No abstract

The benthic macroinvertebrates of Aby lagoon (West Africa: Ivory coast) was studied during four seasons (high dry season, high rainy season, low dry season and low rainy season, respectively) from June 2006 to March 2007. The distribution of the benthic macroinvertebrates species was recorded at 13 stations on the whole of the lagoon. A total of 62 taxa of benthic macroinvertebrates belonging to 28 families and 10 orders were listed. The molluscs and crustaceans dominate qualitatively by adding up 51 and 24%, respectively of the total number of organisms. Five taxa (Corbula trigona (20%), Pachymelania aurita (12%), Clibernhardius cooki (7%), Oligochaeta (7%) and Crassostrea gasar (6%) accounted for 52% of total abundance. Classification analysis used to perform the characterisation of the lagoon on the basis of benthic macroinvertebrates showed the existence of four main clusters in which the seasonal pattern in benthic macroinvertebrates were very similar in the four seasons. In contrast the species richness and diversity indices were significantly different. Furthermore these indices where higher in the stations closer to the sea and surrounded by mangrove trees (southern area) compared to the inland ones.

No abstract

Shrimps are an important component of river invertebrate assemblages in tropical freshwater where they are a controlling group in food webs. In order to determine shrimp diversity in the Banco Basin (Côte d'Ivoire, West Africa) and examine whether the patterns of species distribution were related to environmental conditions, six sites were monitored. Sampling was conducted in 2008 during February, May, September and November using a long-handled net (25-cm diameter, 2-mm mesh). For each site, we measured environmental variables (conductivity, pH, water temperature, dissolved oxygen, turbidity, current speed, and water depth and width). Three shrimp species, Macrobrachium thysi (Powell 1980), Macrobrachium dux (Lenz 1910) and Desmocaris trispinosa (Aurivillius 1898) were identified. D. trispinosa was the largest distributed (more than 50% of occurrence) and the most abundant (67% of total number of specimens caught). It was followed by M. thysi with 47% and 32% of occurrence and abundance, respectively. Canonical correspondence analysis (CCA) showed a spatial distribution of the shrimp community, significantly influenced by width, depth, conductivity, type of substrate, turbidity and dissolved oxygen. Due to the fact that the Banco River hosts an endemic species in Côte d'Ivoire (Macrobrachium thysi), the conservation of integrity of this basin was recommended. canonique des correspondances montre que la distribution spatiale des crevettes dans le bassin du Banco est fortement influencée par la largeur, la profondeur, la conductivité, le type de substrat, la turbidité et l'oxygène dissous. Compte tenu du fait que la rivière Banco héberge une espèce endémique à la Côte d'Ivoire (Macrobrachium thysi), la conservation de l'intégrité de ce bassin est fortement recommandée. RÉSUMÉ

In the present study, a first inventory of benthic macroinvertebrates in the Banco Stream, Côte d'Ivoire, and the correlations between environmental variables and taxonomic richness were analysed. Seven stations were sampled monthly over a 1-year period, using a hand net (10 9 10 cm, 250 lm mesh, 50 cm length). One hundred and thirty-two macroinvertebrate taxa were recorded. These taxa were distributed among 74 families and 15 orders belonging to Insecta (118 taxa; 89% of total richness), Oligochaeta (seven taxa), Crustacea (five taxa) and Mollusca (two taxa). Kruskal-Wallis test revealed significant difference (at least P < 0.05) in macroinvertebrate richness between upstream stations (S1 and S2) and stations S4, S5 and S6. Chironominae and Tanypodinae (Insecta) were the two very frequent taxa in all the stations. Lumbriculidae (Oligochaeta), Desmocaris trispinosa (Crustacea) and Eurymetra sp. (Insecta) were frequently found in the samples. Hierarchical cluster analysis revealed three groups of sampling stations according to taxonomic similarity. Taxonomic richness was significantly and negatively correlated with conductivity, while it was significantly and positively correlated with substrate types (woody debris and gravel). Due to the fact that Banco stream is the locality type of an endemic shrimp species (Macrobrachium thysi), this basin is of high conservation priority.