Christian Lévêque

Freshwater biodiversity: importance, threats, status and conservation challenges

Freshwater biodiversity is the over‐riding conservation priority during the International Decade for Action ‐‘Water for Life’ ‐ 2005 to 2015. Fresh water makes up only 0.01% of the Worlds water and approximately 0.8 % of the Earths surface, yet this tiny fraction of global water supports at least 100 000 species out of approximately 1.8 million ‐ almost 6% of all described species. Inland waters and freshwater biodiversity constitute a valuable natural resource, in economic, cultural, aesthetic, scientific and educational terms. Their conservation and management are critical to the interests of all humans, nations and governments. Yet this precious heritage is in crisis. Fresh waters are experiencing declines in biodiversity far greater than those in the most affected terrestrial ecosystems, and if trends in human demands for water remain unaltered and species losses continue at current rates, the opportunity to conserve much of the remaining biodiversity in fresh water will vanish before the ‘Water for Life’ decade ends in 2015. Why is this so, and what is being done about it? This article explores the special features of freshwater habitats and the biodiversity they support that makes them especially vulnerable to human activities. We document threats to global freshwater biodiversity under five headings: overexploitation; water pollution; flow modification; destruction or degradation of habitat; and invasion by exotic species. Their combined and interacting influences have resulted in population declines and range reduction of freshwater biodiversity worldwide. Conservation of biodiversity is complicated by the landscape position of rivers and wetlands as ‘receivers’ of land‐use effluents, and the problems posed by endemism and thus non‐substitutability. In addition, in many parts of the world, fresh water is subject to severe competition among multiple human stakeholders. Protection of freshwater biodiversity is perhaps the ultimate conservation challenge because it is influenced by the upstream drainage network, the surrounding land, the riparian zone, and ‐ in the case of migrating aquatic fauna ‐ downstream reaches. Such prerequisites are hardly ever met. Immediate action is needed where opportunities exist to set aside intact lake and river ecosystems within large protected areas. For most of the global land surface, trade‐offs between conservation of freshwater biodiversity and human use of ecosystem goods and services are necessary. We advocate continuing attempts to check species loss but, in many situations, urge adoption of a compromise position of management for biodiversity conservation, ecosystem functioning and resilience, and human livelihoods in order to provide a viable long‐term basis for freshwater conservation. Recognition of this need will require adoption of a new paradigm for biodiversity protection and freshwater ecosystem management ‐ one that has been appropriately termed ‘reconciliation ecology’.

Global diversity of fish (Pisces) in freshwater

The precise number of extant fish species remains to be determined. About 28,900 species were listed in FishBase in 2005, but some experts feel that the final total may be considerably higher. Freshwater fishes comprise until now almost 13,000 species (and 2,513 genera) (including only freshwater and strictly peripheral species), or about 15,000 if all species occurring from fresh to brackishwaters are included. Noteworthy is the fact that the estimated 13,000 strictly freshwater fish species live in lakes and rivers that cover only 1% of the earth’s surface, while the remaining 16,000 species live in salt water covering a full 70%. While freshwater species belong to some 170 families (or 207 if peripheral species are also considered), the bulk of species occur in a relatively few groups: the Characiformes, Cypriniformes, Siluriformes, and Gymnotiformes, the Perciformes (noteably the family Cichlidae), and the Cyprinodontiformes. Biogeographically the distribution of strictly freshwater species and genera are, respectively 4,035 species (705 genera) in the Neotropical region, 2,938 (390 genera) in the Afrotropical, 2,345 (440 genera) in the Oriental, 1,844 (380 genera) in the Palaearctic, 1,411 (298 genera) in the Nearctic, and 261 (94 genera) in the Australian. For each continent, the main characteristics of the ichthyofauna are briefly outlined. At this continental scale, ichthyologists have also attempted to identify ichthyological ‘‘provinces’’ that are regions with a distinctive evolutionary history and hence more or less characteristic biota at the species level. Ichthyoregions are currently identified in each continent, except for Asia. An exceptionally high faunal diversity occurs in ancient lakes, where one of the most noteworthy features is the existence of radiations of species that apparently result from intra-lacustrine speciation. Numerous fish-species flocks have been identified in various ancient lakes that are exceptional natural sites for the study of speciation. The major threats to fish biodiversity are intense and have been relatively well documented: overexploitation, flow modification, destruction of habitats, invasion by exotic species, pollution including the worldwide phenomena of eutrophication and sedimentation, all of which are interacting.

