Aim We investigated the biogeographical patterns of phytoplankton, zooplankton and fish in freshwater ecosystems. We tested whether spatial distance or environmental heterogeneity act as potential factors controlling community composition.Location Northern and central Greece, eastern Mediterranean.Method Data on 310 phytoplankton, 72 zooplankton and 37 fish species were collected from seven freshwater systems. Species occurrence data were used to generate similarity matrices describing community composition. We performed Mantel tests to compare spatial patterns in community composition of phytoplankton, zooplankton and fish. Next, we examined the correlation between geographical distance and the degree of similarity in community composition. The analysis was repeated for different taxonomic, trophic and sizebased groups of the microorganisms studied. We assessed different environmental variables (topographic and limnological) as predictors of community composition.Results Phytoplankton community composition showed a strong positive correlation with environmental heterogeneity but was not correlated with the geographical distance between systems. Zooplankton community composition was unrelated to geographical distance and was only weakly correlated with environmental variables. In contrast, fish community similarity decayed significantly with distance. We found no relationship along all pairwise comparisons of the compositional matrices of the three groups. The pairwise comparisons of the different taxonomic, trophic and size-based groups of the microorganism communities studied were in accordance with the results for the entire microorganism community. Main conclusionsOur results support the proposition that the biogeography of microorganisms does not demonstrate a distance-decay pattern and further suggest that, in reality, the drivers of distribution depend on the specific community examined. In contrast, the biogeography of macroorganisms was affected by geographical distance. These differences reflect the dispersal abilities of the different organisms. The microorganisms exhibit passive dispersal through the air, with local environmental conditions structuring their community composition. On the other hand, for macroorganisms such as fish, the terrestrial environment could pose barriers to their dispersal; with fish structuring distinctive communities over greater distances. Overall, we suggest that the biogeography of freshwater phytoplankton and zooplankton reflects

We examined the relative contribution of environmental heterogeneity and dispersal limitation on freshwater fish community composition in 18 Greek protected lakes and reservoirs. Environmental heterogeneity was measured by spatial pattern metrics (calculated by digital map processing, e.g., patch richness density, area-weighted mean patch area), altitude, maximum lake depth and trophic status. Dispersal limitation was measured by straight-line distances among lake centres. Ecosystems were clustered according to species composition. We examined the correlation of similarity in species composition among ecosystems with that of environmental heterogeneity and with straight-line distances, for the entire dataset, as well as for the occurring clusters. Fish species richness increased with ecosystem area and decreased with altitude. The clusters identified (aquatic ecosystems of Northern vs. ecosystems of Western Greece), implied an underlying biogeographical pattern as defined, with Pindus range acting as a natural barrier. Between ecosystems similarity, based on fish species composition, showed a weak to insignificant correlation with environmental heterogeneity, but was significantly correlated to dispersal limitation for the entire dataset as well as within each occurring cluster. Thus, natural barriers, species biogeography and dispersal limitation played a more significant role in shaping freshwater fish communities than environmental heterogeneity.

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Materials and methods:The present study is the first to apply DNA barcoding on identifying 37 freshwater fish species from the rich Balkan ichthyofauna. Results: The results are highly successful since in most cases barcodes cluster according to species, in agreement with morphological taxonomic studies. This is also evident based on mean conspecific and congeneric Kimura two-parameter distance values. The 5.6-fold difference between these values is lower than previous barcoding studies, possibly due to the restricted samplings and the recent taxonomy reevaluation for several species. A number of species were identified, where future work is needed: For the species Scardinius erythrophthalmus, Perca fluviatilis, and Rutilus rutilus, the divergence values found among conspecific populations could warrant their placement into different species; for Barbus and Rhodeus populations, the reported interspecific distances found were lower than expected; and for Cobitis species, the application of barcoding seems problematic, due to their complicated reproduction. Conclusion: The extension of this work to other Greek or even Balkan freshwater systems should clarify the situation.

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In the present work, we review the current state of knowledge and research trends on freshwater fishes of Greece to assess a) the status of fish populations and their habitats; b) the state and priorities of fisheries science and legislation; c) priority gaps and needs in freshwater fish habitat management; and d) future strategies for freshwater fishes and aquatic resources. Freshwater fish fauna of Greece currently consists of 135 taxa including diadromous and introduced species. The taxonomy of some taxa is unclear. The distribution and origin of freshwater fishes, especially endemics, has been attributed mainly to the geological history of the country. Commercial fishing in inland waters is conducted mainly in 32 natural or artificial water systems. The total annual commercial catch for the 1988–2000 period ranged from 1,950 t in 1988 to 1,810 t in 2000 with a mean annual catch of about 1,500 t. The major part of inland catches comes from lakes, while catches from rivers are of minor importance. Aquaculture contributes greatly to the total production of freshwater fishes. The total annual aquaculture production for the period 1988–2000 ranged from 2,638 t to 3,656 t with a mean annual production of 2,832 t, 1.33 to 2.02 times higher than the traditional inland catches. Due to human activities, Greece has lost 75% of its wetland area since 1900. Today, the pressures upon the surface freshwater resources are moderate with the exception of some systems where human intervention is intense, leading to species extirpations from their type localities. Recently, surface waters have been classified under the auspices of the European Union Water Framework Directive where fishes have an essential role as indicators of the ecological integrity of running waters. Under this concept, there is an increasing emphasis on gathering biological data, to serve a broad-spectrum of environmental objects and plans such as the protection of endangered and threatened species. However, to date effective management and conservation of freshwater fishes and fisheries have not been much considered in the management of freshwaters of Greece. Existing plans for managing aquatic inland resources primarily focus on water usage and do not include specific, enforceable monitoring and management objectives, conservation actions, and control measures for aquatic habitats and fish communities, including endangered and threatened fishes. It is concluded that future efforts need to be directed to severely endangered or nearly extinct species. Furthermore, the creation of GIS-based databases for incorporating all the information on species, habitats and genetic diversity should be addressed under the guiding principle of conserving aquatic biodiversity.

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