Leonidas Vardakas

Leonidas Vardakas
Hellenic Centre for Marine Research | hcmr · Institute of Marine Biological Resources and Inland Waters

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96
Publications
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Publications

Publications (96)
Article
Non-perennial rivers and streams (NPRS) cover > 50% of the global river network. They are particularly predominant in Mediterranean Europe as a result of dry climate conditions, climate change and land use development. Historically, both scientists and policy makers underestimated the importance of NRPS for nature and humans alike, mainly because t...
Article
1. Identifying key factors in species' habitat requirements can be of use in defining critical habitats for their conservation, as well as in assisting the prioritization of habitat restoration actions. So far, most studies on habitat use by freshwater fishes have been focused on widespread and economically important species (e.g. salmonids). 2. Th...
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Fish introductions, particularly in areas of high biological diversity and endemism, represent a major threat for biodiversity. In the Balkan Peninsula, 60 fish species have been introduced to date, of which 36 have become naturalised in inland waters. Since the Balkans are one of the world’s 35 biodiversity hotspots, this large presence of alien f...
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1. Rainbow trout is ranked as one of the world's worst alien invasive species; in Europe however the extent of established populations remains localized and poorly reported. This study aims to assess rainbow trout establishment in Greece and explores the factors of establishment success or failure. 2. We analyzed fish samples and site specific env...
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This study provides an annotated checklist of the freshwater fish species recorded in lentic ecosystems of Greece. Species distributional data were derived from an extensive review of published and unpublished sources and were evaluated for their consistency, adequacy and reliability. Overall, 650 freshwater lentic ecosystems (149 natural and 501 a...
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Even though the ecological impacts of invasive alien species (IAS) have been well studied, social aspects of IAS in freshwater ecosystems are still poorly explored. This study aimed to assess the perceptions associated with non-indigenous freshwater fish species (NIFS) among environmental-related professional and non-professional stakeholders in a...
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A few studies have used historical inland fisheries data for defining reference points necessary for fisheries management. We developed a historical baseline of catches for inland fisheries of Greece during 1928–2019, with the interwar period (1928–1939), a period of intense political and socio-economic turmoil, serving as a pre-development referen...
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Electronic decision-support tools are becoming an essential component of government strategies to tackle non-native species invasions. This study describes the development and application of a multilingual electronic decision-support tool for screening terrestrial animals under current and future climate conditions: the Terrestrial Animal Species I...
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Human-induced biological introductions pose a major threat to global biodiversity, and this is especially frequent in the eastern Mediterranean region, which is a globally important biodiversity hotspot area of high conservation value. To predict at which level introduced species in this region might become invasive under current and projected clim...
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Non-indigenous fish species (NIFS) can cause severe ecological impacts on the invaded ecosystems and are considered as one of the leading factors of freshwater biodiversity loss. Unraveling the spatial overlap between NIFS and critically endangered (CR) fish species can contribute to targeted conservation actions to minimize the potential negative...
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The threat posed by invasive non-native species worldwide requires a global approach to identify which introduced species are likely to pose an elevated risk of impact to native species and ecosystems. To inform policy, stakeholders and management decisions on global threats to aquatic ecosystems, 195 assessors representing 120 risk assessment area...
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Many studies around the globe have documented that the introduction of non-indigenous fish species (NIFS) may pose severe impacts on native biota, ecosystem functioning and ecosystem services. In Greece, publications on NIFS have increased in recent decades, however review studies of past and current scientific research on freshwater NIFS in the co...
Conference Paper
Full-text available
The introduction of non-indigenous fish species (NIFS) to freshwater ecosystems is considered as one of the leading factors associated with freshwater biodiversity loss. Unravelling the spatial overlap between NIFS and critically endangered (CR) fish species can contribute to targeted conservation planning and actions to minimize the potential nega...
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The freshwater ichthyofauna of Greece is characterized by high diversity and endemism and faces various conservation challenges. Despite significant efforts, mainly with traditional assessment methods, the precise taxonomic status and geographic range of some of the currently acknowledged fish species remain insufficiently explored. Here, the resul...
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The design and implementation of appropriate management actions to tackle the spread and negative impacts of non-indigenous fish species (NIFS) in freshwater ecosystems still remains a complex task. In an effort to address the limitations of current managerial approaches, our study develops and applies a classification framework to define non-indig...
Article
Environmental changes due to non-native species introductions and translocations are a global concern. Whilst understanding the causes of bioinvasions is important, there is need for decision-support tools that facilitate effective communication of the potential risks of invasive non-native species to stakeholders. Decision-support tools have been...
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Full-text available
Environmental changes due to non-native species introductions and translocations are a global concern. Whilst understanding the causes of bioinvasions is important, there is need for decision-support tools that facilitate effective communication of the potential risks of invasive non-native species to stakeholders. Decision-support tools have been...
Article
While in recent years intermittent rivers and ephemeral streams (IRES) are receiving increasing attention from ecologists, fish metacommunity dynamics have drawn less attention than other taxa. In this study, we explored fish metacommunity dynamics at a Mediterranean intermittent river (Evrotas River, Southern Greece) to unravel which factors (i.e....
