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Article

The Compositional and Functional Diversity of a Mediterranean Urban Lake’s Fish Fauna over the Past 120 Years

by
Olga Petriki
* and
Dimitra C. Bobori
Laboratory of Ichthyology, Department of Zoology, School of Biology, Aristotle University of Thessaloniki, Box 134, GR54124 Thessaloniki, Greece
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(14), 6099; https://doi.org/10.3390/app14146099
Submission received: 11 June 2024 / Revised: 7 July 2024 / Accepted: 9 July 2024 / Published: 12 July 2024
(This article belongs to the Special Issue Monitoring and Conservation of Freshwater Biodiversity)
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Abstract

This study examines the compositional (taxonomic) and functional diversity changes in the fish fauna of a Mediterranean urban lake (Lake Kastoria) over a period of 12 decades (1900–2020, as of 2022). Moreover, the current status (2010 and 2022) of the fish fauna is assessed along with the lake’s ecological quality. Intentional or accidental species introductions resulted in significant compositional changes in the lake’s fish fauna. The functional richness among the assemblages from 1900 and 2020 was increased due to species introductions, resulting in a peak of functional dissimilarity in 1990, when most introductions took place. However, the functional dissimilarity measures revealed that there have been moderate changes in groups of the functional traits which may be indicative of high species competition. The lake’s open waters are dominated by Rutilus rutilus and the introduced species Perca fluviatilis and Lepomis gibbosus. The estimated ecological quality was higher in 2022 than in 2010, categorizing the lake as having “Moderate” quality and providing an upgrade from its earlier ‘Poor” condition. This positive shift is attributed in part to the burgeoning population of Perca fluviatilis, as evidenced by increased catch rates. The species’ resurgence may be linked to enhancements in the lake’s physicochemical parameters, potentially facilitated by more effective treatment of urban wastes. The study underscores the complex interplay between species introductions, functional diversity, and ecological quality in the urban Lake Kastoria, highlighting the need for continued monitoring and management efforts to sustainably preserve and enhance the biodiversity and ecological integrity of urban aquatic ecosystems.

Graphical Abstract

1. Introduction

Urbanization and ecological changes are intertwined global phenomena that significantly influence biodiversity and ecosystem services [1,2]. As the world’s population continues to grow, urban areas are expanding at unprecedented rates [3]. This rapid urbanization has profound implications for natural habitats, including freshwater ecosystems such as lakes and rivers [4]. Urbanization often leads to the degradation of freshwater ecosystems through pollution, altered hydrology, and the introduction of invasive species. These changes can have severe consequences for the biodiversity and ecological integrity of urban lakes and rivers [5]. Among others, the introduction of fish species and habitat degradation have extensive and interconnected impacts on lake ecosystems, affecting ecological, environmental, and socio-economic aspects [6]. Introduced species can compete with native ones for resources, often leading to native species’ decline or extinction, especially if the newcomers are more aggressive or adaptable [7,8]. Non-native predators can significantly reduce native species’ populations of many taxonomical groups [6], while hybridization with closely related non-natives can dilute native genetic integrity [9,10]. Habitat degradation also impacts fish fauna in multiple ways [11,12]. Nutrient runoff can cause algal blooms, leading to oxygen depletion and fish deaths. Erosion from land use can smother fish eggs and alter habitats, while pollution introduces toxins harmful to aquatic life and humans. Construction activities change the water flow and temperature, making environments less hospitable for native species. These changes impact commercial and recreational fisheries, potentially harming local economies.
Urban lakes serve as vital ecosystems within densely populated areas, offering recreational opportunities and supporting biodiversity [13,14]. The Mediterranean region, characterized by its unique climate and biodiversity, is particularly vulnerable to the impacts of urbanization [15]. Mediterranean ecosystems are global biodiversity hotspots, home to a diverse array of species, many of which are endemic [16]. However, the region also faces intense pressures from human activities, including urban expansion [17].
One example of an urban lake located in the eastern Mediterranean region is Lake Kastoria, situated in the heart of a bustling town in Greece. The history of the lake is deeply intertwined with both natural processes and human activities, shaping the ecosystem over millennia. Today’s lake is a remnant of a much larger ancient lake (with an estimated maximum depth of over 50 m during the Quaternary period). Remarkably, evidence of the lake’s importance to humans dates to ancient times, as exemplified by the presence of the Dispilio archaeological site, which dates back to the Neolithic period around 5600 BC [18]. In the site, prehistoric fishing gears were discovered, offering invaluable insights into prehistoric human life and underscoring the longstanding relationship between humans and the lake’s resources.
Over the years, the fish fauna of Lake Kastoria has undergone significant changes, influenced by both natural processes and human activities. Specifically, one of the most notable anthropogenic actions impacting the lake’s fish fauna has been the introduction of non-native fish species for biomanipulation reasons, fisheries enhancement, or accidentally [19]. Additionally, habitat degradation and pollution resulting from urbanization, agricultural runoff, and industrial activities have further impacted the fish fauna of Lake Kastoria. Overfishing has also played a significant role in the decline in fish populations in the lake [20].
In the present work, we delve into the history of the lake’s fish fauna, examining the anthropogenic impacts that have shaped its biodiversity, and try to quantify changes in species composition and functional diversity. Additionally, we assess the current status of the fish fauna according to the requirements of European Water Directive 2000/60/EC (WFD). Since data spanning 120 years are rare and valuable, providing insights into the historical ecological changes and long-term trends, our research, within the broader context of global ecological and urbanization trends, aims to highlight the relevance of this local case study for global biodiversity conservation efforts.

