α- and β-Diversity Patterns of Macrophytes and Freshwater Fishes are Driven by Different Factors and Processes in Lakes of the Unexplored Southern Balkan Biodiversity Hotspot

Beyond taxonomic diversity patterns - investigating how α and β components of macrophyte functional diversity respond to environmental gradients in lotic ecosystems of Greece

In addition to quantifying the taxonomic diversity of aquatic communities, understanding the patterns of alpha functional diversity (α-diversity) and exploring changes in functional dissimilarity (β-diversity) can improve our understanding on how ecosystems respond to environmental changes. In this study, we quantified functional alpha (α) and beta (β) diversity of macrophytic assemblages from river sites in Greece and then, examined relationships with water quality parameters and hydromorphological factors. We assigned 6 traits (Ellenberg nutrients indicator, Ellenberg light indicator, growth form, leaf size, leaf type, fruit size) to a total of 36 hydrophyte species and calculated three indices of functional diversity (functional richness, functional dispersion and functional evenness). We also estimated the total β-functional diversity and its' main components, turnover and nestedness. To assess the effects of water quality (including physical and chemical variables) we used Generalized Additive Models (GAM) for alpha functional diversity indices and Generalized Dissimilarity Models (GDM) for beta functional diversity. We performed Kruskal-Wallis tests and permutational multivariate analysis of variance (PERMANOVA) to search for significant variations of α- and β-diversity among the hydromorphological factors. Our results showed that macrophyte growth form and light preference were important trait characteristics that explained a large share of the total variance of functional composition. We also found relatively low taxonomic and functional richness, whereas taxonomic and functional dissimilarity were mostly attributed to species turnover, which expresses the changes in taxonomic and functional composition. We found significant relationships between functional dispersion and functional evenness with pH and oxygen saturation, whereas functional dissimilarity was driven only by geographic distance, although the GDM explained a small portion of the total variance. Functional richness, dispersion and evenness were significantly higher at systems with fine substrates and deep waters with low or high flow compared to systems with coarser substrates and riffle habitats. We also found significant variation in functional dissimilarity among the hydromorphological factors, although much of the total variance remained unexplained. Overall, our study highlights the importance of considering the functional diversity of aquatic plant assemblages within the frame of freshwater monitoring and conservation plans.

Linkages between pelagic and benthic biota in a deteriorated coastal lake after restoration, Maruit, Egypt

Until the 1960s, Lake Maruit was one of Egypt's most productive coastal brackish lakes. Continuous polluted discharge from Alexandria city resulted in long-term deterioration. The Egyptian government started a lake restoration program in 2010. Biological linkages between pelagic and benthic communities were assessed in November 2012 using parasitism and predation. This study examined ectoparasites infesting tilapia fish from 300 samples. The platyhelminth ectoparasite, Monogenea, and parasitic-copepod Ergasilus lizae were detected. Platyhelminthes parasitized Oreochromis niloticus and Oreochromis aureus, whereas the crustacean parasitized Coptodon zillii. The parasitic prevalence was low for Cichlidogyrus sp. and Ergasilus lizae. Benthic biotas were similar across basins. Fish abundance does not respond directly to benthic biotic components. Phytoplankton and benthic microalgae were not the main fish diet. Data on Halacaridae and fish clustered, indicating that either Halacaridae responds to their environment like fish or fish prey upon them because of their size. Linear correlations between pelagic, benthic biota, and parasite-infected fish indicate parasites may control their hosts. Some bioindicators indicate that stressed ecosystems differ from unstressed ecosystems. Fish species and biota abundances were low. Inconsistency in the food web and an absence of direct interactions between prey and predators are bioindicators of disturbed ecosystems. The low prevalence of ectoparasites and lack of heterogenous distribution of the various examined biota are bioindicators of habitat rehabilitation. Ongoing biomonitoring to better understand habitat rehabilitation is suggested.

Trophic Patterns of Freshwater Fish across the Balkan Biodiversity Hotspot

Ecological information regarding trophic patterns and the inherent structure of freshwater aquatic communities is considered fundamental in ecological research. In this study, the trophic patterns of the Greek freshwater fish fauna, belonging to the Balkan biodiversity hotspot, were investigated, and comparisons of freshwater fish species feeding habits among the Greek freshwater ecoregions were performed. The analyses based on the widely used trophic level index and the available composition feeding datasets, along with the utilization of clustering methods, indicated seven major distinct trophic guilds in the Greek ecoregions. The trophic level of the studied fish species ranged from 2.0 to 4.5, thus being within the expected values for freshwater ecosystems, revealing the presence of both top predators and primary consumers. The highest trophic level values were found in the ecoregions of northern Greece. The results also exhibited considerable predominance of higher-trophic-level zooplanktivorous and insectivorous freshwater fish species in the mainland, compared to lower-trophic-level opportunist species in the island-isolated ecoregions. These results could be used for the application of ecosystem-based models and the formulation of conservation and fishery management schemes.

Responses of different facets of aquatic plant diversity along environmental gradients in Mediterranean streams: Results from rivers of Greece

Aquatic and riparian plants play a crucial role in the functioning of riverine ecosystems. Hence, analyzing multiple facets of plant diversity could be extremely useful for assessing the ecological integrity of lotic ecosystems. The main objective of this study was to investigate the response of multiple facets of aquatic plant diversity, such as species richness, taxonomic distinctness and compositional dissimilarity, to environmental factors (i.e. nutrient pollution and hydromorphological alteration) in 72 stream reaches of mainland Greece. We employed Generalized Additive Models to identify the variables with the highest influence and examine the response of species richness and taxonomic distinctness to environmental gradients. The relationship between compositional dissimilarity and the environment was examined with Generalized Dissimilarity Modelling. Our results supported our hypothesis that human disturbances play a considerable role in shaping macrophyte assemblages. In particular, phosphates and hydromorphological modification were significant predictors of species richness, whereas taxonomic distinctness was unaffected by indicators of anthropogenic stress but it was influenced mostly by elevation, water temperature and pH. Concerning the compositional dissimilarity, geographic distance, elevation, temperature and total inorganic nitrogen were the most important environmental parameters. Our findings suggest that human stressors, such as hydromorphological modification and nutrient enrichment, affect the plant species richness at stream reach scale, but when considering community composition or taxonomic distinctness, environmental factors associated with the natural variability (e.g. elevation, temperature and geographic distance) are of higher importance. Overall, our results emphasize the advantage of examining multiple aspects of diversity when designing conservation schemes and management plans for riparian areas.

Four Decades of Surface Temperature, Precipitation, and Wind Speed Trends over Lakes of Greece

Climate change is known to affect world’s lakes in many ways. Lake warming is perhaps the most prominent impact of climate change but there is evidence that changes of precipitation and wind speed over the surface of the lakes may also have a significant effect on key limnological processes. With this study we explored the interannual trends of surface temperature, precipitation, and wind speed over 18 lakes of Greece using ERA5-Land data spanning over a period of almost four decades. We used generalized additive models (GAMs) to conduct time-series analysis in order to identify significant trends of change. Our results showed that surface temperature has significantly increased in all lakes with an average rate of change for annual temperature of 0.43 °C decade−1. With regard to precipitation, we identified significant trends for most lakes and particularly we found that precipitation decreased during the first two decades (1981–2000), but since 2000 it increased notably. Finally, wind speed did not show any significant change over the examined period with the exception for one lake. In summary, our work highlights the major climatic changes that have occurred in several freshwater bodies of Greece. Thus, it improves our understanding on how climate change may have impacted the ecology of these important ecosystems and may aid us to identify systems that are more vulnerable to future changes.