Article
Although in‐channel and floodplain large wood (LW) has been recognized as an important component of lotic ecosystems, there is still limited knowledge on the recruitment, mobility and retention of LW in rivers with an intermittent hydrological regime. In this study, we analysed the LW characteristics and related reach‐scale variables of 22 reaches...
Article
Interspecies and intraspecies variation in the use of wooded habitats has been studied for salmonids, but little is known about nonsalmonid species. In this study, we explored spatiotemporal differences in the distribution of three cyprinid species at habitats of varying wood density and at habitats of varying heterogeneity in a Mediterranean inter...
Article
River restoration with the use of in-stream structures has been widely implemented to maintain/improve physical habitats. However, the response of aquatic biota has often been too weak to justify the high costs of restoration projects. The ecological effectiveness of river restoration has thus been much debated over claims that large-scale environm...
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The rapid decline of the Greek native Valencia letourneuxi, and its recently described sister species Valencia robertae, has been often attributed to habitat degradation, as well as aggression from or resource competition with the alien mosquitofish Gambusia holbrooki. The mosquitofish is extremely wide-spread in Mediterranean freshwater ecosystems...
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The freshwater Fish Invasiveness Screening Kit (FISK) has been applied in 35 risk assessment areas in 45 countries across the six inhabited continents (11 applications using FISK v1; 25 using FISK v2). The present study aimed: to assess the breadth of FISK applications and the confidence (certainty) levels associated with the decision-support tool’...
Article
Olive mill wastewaters (OMW) discharging in river ecosystems cause significant adverse effects on their water chemistry and biological communities. We here examined the effects of OMW loads in four streams of a Mediterranean basin characterized by changing flow. The diatom and macroinvertebrate community structures were compared between upstream (c...
Article
Olive oil production generates large volumes of wastewaters mostly in peri-Mediterranean countries with adverse impacts on the biota of the receiving aquatic systems. Few studies have however documented its toxicity on aquatic species, with an almost total lack of relative studies on fish. We assessed the acute and sub-chronic OMW toxicity, as well...
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The extreme seasonal environmental variation of intermittent rivers has a profound effect on freshwater fish communities. Yet, few studies have examined the consequences of the seasonal cycles of flooding and drying to fish condition and reproduction in these ecosystems. In this study, we compared the body condition, reproduction and diet of two ch...
Article
Mediterranean lotic waters such as rivers, streams and springs are poorly monitored for non-indigenous fish species (NIFS). Since these systems are stressed by multiple anthropogenic pressures, it is important to build robust procedures to track NIFS distribution and spread. This study applies a multi-faceted assessment of NIFS in the lotic ecosyst...
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Environmental flow assessments (EFAs) are widely researched and applied worldwide. However, model-based frameworks integrating the flow requirements of multiple ecosystem components have been primarily developed for perennial watercourses, being inherently inapplicable in intermittent rivers (IR), which are common worldwide and may dominate arid, s...
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Studies targeting to explore fish species diversity and seasonal surface variations at small-sized, lentic ecosystems are extremely limited in the Mediterranean region. These ecosystems are often ignored by scientists under the erroneous assumption that they play an insignificant socio-economical role or they are of low ecological importance. This...
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The hydrological and biological complexity of temporary rivers as well as their importance in providing goods and services is increasingly recognized, as much as it is the vulnerability of the biotic communities in view of climate change and increased anthropogenic pressures. However, the effects of flow intermittency (resulting from both seasonal...
Article
Although large wood (LW) has been intensively studied in forested basins of humid temperate climates, data on LW patterns in different fluvial environments are rather scarce. Therefore, we investigated the dimensions, characteristics, longitudinal distribution, and dynamics of LW along a 4.05-km-long reach of an ephemeral channel typical of Europea...
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This review presents the main results of a 10-year research study conducted in a Mediterranean intermittent basin (Evrotas River). By assembling the main outcomes of past and ongoing research projects, this study provides an overview of multiple stressor effects, with emphasis on water scarcity , focusing on hydro-biogeochemical processes, as well...
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Predicting alien species' establishment through climate matching may inform management actions preventing future invasions. The aim of the current study was to evaluate the climate match of the sailfin molly (Poecilia latipinna) worldwide, with emphasis on Europe and the Mediterranean. A literature review indicated that the species presents a total...
Article
Water stress is a key stressor in Mediterranean intermittent rivers exacerbating the negative effects of other stressors, such as pollutants, with multiple effects on different river biota. The current study aimed to determine the response of macroinvertebrate and fish assemblages to instream habitat and water chemistry, at the microhabitat scale a...
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River ecosystems are subject to multiple stressors that affect their structure and functioning. Ecosystem structure refers to characteristics such as channel form, water quality or the composition of biological communities, whereas ecosystem functioning refers to processes such as metabolism, organic matter decomposition or secondary production. St...
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The ornamental aquarium trade has been responsible for several introductions of non-indigenous species in freshwater ecosystems. This report confirms the presence of an established non-native molly population in a tectonic, brackish, geothermal lagoon located in Greece (Lake Vouliagmeni near Athens). The Vouliagmeni molly was positively identified...
