Biodiversité et relations trophiques dans quelques milieux estuariens et lagunaires de l’Afrique de l’Ouest : Adaptations aux pressions environnementales
Year: 2004
Type: dissertation
Abstract: This work is the result of a research on West African estuaries and lagoon ecosystems: estuaries of Sine-Saloum (Senegal) and the Gambia, (The Gambia), as well as the lagoons Ébrié (Ivory Coast) and Lake Nokoué (Benin). Estuaries and lagoons are highly productive and economically important ecosystems and are among those threatened as their biodiversity and productivity are constant exposed to various disturbances. These disturbances can weaken the stability and durability of these ecosystems. This led to the problematic raised in the thesis: To approach the African western ecosystems and the environmental pressures that they undergo that eventually affect the biodiversity and the trophic relations of their aquatic living resources. \n\n\tThis work seeks to offer a precise analysis of the fish assemblages and to evaluate how the environmental changes affect the populations of brackish waters. It is necessary to integrate information on several water collections to arrive to a more complete comprehension of such ecosystems. The complex circumstances and strongly variables leading to situations of stress require a complete comprehension of the operation of these ecosystems. First, the concept of stress environmental, as well natural and/or human-related is presented. This demands the identification of the environmental factors which affect the dynamics and the interactions between the various biological compartments in order to explain the varying conditions of the ecosystems. After having presented each ecosystem and their respective aquatic resources, the author exposes the methodologies used for the analyses, as well employing ecological statistical analyses of populations based on experimental or collective fishing surveys to study the trophic relations existing within systems. The trophic interactions in these ecosystems were studied and compared in relation to various aspects of the environmental stress based on various ecological methods, supplemented by statistical analyses in particular the method of the comparison of abundance and the not supervised biomass (ABC) and neural networks (ANN), associated has a model trophodynamics, Ecopath. Complementary statistical ecological analyses such as not supervised analyses facilitated our analysis by defining the roles of the various groups and the intensity of the interactions between species which contribute to stabilize the ecosystems. The results obtained starting from the statistical studies highlight the differences in fish species assemblages according to in each ecosystem. The results starting from Ecopath indicate principal flows of energy among groups and raise interesting questions about the ecological concepts of stability and maturity of the ecosystems. The importance of detritus as support of the food chains is observed, especially in the event of limit of the primary production and even of the other sources of food. A reversed hypersalinity installed following Sahel drought in an estuary (Sine-Saloum), appears less harmful with the biodiversity than the effects of severe human activity diversified in a Beninese lagoon. The trophic relations appear based on the primary production in two ecosystems while detritus-based in the two others. The food sources of fish are not all fully utilized. The output of fishing activity and the biomass of the target groups are variable under the constrains of the ecosystem effect just like of the fishing effort itself. The convergence of the results concerning the biodiversity and the trophic relations in expressing terms of environmental stress is discussed in a final chapter. This is also a general conclusion and an outline of proposals for future research and management for a durable management of the resource. The significance of these ecosystems depends on the diversity of the habitats which play a part as refuge, feeding zone of food and access of migration that allows, in return, the survival of large populations. These habitats vary from the geographical point of view and by the environmental conditions which have effects over the aquatic communities and consequently on their contribution to the local economy. The comparison of geographically close ecosystems offers possibilities of generalization even if certain distinctive features especially make each ecosystem single as for its biological structure. This type of study is necessary for future management and conservations.\n\n\t\nKeywords : West Africa ; Biodiversity ; Trophic relations ; Adaptation ; Quantitative ecology ; System maturity
Author: Maria Ching Villanueva
Language: French
Subfield: Aquatic Science
Domain: Life Sciences
SDG: Life below water
Open Access status: green
OpenAlex ID: W2128122678