Summary 1. Freshwater conservation has received less attention than its terrestrial or marine counterparts. Given the accelerated rate of change and intensive human use that freshwater ecosystems are submitted to, it is urgent to focus more attention on fresh waters. Existing conservation planning tools – such as Marxan – need to be modified to account for the special nature of these systems. Connectivity plays a key role in freshwater ecosystems. Threats are mediated along river corridors, and the condition of the entire catchment influences river biodiversity downstream. This needs to be considered in conservation planning. 2. The probabilities of occurrence of nine native freshwater fish species in a Mediterranean river basin, obtained from Multivariate Adaptive Regression Splines‐ Generalized Linear Model (MARS‐GLM) models, were used as features to develop spatial conservation priorities. The priorities accounted for complementarity and spatial design issues. 3. To deal with the connected nature of rivers, we modified Marxan’s boundary length penalty, avoiding the selection of isolated planning units and forcing the inclusion of closer upstream areas. We introduced ‘virtual boundaries’ between non‐headwater stream segments and added distance‐weighted penalties to the overall connectivity cost (CP) when stream segments upstream of the selected planning units are not selected. 4. This approach to prioritising connectivity is concordant with ecological theory, as it considers the natural and roughly exponential decay of upstream influences with distance. It accounts for the natural capacity of rivers to mitigate impacts when designing reserves. When connectivity was not emphasised, Marxan prioritised natural corridors for longitudinal movements. In contrast, whole sub‐basins were prioritised when connectivity was emphasised. Changing the relative emphasis on connectivity substantially changed the spatial prioritisation; our conservation investment could move from one basin to another. 5. Our novel approach to dealing with directional connectivity enables managers of freshwater systems to set ecologically meaningful spatial conservation priorities.

Principal Component Analysis (PCA) was performed to extract the main gradients of diet composition. Pearson's correlation and T-tests were used to assess the relation between diet characteristics (composition, diversity, taxonomic richness) and geographic and climatic variables. Results:A clear latitudinal gradient in trophic diversity and diet composition is observed. Otter diet is more diverse and features more prey classes in southern localities, while the species is more piscivorous towards the north, where it predates upon a higher number of fish families. This pattern is contrasting when temperate and Mediterranean localities of Europe are compared. Mediterranean otters behave as more generalist predators than temperate ones, relying less on fish, and more on crayfish, aquatic invertebrates and reptiles.Main conclusions: Geographical differences in otters feeding ecology in Europe seem to be related with the two contrasted climatic conditions affecting prey populations. The otter can act as a highly specialised piscivorous predator in temperate freshwater ecosystems, which do not suffer a dry season and are 3 comparatively more stable than Mediterranean ones. However, the unpredictable prey availability in Mediterranean areas, affected by strong spatial and temporal water shortages, would favour a diversification of otter diet. 4

1.We used a basin approximation to analyse distribution patterns of different components of biodiversity (taxonomic richness, endemicity, taxonomic singularity, rarity) and conservation status of freshwater fish fauna in 27 Mediterranean Iberian rivers. 2.Basin area alone explained more than 80% of variation in native species richness. Larger basins featured not only a higher number of native species, but also more endemic and rare species and less diversified genera than smaller ones. 3.In contrast, smaller basins scored higher community conservation values, due to their lower degree of invasion by introduced species. 4.The presence of dams was the most important factor determining the conservation status of fish communities, and it was also positively associated with the number of introduced species. 5.While the most important components of Iberian freshwater fish biodiversity are located in large basins, small unregulated ones feature better conserved fish communities.2

Abstract. Mediterranean endemic freshwater fish are among the most threatened biota in the world. Distinguishing the role of different extinction drivers and their potential interactions is crucial for achieving conservation goals. While some authors argue that invasive species are a main driver of native species declines, others see their proliferation as a co-occurring process to biodiversity loss driven by habitat degradation. It is difficult to discern between the two potential causes given that few invaded ecosystems are free from habitat degradation, and that both factors may interact in different ways.Here we analyze the relative importance of habitat degradation and invasive species in the decline of native fish assemblages in the Guadiana River basin (southwestern Iberian Peninsula) using an information theoretic approach to evaluate interaction pathways between invasive species and habitat degradation (structural equation modeling, SEM). We also tested the possible changes in the functional relationships between invasive and native species, measured as the per capita effect of invasive species, using ANCOVA.We found that the abundance of invasive species was the best single predictor of natives' decline and had the highest Akaike weight among the set of predictor variables examined. Habitat degradation neither played an active role nor influenced the per capita effect of invasive species on natives. Our analyses indicated that downstream reaches and areas close to reservoirs had the most invaded fish assemblages, independently of their habitat degradation status. The proliferation of invasive species poses a strong threat to the persistence of native assemblages in highly fluctuating environments. Therefore, conservation efforts to reduce native freshwater fish diversity loss in Mediterranean rivers should focus on mitigating the effect of invasive species and preventing future invasions.

