Abstract
Diversity of amphihaline species in the southwest of the Indian Ocean On the islands of the Indian Ocean the freshwater biodiversity is basically made up of fish (61) and macro-crustaceans (22). The majority of these species are amphihaline: they all live in freshwater, some reproduce there, and they all have the particularity of going through an oceanic larval stage. Some originate from one island or archipelago, others are largely dispersed throughout the entire Indo-Pacific. The communities of amphihaline species have the possibility to maintain a very important flux of larva between the islands, archipelagos, or even the oceanic regions, which gives their population a regional panmictic structure that is quite remarkable. These species have an economic role that is locally important: elvers (eel larva), bichiques (Sicydinae larva) and camarons (Palaemonidae larva) are exploited as a source of protein and, in the west of the Indian Ocean, significant speculation on the exploitation, commerce and development of eel aquaculture is emerging (Mozambique, South Africa, Madagascar). The islands surrounding Madagascar shelter a freshwater biodiversity and knowledge about its functioning is starting to grow (contribution of precedent programmes: ECOFOR, INTERREG 3). Nonetheless, the role of this Madagascan island-continent remains unknown. What are the roles of the recent insular volcanic systems in relation to the African continent and Madagascar, in the regional production of larva that gathers in the estuary? Where are the areas that are the source of biodiversity of these amphihaline species? How do these species disperse themselves in the habitats of different freshwater systems in Madagascar? How do their populations organize themselves in response to growing environmental pressure? How should these resources be managed in a context of sustainable development? The DIAMSOI project proposes, in four parallel work-packages (WP), to make an inventory of the diversity of amphihaline species in some Madagascan regions and establish the importance of Madagascar for the dynamics of these exploited stocks: WP1: Inventory of biodiversity among amphihaline species in the Madagascan systems, comparison with data already collected in the Seychelles, the Comoro Islands and the Mascarene Islands; WP2: Satellite sensing and space conditioning; WP3: Functioning and dynamics of populations: the importance of Madagascan water streams; WP4: Management and preservation, network of estuarial observation Transversal WP: Project animation, organisation of restitution seminars. The study will focus on two types of water streams in Madagascar (a large drainage basin in the west, the Mangoro, and some small size drainage basins in the extreme northwest of the island) and a type of water stream of a high volcanic island (continuation of the actual monitoring on the Reunion). In addition to the inventory mission, a follow-up of the inventory of estuarial post-larva in three types of system will be set up. The combination of field data, analysis of population dynamics and the large-scale satellite sensing will make it possible to clarify the regional functioning of populations, the role held by Madagascar, and to understand the freshwater biodiversity of the islands in the Indian Ocean from a functional point of view. This project will be the occasion to co-frame a thesis between the Fishery Institute of Toliara and the National Museum of Natural History in Paris, and will link teams that are already involved in this topic. The seminar of final restitution will take place in Madagascar.
France