Article
Temporary rivers are dynamic and complex ecosystems that are widespread in arid and semi-arid regions, such as the Mediterranean. Biotic communities adapted in their intermittent nature could withstand recurrent drought events. However, anthropogenic disturbances in the form of water stress and chemical pollution challenge biota with unpredictable...
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Desiccation and rewetting are the driving forces in intermittent streams that affect fish community attributes. A one-year field study was conducted at an intermittent reach of a Mediterranean river (Evrotas River, S. Greece) to assess the variation in fish community attributes (density, abundance, size structure and mortality of three endemic cypr...
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Full-text available
Invasive alien species (IAS) are a significant and growing problem worldwide. In Europe, some aspects of IAS have been addressed through existing legal instruments, but these are far from sufficient to tackle the problem in a comprehensive manner. The Top 20 IAS issues for Europe were determined at the 1st Freshwater Invasives - Networking for Stra...
Chapter
This chapter is the outcome of a 10-year ecological monitoring survey in the Evrotas River Basin (ERB). Synthesising the main outcomes of past and ongoing research projects, it presents an overview of the basin’s geographical, geological, hydrological and ecological features, focused on the ecological status according to the Water Framework Directi...
Conference Paper
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Presentation of pertinent results and interpretations from a state-wide review of the conservation status of fishes (primarily freshwater species) which are of European conservation interest based on the Habitats Directive (92/43/EE).
Conference Paper
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During this study, the seasonal variations of the surfaces in a complex of nine small freshwater ecosystems in NW Greece were investigated from March 2013 to March 2014. Additionally, electrofishing was conducted in all lakes οn two occasions (March and July 2013), in order to provide a fish faunistic list. Overall, water surface variations in all...
Conference Paper
Full-text available
A nationwide ichthyological survey designed to meet the demands of the Water Framework Directive 2000/60/EC for the ecological status assessment in lotic systems was conducted between summer 2012 and autumn 2015. A total of 127 river basins were surveyed and 1,096 fish samplings were conducted in 449 sites using electrofishing devices. Overall, 237...
Conference Paper
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We used 1.208 fish samples collected primarily through electrofishing from 93 hydrological basins in six freshwater ecoregions of Greece to show that freshwater fishes exhibit positive relationships between local abundance and geographic distribution. Possible ecological mechanisms accounting for the pattern and we explore its practical implication...
Article
Full-text available
A wide-ranging river fish survey was executed in the summer of 2009 as part of the preparatory actions for the establishment of a monitoring programme for the EU Water Framework Directive (WFD). This was the first extensive electrofishing campaign for WFD standardised bioassessment in Greece and the experience and insights gained are used here to p...
Article
Full-text available
The invasion of non-indigenous freshwater fish species is one of the most important threats to aquatic biodiversity. Similar to other Mediterranean countries, Greece is considered a hot spot for freshwater biodiversity, with many range-restricted endemics of high conservation concern. The aim of the present study was to undertake a risk screening a...
Article
The invasion of non-indigenous freshwater fish species is one of the most important threats to aquatic biodiversity. Similar to other Mediterranean countries, Greece is considered a hot spot for freshwater biodiversity, with many range-restricted endemics of high conservation concern. The aim of this study was to undertake a risk screening assessme...
Technical Report
On-site monitoring of the inland and coastal zone waters ecological status at water basin level and creation of a relevant database. https://cloudfs.hcmr.gr/index.php/s/ZcCqK4sv8XKJ9kP#pdfviewer
Research
The distribution patterns of fish assemblages within streams can provide insights for river type classifications and may warrant specific conservation actions. However, there is limited knowledge of how fish assemblages assort along a longitudinal axis in Mediterranean intermittent streams. Patterns in spatial and temporal distribution of fish comm...
Conference Paper
Full-text available
This poster present's HCMR's rapid assessment method for inland waters fish sampling. This method, used since 2003 provides a consistent description of the assemblage of fishes (i.e. percentage composition, relative abundance and size-class structure) and habitat parameters. The three-page field form of the protocol also has an operations manual (I...
Conference Paper
Full-text available
Microhabitat use by three Hellenic endemic cyprinids was studied at the Evrotas River (Southern Greece). Data were obtained by electrofishing at a reference reach and at a reach impacted mainly by pollution. Species’ comparisons indicated differences in habitat use, with Squalius keadicus being associated with higher flows at the impacted reach, wh...
Conference Paper
Full-text available
Microhabitat use by two Greek endemic cyprinids was studied at two relatively undisturbed sites in Evrotas and Evinos River, by electrofishing and snorkelling respectively. The primary goal of this study was to test, for the first time for Greece, the applicability of these two methods in the study of habitat use and habitat availability for two Gr...
Book
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Freshwater Fishes and Lampreys of Greece: An annotated checklist is the 8th volume of Monographs on Marine Sciences published by the Hellenic Centre for Marine Research (HCMR), Athens, Greece. This work provides a list of all species of fishes occuring in inland freshwaters; the most recent, carefully referenced account of its kind. The work is par...