Biological assessment of aquaculture effects on effluent-receiving streams in Ghana using structural and functional composition of fish and macroinvertebrate assemblages

Assessment of functional feeding groups (FFG) structure of aquatic insects in North- western Rif - Morocco

The involvement of trait-based approaches is crucial for understanding spatial patterns, energy flow and matter transfer in running water systems, which requires consistent knowledge of the functional structures of aquatic communities, with the advantage of combining physical properties and behavioral mechanisms of food acquisition rather than the taxonomic group. The present study indicated how functional feeding groups may be used as a proxy for classical taxonomic evaluation, as well as the potential interest in incorporating them as indicators of anthropogenic stressors. The composition and abundance of the functional feeding groups of aquatic insects were examined from September 2021 to August 2022 along the Western Rif Region. Benthic samples were collected from nine sampling points in the studied area using a Surber sampler with a mesh size of 500 µm and a diameter of 20*20 cm. The stations included in this work were chosen for their accessibility as well as their position on the hydrographic systems. The abundance of sampled aquatic organisms in the whole study area revealed 5,342 individuals belonging to 60 families and seven orders of aquatic insects, classified into five feeding functional groups. In terms of abundance, Collector-gatherers (Ephemeroptera and Diptera) were the most abundant trophic group at most of the sites, with a proportion of 38.47%. Predators (Coleoptera, Hemiptera and Odonata) were the second group at all sites, followed by Collector-filters, accounting for 39.53%, 28.14% and 22.37% respectively, while Scarpers and Shredders had the lowest representation across all sites with 4.16%. The high number of registered Collectors could be related to their ability to feed on a diverse range of food items compared to the remaining trophic guilds. According to the Canonical Correspondence Analysis results, physicochemical (i.e. T, pH, BOD₅, Cl- and NO₃-) and hydromorphological (i.e. current velocity and depth) variables were amongst the key predictors of shaping the functional structure of aquatic biota during this investigation. It is highly recommended to carry out suitable measures to largely attenuate anthropogenic pressures in order to preserve the integrity of freshwater bodies and their biota.

A benthic invertebrates-based biotic index to assess the ecological status of West African Sahel Rivers, Burkina Faso

Conserving aquatic resources in the West African Sahel requires water management tools to assess the ecological status of surface water bodies threatened by mounting pressures from agricultural intensification and urbanization. Macroinvertebrate communities of Sahelian rivers were examined to test if a multi-metric index approach could be developed to assess the ecological quality of rivers. A total of 40 sample sites falling within a continuum ranging from "unimpaired reference sites" to "impaired sites" were assessed during this study. Macroinvertebrates were sampled with a hand net following a multi-habitat sampling approach. Key environmental parameters, both physico-chemical and hydro-morphologic, were recorded. More than 20 candidate metrics were evaluated in four categories: composition, functional feeding, diversity, and tolerance. We used detailed analysis procedures to exclude unsuitable metrics from the data set. After excluding redundant metrics, six-core metrics were selected to compose the Sahel River Multimetric Index (SRMI): Total-taxa, Shannon & Weiner index, EPT-taxa, ASPT-NEPBIOS and ASPT-SASS and Collector-filterers. The final index derived from these metrics was divided into five ecological quality classes (high, good, moderate, poor, and bad). The results showed that the SRMI responded to a set of environmental parameters associated with a gradient of human pressures affecting the ecological integrity of water bodies (R²≥|0.50|; p < 0.05; p < 0.001). This work produced a data base and analysis that confirms the usefulness of an unprecedented and promising tool for biological monitoring and decision-making in Sahelian regions' water management.