This paper revises the response of freshwater ostracods to different environmental conditions and anthropogenic impacts, with a worldwide overview of the potential use of these microcrustaceans as bioindicators and several examples of applications in different scenarios. The development of either a single species or an ostracod assemblage is influenced by physical-chemical properties of waters (salinity, temperature, pH, dissolved oxygen), hydraulic conditions, bottom grain sizes or sedimentation rates. In addition to population and community changes, morphological and geochemical changes can also be detected in the ostracod carapace, which serves as a tracer of the water quality. All these features permit to delimit the spatial effects of urban sewages, mining effluents, agricultural wastes, watershed deforestation or road building. These data are the basis for the palaeoenvironmental reconstruction of cores, with an interesting application to archaeology. In addition, favourable results of recently developed bioassays, coupled with an important variability of local assemblages under changing conditions in both waters and sediments, suggest that these microcrustaceans may included between the most promising sentinels groups in freshwater areas. These microcrustaceans show high sensitivity to pesticides, herbicides, heavy metal pollution and oil inputs.

Mediterranean river systems are characterised by more diverse fish assemblages and regional ecological processes compared with the rest of Europe. A data set from Mediterranean France, Iberia and Greece ( 2000 sites) was used to describe the characteristics of fish assemblages, explore their responses to anthropogenic disturbance and analyse the implications for river quality assessment. There was a southwards decline in species richness per site, but endemicity and proportion of alien species increased. Sites in the eastern Mediterranean had higher endemicity, lower site richness and lower number of alien species than sites in western Mediterranean Europe. Assemblage composition differed between Mediterranean sub-regions, but was dominated by three major fish types: a salmonid fish type common throughout the study area and two cyprinid-dominated fish types (in some sub-regions, Salmo trutta L. is present but not numerically dominant), corresponding to a gradient in hydrological and temperature regimes. Metric responses to perturbation were compared with those found at the European (larger scale) and basin (smaller scale) levels. Overall metric response was weaker in this Mediterranean application. The best responses to human pressure were usually obtained with abundance-based metrics and included the contribution of naturalised alien species. Some widespread alien species contributed to the response to anthropogenic alteration (notably Cyprinus carpio L. and Lepomis gibbosus (L.)). K E Y W O R D S :alien species, fish metrics, fish types, guilds, human impacts, Mediterranean streams.

Abstract1. This study analyses quantitatively the association between habitat characteristics and annual variation in water availability on otter (Lutra lutra L.) distribution in a large Mediterranean area (13717 km 2 ) in southern Spain 2. There was a strong positive correlation between habitat quality, estimated after the two first components of a Principal Component Analysis of a matrix habitat variables x sites, and an index of otter presence/absence, otter presence being most probable in unpolluted and undisturbed sites and surrounded by woodland.3. After univariate analysis, the main freshwater habitat features were statistically different between sites with presence of otters and sites lacking them. In general, otters occurred in medium-sized fluvial habitats, with high bankside vegetation cover, unpolluted, with low or very low human disturbance and surrounded by forests or dehesas (Mediterranean-like savannah).4. Water availability, inferred from the water balance, strongly influenced otter distribution and the type of water body mostly used. As water availability increased so did the otter distribution range and during these periods they tended to colonise low-order streams. During periods of water shortage, otters were most probably found in high-order streams and reservoirs, the only sites that kept water.5. In conclusion, otter distribution in Mediterranean areas is strongly influenced by two factors: 1) man-induced habitat degradation and 2) natural variability in water availability. The addition of the second factor to the first one introduces additional risks to the survival of otter populations in Mediterranean areas compared with more northerly and humid areas, usually only subjected to the first threatening factor.

Patterns of habitat use by fish assemblages in two chalk streams in southern England were examined to identify species preferences with respect to major habitat gradients. Both study sites although differing in some physical habitat characteristics, mainly channel width, water temperature and instream cover, could be similarly arranged along a continuum extending from erosional to depositional habitats. Twelve fish species were collected from stream surveys conducted during July 1993. The habitat was partitioned into six fish species associations that could be assigned to three habitat guilds: depositional (Barbatula barbatula, Gasterosteus aculeatus and Anguilla anguilla), riffle (Leuciscus leuciscus, Thymallus thymallus and Salmo salar) and generalist (Salmo trutta, Phoxinus phoxinus, Gobio gobio, Cottus gobio, Lampetra planeri and Pleuronectes flesus).At low to moderate densities the different species associations were collected in the same habitat patch, but at higher densities there was a clear tendency to mutual avoidance. In particular, large trout appeared as strong interactors that tended to exclude other species from their territories. We hypothesize that the fish assemblage of the Mill Stream and Bere Stream have partitioned the habitat in such a way as to minimize potential competition.