Brachionus falcatus and Platyias patulus indicating organic pollution in Ouémé River’s basin, Republic of Benin

Zooplankton is a biological compartment widely used in the bio-monitoring of aquatic ecosystems. It allows early detection of environmental disturbances even before reaching the upper compartments of interest to humans. The present study evaluated the ability of two rotifer species Brachionus falcatus and Platyias patulus to indicate organic pollution in the Ouémé River basin. Sampling was done between October 2014 and September 2015. Plankton net of 20 μm mesh size was used. Parameters such as NH4+, NO2- and PO43- were measured in water and used for the calculation of the Organic Pollution Index (IPO). The results showed that the occurrence of B. falcatus and P. patulus was 96.66% and 81.11%, respectively. Both species were particularly abundant in sites such as Kaboua and Vossa as well as downstream of the basin (Agonlin-lowé and Bonou). These strong abundances are linked to a very strong organic pollution in Kaboua and Vossa then to a high organic pollution at downstream. The least organically polluted station (Kpassa) had the lowest abundance of both species. B. falcatus and P. patulus are therefore two indicator species of organic pollution in the Ouémé River’s basin in Benin

Composition and structure of phytoplankton community in Ouémé River basin, Republic of Benin

This study aimed to assess the composition and structure of floating phytoplankton assemblage in Ouémé basin. Phytoplankton samples were collected monthly from October 2014 to September 2015. Quantitative samples were taken with a horizontal Van-Dorn sampler and 20 μm mesh plankton net was used for additional qualitative sampling. Microscopic observation of phytoplankton allowed identification of 208 species including 70 Bacillariophyta species, 58 Chlorophyta species, 24 Charophyta species, 21 Euglenophyta species, 18 Cyanophytes species, 9 Phyrrophyta species, 5 Ochrophyta species and 3 Cryptophyta species. The Shannon diversity index varied from 2.4 bit.ind-1 and 3.1 bit.ind-1 showing a relatively good diversification of the community. The population appears largely dominated by 14 species which represent 83.8% of the total phytoplankton. Aulacoseira granulata and Euglena gracilis were the most predominant species with respectively 40.17% and 15.91% relative abundance. Regarding the horizontal pattern of phytoplankton abundance, downstream stations have the greatest abundances. So, the results suggest that downstream stations are richer in phytoplankton which structure differs from that in upper stations.

Composition and seasonal variation of phytoplankton community in Lake Hlan, Republic of Bénin

Knowledge of biodiversity of aquatic ecosystems is nowadays a challenge for global research. Phytoplankton being very important in the sustainability of ecosystems, its mastery allows the development of early monitoring and evaluation tools of the health status of aquatic environments. The study aims to make an initial inventory of phytoplankton of the lake Hlan and to evaluate the influence of hydrologic season on its dynamics. Plankton samples were collected monthly between May and December 2012 using plankton net of 30 µm size. They were then treated and species identified using light microscopy. 39 species in 7 classes (Bacillariophyceae, 18 species in 10 genera), (Cyanophyceae, 5 species in 5 genera), (Chlorophyceae, 5 species in 3 genera), (Zygnematophyceae, 3 species in 2 genera), (Trebouxiophyceae, 2 species in 2 genera) (Euglenophyceae, 4 species in 3 genera) and (Dinophyceae, 2 species in 2 genera) have been identified. The Shannon index varied between 4.8 and 5.1 bit cell-1. This shows that the ecosystem is balanced. Nevertheless, the presence of potentially toxic species requires a monitoring program for Lake Hlan

Identification of characteristic zooplankton species in the Kinyankonge River basin, Burundi

The objective of this study is to determine the zooplankton species that characterize the Kinyankonge River basin in Burundi. Thus, zooplankton was sampled monthly over a period of 18 months (from July 2015 to June 2016, then from January 2017 to June 2017) at seven stations. The Indicator Value (IndVal) of the identified zooplankton species and the coverage of stations were determined. The results showed that three species characterized significantly the most upstream station whereas the water of the irrigation channel was characterized by 4 species. The waters of the Nyabagere tributary and the wastewater treatment plant are characterized by 1 and 5 species, respectively. Furthermore, the dry season was characterized by 4 singletons and 13 pairs of species, while the rainy season was characterized by 11 pairs of species. Moreover, the group of upstream stations was characterized by 5 species while 3 species characterized the group of downstream stations. These species highlighted by the indicator value method can be used to characterize stations in the Kinyankonge River and provide information on seasonal changes

Reproduction and embryonic development in the African freshwater prawn Macrobrachium macrobrachion (Herklots, 1851)

The current study aimed to determine parameters and conditions for successful reproduction of Macrobrachium macrobrachion (Herklots, 1851) in a controlled medium and describing its embryonic development. A total of 122 adult specimens were collected from the delta of Ouémé River and stored in polyethylene tanks with 1:2 male-female sex ratio. This broodstock was fed on pelleted food (Biomar Efico) once a day. For the embryogeny monitoring, eggs were sampled each hour through the first two days after spawning and then every 2 hours till hatching. Spawning happened at a mean temperature, dissolved oxygen concentration and pH of 27.80±0.56°C, 5.83±0.45 mg/L and 7.41±0.34, respectively. The eggs incubation meantime was 12±1 days with nine main embryonic development stages. Hatching lasted on the average 21.00±1.94 h and led to larvae with a mean size of 2.30±0.90 mm. Mean fecundity was 13062.4±5489.93 eggs and 14715.2±6108 eggs, respectively for the first and second seasons with a highly significant difference between them. The best hatching rates were obtained with salinities equal to 2 and 4‰. The results constitute the first database for larval breeding of M. macrobrachion species