The Freshwater Animal Diversity Assessment: an overview of the results

We present a summary of the results included in the different treatments in this volume. The diversity and distribution of vertebrates, insects, crustaceans, molluscs and a suite of minor phyla is compared and commented upon. Whereas the available data on vertebrates and some emblematic invertebrate groups such as Odonata (dragonflies and damselflies) allow for a credible assessment, data are deficient for many other groups. This is owing to knowledge gaps, both in geographical coverage of available data and/or lack of taxonomic information. These gaps need to be addressed urgently, either by liberating date from inaccessible repositories or by fostering taxonomic research. A similar effort is required to compile environmental and ecological information in order to enable cross-linking and analysis of these complementary data sets. Only in this way will it be possible to analyse information on freshwater biodiversity for sustainable management and conservation of the world’s freshwater resources.

Humans transforming the Global Water System

Fresh water figures prominently in the machinery of the Earth system and is key to understanding the full scope of global change. Greenhouse warming with a potentially accelerated hydrologic cycle is already a well-articulated science issue, with strong policy implications. A broad array of other anthropogenic factors—widespread land cover change, engineering of river channels, irrigation and other consumptive losses, aquatic habitat disappearance, and pollution—also influences the water system in direct and important ways. A rich history of site-specific research demonstrates the clear impact of such factors on local environments. Evidence now shows that humans are rapidly intervening in the basic character of the water cycle over much broader domains. The collective significance of these many transformations on both the Earth system and human society remains fundamentally unknown [Framing Committee of the GWSP, 2004].

An assessment of animal species diversity in continental waters

There is a need for monitoring the status and trends of freshwater biodiversity in order to quantify the impacts of human actions on freshwater systems and to improve freshwater biodiversity conservation. Current projects carrying assessment of freshwater biodiversity focus mainly on leading-better-known groups such as fish, or identify keystone species and/or endemic freshwater systems for conservation purposes. Our purpose is to complete these existing projects by providing quantitative estimates of species number for all freshwater groups on each continent and/or major eco-regions. This article present the results of the first implementation phase carried out from September 2002 to June 2003 and which addressed only freshwater animal species. The project consisted of: (1) compiling existing data from literature, web sites and museum collections; (2) contacting scientific experts of each group to provide a ‘to the best of their knowledge, estimates of species numbers. In this study, we consider true freshwater species to be, those that complete part or all of their life cycle in freshwater, and water-dependent species those that need freshwater for food or that permanently use freshwater habitats. The current order of magnitude for known freshwater animal species world wide is 100 000, of which half are insects. Among other groups, there are some 20 000 vertebrate species; 10 000 crustacean species and 5000 mollusc species that are either true freshwater or water-dependant species. The study highlighted gaps in the basic knowledge of species richness at continental and global scales: n n(1) n nSome groups such as Protozoa, nematodes or annelids have been less studied and data on their diversity and distribution is scarce. Because current richness estimates for these groups are greatly biased by knowledge availability, we can expect that real species numbers might be much higher. n n n n n(2) n nContinents are not equal in the face of scientific studies: South America and Asia are especially lacking global estimates of species richness for many groups, even for some usually well-known ones such as molluscs or insects.

