRAN DAN KERAGAMAN MAKROINVERTEBRATA

This research aims to determine the quality of Selagan River, Bengkulu based on its water physico-chemical parameters and macroinvertebrate diversity. Data were collected at three stations, Lubuk Bangko (upstream), Lubuk Sahung (middle) and Tanah Rekah (downstream) in April 2019 represents the peak of rainy season, and September 2019 represents the peak of dry season. Macroinvertebrate sampling was carried out on three minutes sampling method, and the obtained samples were identified at least to the family level. The result indicated the physico-chemical of Selagan River are generally in a normal range, except for a bit higher temperature at Lubuk Sahung and Tanah Rekah during April sampling (31 and 32oC respectively). This research also found 508 of individual macroinvertebrates that were divided into 19 species (19 families; 4 class and 4 phyla). The Shannon wienner diversity index (H’) of macroinvertebrates from the upstream to downstream are 1.54; 2.20 and 0.84, while the Berger-Parker’s dominance index (BP) are ranging from 0.30 into 0.92. The number of EPT individual in each station from up- to downstream is 129; 40; and 0, with FBI index is 4.11; 5.23; and “infinity” consecutively. The combination of those several indices indicated that the upstream of Selagan river is still in a very good condition, the middle area is starting to degraded, while the downstream had been degraded and polluted by organic substances.

Ecological Integrity Impairment and Habitat Fragmentation for Neotropical Macroinvertebrate Communities in an Agricultural Stream.

The Volcán River watershed in the south Pacific of Costa Rica comprises forests, small urban settlements, cattle fields, and intensive agriculture (mostly pineapple and sugarcane). The ecological integrity and quality of its waters was assessed from 2011–2013 and 2018–2019 by means of physical–chemical parameters (pH, conductivity, temperature, DO, DBO, nitrate, total phosphorus, and pesticide residues) and benthic macroinvertebrate (MI) sampling in eight sites (Volcán, Cañas, and Ángel Rivers, and Peje and Maura streams), resulting in high ecological integrity in all sites except the Peje stream, which is polluted with nitrates and pesticides. Only in this stream was there a marked seasonal variation in the abundance of 16 MI families including Leptohyphidae, Leptophlebiidae, Philopotamidae, Glossossomatidae, and Corydalidae, among others, whose presence was limited exclusively to the dry season (December to April), disappearing from the stream in the rainy season, with corresponding peaks in nitrate (max 20.3 mg/L) and pesticides (mainly herbicides and organophosphate insecticides). The characteristics of the watershed, with large areas of forest and excellent water quality, allow for the re-colonization of organisms into the Peje stream; however, those organisms are incapable of development and growth, providing evidence of a contaminant-driven habitat fragmentation in this stream during the rainy season.

Effect of anthropogenicity on the temporal diversity and abundance of macro-invertebrates in Calabar River, Okomita, Cross River State, Nigeria

The influence of anthropogenicity on the abundance and diversity of macro-invertebrates was investigated in Calabar River, Okomita, Cross River State for a period of 24 months (August, 2014-September, 2016) in six sampling stations. Bank root macro-invertebrates were collected by kick sampling while substrata macro-invertebrate samples were collected with a van-Veen grab. Seasonal variations in the values of the macro-invertebrates abundance were determined by pooling together the values for the wet and dry seasons. The difference in values in the six stations in each season was tested for significant difference (p < 0.05) while the pooled differences in the two seasons were tested using unpaired (independent) student’s t-test. Spcies diversity was estimated using the Shannon-Wiener index (H’), species richness (d) and evenness (J) of individual distribution among species. All macro-invertebrate groups had highest percentage abundance in the dry season months. Seasonal percentage abundance of insects was significantly different (p˂0.05). Higher seasonal abundance of the total macro-invertebrates was recorded in the dry season and the seasonal variation was significant (p˂0.05). Lower number of pollution intolerant species of macro-invertebrates (Sudanonautes africanus, Orectochilus orbisonorum, Dineutus discolour, Phaon iridipennis, Pila ovata, Natica flammulata and Eulima fischeri) recorded during the rainy season was an indication that the river was more perturbed during the rainy season as a result of influx of pollutants from refuse dumps, farmlands, Okomita Market, abattoir and mechanic workshop. The results of the PCA revealed that DO, hardness, alkalinity, magnesium and cadmium were the most important parameters influencing the abundance of macro-invertebrates in Calabar River, Okomita. Intermediate values and values less than one of Shannon-Weiner diversity index were observed, indicating that Calabar River, Okomita is moving from moderately polluted state to severely polluted condition.

Family-Level Bio-Indication Does not Detect the Impacts of Dams on Macroinvertebrate Communities in a Low-Diversity Tropical River

The Ruzizi River, the outlet of Lake Kivu in the Albertine Rift, flows into Lake Tanganyika and is important for hydropower generation and irrigation. The impacts of 2 dams in the Ruzizi River on macroinvertebrate community composition and diversity were surveyed every 3 months from December 2015 to October 2017. Macroinvertebrate samples were collected at sites upstream and downstream and additionally at two sites further downstream of the dams, in both comparatively pristine and highly disturbed areas. Several indices (Shannon-Wiener index, Simpson index, Pielou’s evenness, Rare Family Prevalence, and Average Score Per Taxa) were used to determine the alpha diversity and evenness of macroinvertebrates at the family level. Our results showed little to no immediate effect of the dams on macroinvertebrate diversity. Macroinvertebrate composition differed slightly below the dams compared to upstream. Communities near Dam II had slightly higher diversity compared to Dam I, probably because the vicinity to Lake Kivu has an immediate effect on diversity upstream of the first dam and likely because Dam II is 30 years younger than Dam I. This study suggests the importance of using species-level indices to better understand the ecological impacts of dams on macroinvertebrate diversity of tropical rivers with low species diversity.

Directional spatial processes override non-directional ones in structuring communities of lotic macroinvertebrates differing in dispersal ability

Dispersal is an essential natural process that influences community assembly, yet directional dispersal through wind and water may have distinctive effects. Environmental and spatial factors jointly influence community structure, but their relative importance is anticipated to vary with spatial distance, dispersal mode, and season. Accordingly, a systemic survey was conducted in subtropical Chinese mountain lotic systems to distinguish the relative contributions of environmental control and spatial structuring upon communities of macroinvertebrates with different dispersal ability. Macroinvertebrate samples were collected from the upper reaches and five tributaries of the Hanjiang River in October 2017 (autumn) and April 2018 (spring). These macroinvertebrates were identified and classified into three dispersal groups: aquatic passive (AqPa), terrestrial passive (TePa), and terrestrial active (TeAc). Variation partitioning analyses were performed on environmental factors and different sets of spatial factors (overland dispersal: Overland, directional downwind dispersal: AEM_Wind, along watercourse dispersal: Watercourse, and directional downstream dispersal: AEM_Water). Findings showed that both environmental filtering and spatial structuring influenced the structure of macroinvertebrate metacommunities. For AqPa and TePa groups, pure environmental effects were stronger than pure spatial effects based on most distance matrices; however, in AEM_Water, the effects of spatial processes surpassed those of environmental filtering. For TeAc group, the role of environmental control and spatial structuring varied depending on different spatial models. The results also highlighted seasonal shifts in metacommunity structuring processes. Spatial structures featuring direction, especially AEM_Water, were predominant in explaining the construction of macroinvertebrate communities. This work suggests that directional dispersal should be explicitly considered when examining the structure of ecological communities.