Biodiversité et gestion des systèmes aquatiques continentaux Biodiversity and management of inland aquatic ecosystems

Résumé

La biodiversité des eaux continentales se caractérise par une forte endémicité de nombreuses espèces résultant de la nature insulaire des milieux. Alors qu'elles n'occupent que 1-2 % des terres émergées une proportion importante de vertébrés (environ 1/3) vit dans les eaux continentales ou en dépendent étroitement pour réaliser leur cycle biologique. Certains systèmes aquatiques, comme les lacs dits anciens, sont de véritables laboratoires naturels pour étudier l'évolution, et il faut protéger ce patrimoine.

Les recherches sur l'origine et la dynamique de la biodiversité aquatique (inventaire, phylogénie, biogéographie) doivent se poursuivre, notamment pour les milieux tropicaux encore mal connus. Les relations fonctionnelles entre les espèces et les écosystèmes constituent un nouveau centre d'intérêt qui nécessite à la fois de revisiter les résultats déjà obtenus, de mettre en place des recherches spécifiques, et de développer des approches expérimentales. Quelles relations existent-ils entre la biodiversité et la stabilité ou la productivité des écosystèmes par exemple ?

La biodiversité est un médiateur entre les systèmes écologiques et les systèmes sociaux dont la conservation s'inscrit dans la problématique du développement durable. La valorisation économique de la biodiversité pose de nouvelles questions à l'économie de l'environnement malgré les difficultés méthodologiques rencontrées. Les questions qui intéressent les gestionnaires portent principalement sur l'état de santé des écosystèmes et les moyens de la caractériser (indicateurs biologiques par exemple). La gestion durable des ressources vivantes, et une meilleure évaluation des conséquences des introductions d'espèces (biomanipulations) constituent également des objectifs finalisés auxquels les recherches dans le domaine de la biodiversité aquatique se doivent d'apporter des éléments de réponse.

Mots-clés:

• Biodiversité,
• systèmes continentaux,
• développement durable,
• rôle fonctionnel,
• indicateurs biologiques,
• valeur économique,
• biomanipulations

Abstract

As a result of their island-like nature, inland waters are usually characterised by a high level of endemicity for several animal groups. This patchy distribution also results in great genetic variability between populations. While inland waters occupy only 1-2 % of emerged lands an unusual high proportion of vertebrates (around 1/3) inhabits or is strongly dependant on inland waters to complete their biological cycle. This remarkable concentration of vertebrate biodiversity is also extremely vulnerable, given that inland water aquatic resources world-wide have undergone severe deterioration.

The fragility of inland water ecosystems and their species has been recognised all over the world. These resources have been exposed to a variety of increasing pressures such as water extraction for domestic, agricultural and industrial uses, pollution (organic and inorganic), fishing, introduction of exotic species, habitat alterations in relation to water management, etc. These stressors to the inland water environments have affected, and will continue to affect life in all inland water ecosystems. One of the major causes of change in biodiversity has been, and most likely will continue to be long-term, climate change.

More knowledge is needed about the identification of species, how biological diversity is distributed, and what the trends observed on the short- to long-term biodiversity changes are.

In many tropical countries there are lakes and rivers lacking even the most basic research on fauna and flora. Pertinent information on biological diversity in most developing countries, when it exists, is too sparse or scattered to be of practical use. Therefore, efforts should be devoted to the development of computer data bases and information networks for the collection and storage of information dealing with the identification and distribution of freshwater biodiversity. Development of these systems would benefit from the expertise and collaboration of taxonomists all over the world.

From the perspective of sustainable development, multiple-use management of aquatic ecosystems can provide the framework for achieving long-term sustainability of resources and for maintaining biodiversity. The future of biodiversity is closely linked to the management options at the watershed scale and a key issue is to promote an integrated basin management approach of aquatic. However, a wise management of aquatic systems and the conservation of their biodiversity requires not only technical inputs, but also a good knowledge of social and economic issues. Valuation is a fundamental step in informing planners and resource managers about the economic importance of biodiversity in national development objectives, and to demonstrate the importance of different areas for the biological resources they contain. Research programs have also to be intensified on the complex relationships between biodiversity and aquatic ecosystems functioning which are still poorly understood. Some major ecological issues have been identified : how is system stability and resilience affected by species diversity, and to what extent could the integrity and sustainability of ecosystems be maintained in spite of species deletions resulting from degradation of environmental conditions ? The relationship of species richness to such processes as biological productivity is still an open question.

The key to successful monitoring programs is to maintain the ability to detect general changes in the status of biodiversity and to identify tools that are adequate and appropriate for assessing the effectiveness of measures taken for the conservation of biodiversity through the sustainable use of aquatic systems. A variety of indicators of biological diversity in aquatic systems have been developed and may be employed. The precautionary principle, as adopted for fisheries by FAO, emphasises growing awareness that fisheries management cannot be seen in isolation and must fit an integrated context which satisfies the requirement both for long-term resource sustainability and environmental conservation.

An understanding of the effects of invading exotic organisms on freshwater systems should receive high priority in regard to their documented consequences on native biodiversity in ecosystems where they have been introduced. The knowledge required relates primarily to predictable effects of introduced species.

Keywords:

• Biodiversity,
• inland waters,
• sustainable development,
• functional role,
• bioindicators,
• value of biodiversity,
• biomanipulations