Novel use of the alga Pseudokirchneriella subcapitata, as an early-warning indicator to identify climate change ambiguity in aquatic environments using freshwater finfish farming as a case study

Aquaculture is one of the fastest growing food producing industries in the world. This dramatic increase in growth has raised many environmental concerns. Evaluation of fish farm effluent is frequently assessed by physicochemical parameters. This approach indicates potential degradation caused by the effluent and not cumulative effects on aquatic ecosystems. This study investigated relationships between physicochemical parameters (temperature, pH, conductivity, nitrogen, phosphorus, oxygen and suspended solids), typically used to assess water quality with the Pseudokirchneriella subcapitata algal bioassay, which evaluated the potential ecotoxicological effects that freshwater fish farm effluent has on its receiving ecosystems and organisms. Influent and effluent samples were collected from a freshwater farm facility every two weeks from April 2018 to October 2018 in the Republic of Ireland. This monitoring period coincided with one of the warmest and driest periods recorded by meteorological stations in the Republic of Ireland. Physicochemical analyses were found to be similar to those in other farm studies. After exposure of algae to the effluent, stimulation of algal growth rates increased by >50%. This stimulation was observed during periods of increased temperatures which were as a result of heat wave and drought conditions experienced during monitoring. Correlation studies identified a moderately strong relationship between algal stimulation and temperature (r = -0.619). This study discovered that removal of Lemna minor (aquatic plant), impacted strongly on the freshwater farm pond-process to cope with nitrates. The constructed wetland system was unable to efficiently treat nitrates and phosphates during conditions of drought. These findings indicate that standard water quality parameters may not be applicable to inform appropriate suitability of fish farm effluent for discharge to receiving water. The research conducted in this study has suggested a potential toolbox that includes P. subcapitata may provide an early warning system for adverse effects as a result of climate change.

Detection of environmental impacts of shrimp farming through multiple lines of evidence

In order to evaluate the impact of semi-intensive shrimp farming, comparisons between Control and Impact areas were made based on multiple lines of evidence using an asymmetrical design. Water and sediment samples were collected in four shrimp farms located in Todos os Santos Bay, Bahia, Brazil. Nutrients, trace elements and macrobenthic assemblages were evaluated using uni- and multivariate analyzes. Significant differences were observed between Impact and Control areas for the water column dataset (i.e., ancillary variables, SPM, dissolved nutrients and major and trace elements in SPM), whereas no significant differences were observed for the chemistry of sediments. Macrobenthic assemblages were negatively affected by shrimp farm activities. Impacted sites presented the lowest abundance, richness and different structure of macrofaunal benthic assemblages. Farms clearly produced negative impacts in the Todos os Santos Bay. This conclusion was only possible to be reached through the use of multiple lines of evidence. Chemistry and benthic assemblages data combined produced a better description of the quality and impacts of the evaluated environments. Different conclusions would have been reached if chemistry and ecology results were studied separately vs. together.

Assessment of benthic macroinvertebrates at Nile tilapia production using artificial substrate samplers

Biomonitoring is a cheap and effective tool for evaluation of water quality, and infer on the balance of aquatic ecosystems. The benthic macroinvertebrates are bioindicators sensitive to environmental changes, and can assist in detecting and preventing impacts such as organic enrichment and imbalance in the food chain. We compared the structure of benthic communities on artificial substrate samplers located in places near and far from net cages for production of Nile tilapia (Oreochromis niloticus). Samplers were manufactured with nylon net, using substrates such as crushed stone, gravel, loofah and cattail leaves. Samples were collected after 30 days of colonization, rinsed and then the specimens were identified and quantified. The following metrics were calculated: richness of Operational Taxonomic Units, Margalef richness, abundance of individuals, Shannon index and evenness index. The macrobenthic community structure was strongly modified according to the proximity of the net cages. Metrics showed significant differences (p < 0.05) between near and distant sites, for both periods (dry and rainy seasons). The position of the samplers significantly affected the structure of macroinvertebrate community, as near sites showed higher values for the community metrics, such as richness and diversity. Near sites presented a larger number of individuals, observed both in the dry and rainy seasons, with a predominance of Chironomidae (Diptera) in the dry season and Tubificidae (Oligochaeta) in the rainy season.