Freshwater Animal Diversity Assessment

An introduction to the Freshwater Animal Diversity Assessment (FADA) project.- Global diversity of aquatic macrophytes in freshwater.- Global diversity of sponges (Porifera: Spongillina) in freshwater.- Global diversity of inland water cnidarians.- Global diversity of free living flatworms (Platyhelminthes, Turbellaria) in freshwater.- Global diversity of rotifers (Rotifera) in freshwater.- Global diversity of nemerteans (Nemertea) in freshwater.- Global diversity of nematodes (Nematoda) in freshwater.- Global diversity of hairworms (Nematomorpha: Gordiaceae) in freshwater.- Global diversity of gastrotrichs (Gastrotricha) in fresh waters.- Global diversity of bryozoans (Bryozoa or Ectoprocta) in freshwater.- Global diversity of tardigrades (Tardigrada) in freshwater.- Global diversity of polychaetes (Polychaeta Annelida) in freshwater.- Global diversity of oligochaetous clitellates (Oligochaeta Clitellata) in freshwater.- Global diversity of leeches (Hirudinea) in freshwater.- Global diversity of freshwater mussels (Mollusca, Bivalvia) in freshwater.- Global diversity of gastropods (Gastropoda Mollusca) in freshwater.- Global diversity of large branchiopods (Crustacea: Branchiopoda) in freshwater.- Global diversity of cladocerans (Cladocera Crustacea) in freshwater.- Global diversity of ostracods (Ostracoda, Crustacea) in freshwater.- Global diversity of copepods (Crustacea: Copepoda) in freshwater.- Global diversity of fishlice (Crustacea: Branchiura: Argulidae) in freshwater.- Global diversity of mysids (Crustacea-Mysida) in freshwater.- Global diversity of spelaeogriphaceans & thermosbaenaceans (Crustacea Spelaeogriphacea & Thermosbaenacea) in freshwater.- Global diversity of cumaceans & tanaidaceans (Crustacea: Cumacea & Tanaidacea) in freshwater.- Global diversity of Isopod crustaceans (Crustacea Isopoda) in freshwater.- Global diversity of amphipods (Amphipoda Crustacea) in freshwater.- Global diversity of syncarids (Syncarida Crustacea) in freshwater.- Global diversity of crabs (Aeglidae: Anomura: Decapoda) in freshwater.- Global diversity of crabs (Crustacea: Decapoda: Brachyura) in freshwater.- Global diversity of shrimps (Crustacea: Decapoda: Caridea) in freshwater.- Global diversity of crayfish (Astacidae, Cambaridae, and Parastacidae-Decapoda) in freshwater.- Global diversity of water mites (Acari, Hydrachnidia Arachnida) in freshwater.- Global diversity of halacarid mites (Halacaridae: Acari: Arachnida) in freshwater.- Global diversity of oribatids (Oribatida: Acari: Arachnida).- Global diversity of springtails (Collembola Hexapoda) in freshwater.- Global diversity of mayflies (Ephemeroptera, Insecta) in freshwater.- Global diversity of dragonflies (Odonata) in freshwater.- Global diversity of stoneflies (Plecoptera Insecta) in freshwater.- Global diversity of true bugs (Heteroptera Insecta) in freshwater.- Global diversity of caddisflies (Trichoptera: Insecta) in freshwater.- Global diversity of dobsonflies, fishflies, and alderflies (Megaloptera Insecta) and spongillaflies, nevrorthids, and osmylids (Neuroptera Insecta) in freshwater.- Global diversity of water beetles (Coleoptera) in freshwater.- Global biodiversity of Scorpionflies and Hangingflies (Mecoptera) in freshwater.- Global diversity of non-biting midges (Chironomidae Insecta-Diptera) in freshwater.- Global diversity of craneflies (Insecta, Diptera: Tipulidea or Tipulidae sensu lato) in freshwater.- Global diversity of black flies (Diptera: Simuliidae) in freshwater.- Global diversity of mosquitoes (Insecta: Diptera: Culicidae) in freshwater.- Global diversity of dipteran families (Insecta Diptera) in freshwater (excluding Simulidae, Culicidae, Chironomidae, Tipulidae and Tabanidae).- Global diversity of butterflies (Lepidotera) in freshwater.- Global diversity of hymenopterans (Hymenoptera Insecta) in freshwater.- Global diversity of true and pygmy grasshoppers (Acridomorpha, Orthoptera) in freshwater.- Global diversity of fish (Pisces) in freshwater.- Global diversity of amphibians (Amphibia) in freshwater.- Global diversity of lizards in freshwater (Reptilia: Lacertilia).- Global diversity of crocodiles (Crocodilia, Reptilia) in freshwater.- Global diversity of turtles (Chelonii Reptilia) in freshwater.- Global diversity of snakes (Serpentes Reptilia) in freshwater.- Global diversity of mammals (Mammalia) in freshwater.- Global diversity of freshwater birds (Aves).- The Freshwater Animal Diversity Assessment: an overview of the results.

An introduction to the Freshwater Animal Diversity Assessment (FADA) project

The Freshwater Animal Diversity Assessment (FADA) project aims at compiling an overview of genus- and species-level diversity of animals in the continental, aquatic ecosystems of the world. It is a collective effort of 163 experts, and presents 59 articles treating the diversity and endemism of different animal taxa, ranging from microscopic worms to mammals, at global and regional scales. Given their structural importance, an article on macrophytes is also added. Here, we give an overview of the project’s history, and outline the common framework of the various articles, as well as the conventions the experts agreed to adhere to in their treatises. Furthermore, we briefly introduce future prospects.

Limnologie du fleuve Bandama, Côte d'Ivoire

In recent years, the Bandama river and its catchment area have been subjected to intense limnological research, in the framework of a program of ecological monitoring of aquatic environment, treated with anti-simulium insecticides (W.H.O. project for Onchocerciasis control in West-Africa).The present contribution summarizes the information collected on this tropical river. After a brief description of the basin and its geological setting, climate and hydrology, results of studies on the water chemistry, biology and ecology of its animal and plant communities (plankton, periphyton, insects, decapod crustaceans, fish) are presented. The human impact on the system (dam-building, use of pesticides) is also discussed.

The benthic fauna: ecology, biomass and communities

Benthos consists of all those aquatic organisms which are associated in some way with the bottom sediments. We shall, therefore, consider here only the organisms and communities inhabiting the lake sediments, reserving a study of the periphyton found on higher aquatic plants for a further chapter. This periphyton was far from negligible in Lake Chad where fringing vegetation and submerged water grasses were numerous. It was usually composed of different species to the benthos although some were occasionally found among the benthos when it was sampled close to plant clumps.