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 World's water and approximately 0.8% of the Earth's surface, yet this tiny fraction of global water supports at least 100000 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'.

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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.

Neurotransmitter release involves the assembly of a heterotrimeric SNARE complex composed of the vesicle protein synaptobrevin (VAMP 2) and two plasma membrane partners, syntaxin 1 and SNAP-25. Calcium in¯ux is thought to control this process via Ca 2+ -binding proteins that associate with components of the SNARE complex. Ca 2+ /calmodulin or phospholipids bind in a mutually exclusive fashion to a C-terminal domain of VAMP (VAMP 77±90 ), and residues involved were identi®ed by plasmon resonance spectroscopy. Microinjection of wild-type VAMP 77±90 , but not mutant peptides, inhibited catecholamine release from chromaf®n cells monitored by carbon ®bre amperometry. Pre-incubation of PC12 pheochromocytoma cells with the irreversible calmodulin antagonist ophiobolin A inhibited Ca 2+ -dependent human growth hormone release in a permeabilized cell assay. Treatment of permeabilized cells with tetanus toxin light chain (TeNT) also suppressed secretion. In the presence of TeNT, exocytosis was restored by transfection of TeNT-resistant (Q 76 V, F 77 W) VAMP, but additional targeted mutations in VAMP 77±90 abolished its ability to rescue release. The calmodulin-and phospholipid-binding domain of VAMP 2 is thus required for Ca 2+ -dependent exocytosis, possibly to regulate SNARE complex assembly. Keywords: neuroendocrine cells/secretory vesicle/ SNARE/tetanus toxin IntroductionNeurones and neuroendocrine cells release transmitters and neuropeptides by calcium-dependent exocytosis of the contents of vesicles docked at the plasma membrane. This process requires assembly of trimeric SNARE complexes formed by the vesicle-associated membrane protein synaptobrevin (VAMP 2) and two partners that are expressed mainly in the plasma membrane, syntaxin 1 and synaptosome-associated protein of 25 kDa (SNAP-25) (reviewed by Jahn and Sudhof, 1999;Lin and Scheller, 2000;Mayer, 2001). Analysis of a minimal complex composed uniquely of the interacting domains of these three proteins has revealed a parallel bundle of four a-helices (one from VAMP 2, one from syntaxin 1 and two from SNAP-25) twisted into a superhelical structure (Sutton et al., 1998). Extrapolation of these data to a situation in which VAMP 2 and syntaxin 1/SNAP-25 are anchored in distinct lipid bilayers (i.e. docked vesicle membranes and plasma membranes, respectively) led to a proposal for trans SNARE complex function. The zippingup of SNARE complexes from the N-terminus to the C-terminus would pull the opposing C-terminal transmembrane anchors towards each other and promote membrane fusion at the vesicle±plasma membrane interface.Abundant evidence from the use of botulinum and tetanus toxins (BoNT and TeNT, respectively), which inhibit transmitter release by cleaving SNARE proteins (Xu et al., 1998;Hua and Charlton, 1999), as well as mutagenesis in invertebrates and mice (Fergestad et al., 2001;Schoch et al., 2001;Washbourne et al., 2002), have consolidated the view that SNARE proteins are required for exocytosis. However, the precise role of SNARE complex assembly in membr...