Geographical variation of the structure and population parameters of the freshwater prawn Macrobrachium macrobrachion (Herklots, 1851) in West African coastal hydrosystems: Insights from Benin

Abstract The freshwater prawn Macrobrachium macrobrachion (Herklots, 1851) is widely exploited in the Oueme Delta and the low Mono in Benin. The structure and population parameters of M. macrobrachion were evaluated to provide accurate scientific information for the better exploitation and rational management of freshwater prawn species in these areas. In Oueme Delta (1928 specimens) and low Mono (1045 specimens), 2973 specimens were sampled by artisanal and experimental fishing and analysed. The prawns were caught between January and December 2016. Total length and total weight were taken from each specimen. Global and monthly size–frequency distributions showed that recruitment in both populations takes place from August to October with a peak in September. The population parameters obtained by analysing frequency data with FiSAT II software (FAO‐ICLARM) showed an L∞ = 15.50 cm, K = 0.35 year−1, t0 = −0.56 year in Oueme Delta and L∞ = 15.30 cm, K = 0.45 year−1, t0 = −0.43 year in low Mono. The growth performance index (Φ′) was 1.93 and 2.02 for the Oueme Delta and low Mono populations, respectively. The exploitation rates (Emax and E0.5) suggest that more than half of the M. macrobrachion population was exploited in the two areas. Natural and fishing mortality rates showed that both populations of M. macrobrachion were vulnerable to natural and fishing death. The estimated first capture size (Lc) revealed that the majority of the two populations of M. macrobrachion were captured before they reached the size at first sexual maturity (L50), reflecting fishing pressure on small individuals and growth overfishing in both areas. These results showed that the used fishing gears and the fishing frequencies in both areas did not allow the majority of the prawn to grow and reproduce at least once before being caught

Structure and seasonal dynamics of phytoplankton and zooplankton in Lake Azili, small Lake of the pond of River Ouémé, “Benin”

The early reaction of the plankton communities to environmental changes makes it a useful tool for monitoring the pollution of aquatic environments. Lake Azili is a small water body, the majority of which is strongly influenced by river Ouémé during the floods time. Its ecosystem is one of the most important for the country, due to its rich biodiversity, especially that of halieutics. By following the evolution of its health, due to the strong anthropological pressure, this study aims to estimate the structure and the dynamics of its planktonic biodiversity and to assess its current state. It was carried out for seven months between May to November, 2012, according to the hydrological seasons of Benin. Plankton samplings were monthly, taken in a vertical sense from the lake, from all depths, using plankton net. The diversity indices were calculated for the compartment of zooplankton, that of phytoplankton being a preliminary evaluation. A total of 51 species of phytoplankton and 36 zooplankton species were inventoried. Instability is observed in the seasonal structure of both communities, especially for the period of transition between the floods and the floods recession. Due to the specific composition and the diversity, the ecosystem of Lake Azili is perturbed

Diversity and seasonal variation of zooplankton of Lake Hlan, Republic of Bénin (West Africa)

Objective: This study is the first assessment of zooplankton community of the Lake Hlan. It aims to assess zooplankton diversity through hydrological season.Methods and Results: It was carried out from May to December 2012. Monthly  plankton harvesting were performed, using plankton net of 30->m mesh. Three  vertical samplings through the Lake body depth were done at each station and mixed to have a composite sample. Environmental parameters were also assessed at the same time. The zooplankton diversity founded was composed of 45 species (33 rotifers, 6 cladocera and 6 copepods). The community was highly diversified and characteristic of balanced ecosystem. The Shannon diversity index values were ranged between 4.4 bit.ind-1 and 5.1 bit.ind-1. The taxonomic composition and thespecies abundance are affected by the flood coming, when the upstream station is different from the two other at the biological level.Conclusion: The zooplankton community of Lake Hlan has low specific richness, but has very good diversity index across hydrological seasons. Its ecosystem is then lowly affected by anthropological factors. The Lake Hlan currently continues to be a reference ecosystem in ecological status evaluation in Benin republic, since itslocalization has low accessibility.Keywords: Biodiversity; Community structure; Hydrological season; Zooplankton Diversité et variation saisonnière du zooplancton du lac Hlan, République du BéninObjectif: Cette étude est la première évaluation de la communauté zooplanctonique du lac Hlan. Il vise à évaluer la diversité du zooplancton au travers des saisons hydrologiques.Méthodes et résultats: L’étude a été réalisée de Mai à Décembre 2012. Le plancton a été mensuellement échantillonné sur trois stations représentants le plan  horizontal du lac. Un filet à plancton conique de 30 >m de vide de maille a été  utilisé. Un échantillonnage vertical sur toute la colonne du plan d’eau a été réalisé àchaque station. Les paramètres environnementaux ont également relevés. Un total de 45 espèces de zooplancton était identifié (33 rotifères, 6 cladocères et 6  copépodes). La communauté était très bien diversifiée et caractéristique  d'écosystème équilibré. La valeur de l'indice de Shannon a varié entre 4,4 bit.ind-1 et 5,1 bit.ind-1. La composition taxinomique et l'abondance des espèces ont été affectées par la venue de la crue, alors que la station en amont était différente des deux autres au niveau biologique.Conclusion: La communauté zooplanctonique du lac Hlan a une faible richesse  spécifique, mais a un bon indice de diversité à travers les saisons hydrologiques. L’écosystème est alors faiblement affecté par des facteurs anthropologiques. Le lac Hlan continue actuellement d'être un écosystème de référence dans l'évaluation de l'état écologique en république du Bénin, sa localisation étant faiblement accessible.Mots-clés: Biodiversité; Saison hydrologique; Structure d’assemblage; zooplancto