2. Material and Methods

2.1. Study Area

2.1.1. Position and Morphological Characteristics

Lake Kastoria (Figure 1) is located at an altitude of 629.5 m.a.s.l. It is a shallow karstic lake with an average surface area of 27.9 km2, an average depth of 4.4 m, and a maximum depth of 9.1 m. It has an elliptical shape with two natural recesses and features the Koritsa Peninsula, where the town of Kastoria is located. According to the latest census, the population of the regional unit amounts to 45,929 inhabitants [21], with approximately 33,095 residents in the wider city area and an estimated population density in the drainage basin of about 170 inhabitants/km2. Notably, the town’s population has changed over the years, from 10.049 inhabitants in 1951 to 16.958 inhabitants in 2011 [22], and reaching 20,636 inhabitants in 2021 [21].
The drainage basin is closed, covering an area of 263.6 km2, with an average altitude of 895 m. The climate of the region is characterized as Mediterranean–Continental with particularly cold winters [23,24]. It is humid with mesothermal conditions, featuring a mean annual precipitation of around 700 mm [25] and a mean temperature of around 13 °C. The range of mean maximum temperatures spans from 6 °C to 28.4 °C, while the range of mean minimum temperatures varies from 1 °C to 15.9 °C [23,24]. The rainy season lasts from September to May, while the dry period is from June to August [24,25].

2.1.2. Hydromorphological and Limnological Characteristics

Kastoria became a hypereutrophic lake as eutrophication increased over the past decades [26,27,28]. Approximately 24% of the drainage basin is covered by cultivated land, resulting in large amounts of fertilizers and pesticides reaching the lake [24]. The lake receives surface runoff, surface and underground inflows, and water from uplake springs. Specifically, it receives inflows from 9 streams and outflows towards the Aliakmonas River, but its hydrological balance is negative. Significant amounts of suspended solids are also transported to the lake from its drainage basin and the inflowing streams, posing one of the major threats to the lake [24]. In addition, urban untreated wastewater effluents were directly discharged into the lake until 1994, when the operation of biological treatment commenced [27,29]. However, there is a lack of information on revetment works and ecotone changes which could significantly affect the hydrology and ecological dynamics of the lake. Consequently, the sediment of the lake is rich in organic matter and phosphorus compounds, which, combined with high temperatures in summer and the shallow depth of the lake, favor the release of additional phosphorus quantities, increasing their concentrations in the water.
The lake freezes in the winter for a few days, while thermal stratification occurs in the summer (the thermocline is at 3–4.5 m) when anoxic conditions are often observed at the lake’s bottom [24,30].
After sewage diversion, changes in the lake’s biological communities likely indicated ecosystem recovery [29,31]. However, the improvement in water quality remains insufficient [28,29]. Cyanobacteria dominate the phytoplankton community throughout the year [27,32], while the chlorophyll concentration steadily increases from early summer and reaches its maximum value in September [33]. Notably, during the period 2012–2021, the mean annual total phytoplankton biovolume ranged from 7.3 mm3/L to 83.8 mm3/L [31]. According to [34], some isolated high values of NH4-N, NO3-N, and PO4-P were recorded during a monitoring survey conducted from 2005 to 2006. These elevated levels could be attributed to extreme rainfall and soil flushing, productive activities (such as domestic, agricultural, and recreational activities), or biological processes. Moreover, BOD and COD values have been decreasing as the years progressed from 2014 to 2019 [35].

2.2. Fisheries

The lake’s fisheries have undergone significant changes over time. The exploitation level varies among species, with Cyprinus carpio and Anguilla anguilla (before its extinction) being highly exploited, while nowadays Perca fluviatilis and Carassius gibelio also exhibit commercial importance. Once renowned as one of the country’s most productive fisheries, the lake’s production has seen fluctuations since the 1960s. Peak production was recorded in 1964 at 500 tons, followed by a decline to a minimum of 83 tons in 1976. Subsequently, production increased to 419 tons in 1981, with an average production of 256.6 tons and a yield of 80.2 kg per hectare from 1960 to 1982 [36]. However, according to the local Fisheries Office, there is a further decline in production, with Carassius gibelio being the most commonly caught species.
Limited data on fish populations in the lake hinder comprehensive understanding, but declining populations were attributed to reduced spawning grounds [24] and overfishing. The shallow lake depth and illegal fishing during spawning exacerbate the issue. Additionally, sporadic cases of mass carp killing were linked to environmental factors like increased shoreline vegetation, leading to anoxic conditions, and elevated pH levels.

2.3. Data Acquisition

A literature review was undertaken to elucidate the shifts in the fish species composition over the past several decades, spanning from 1900 to 2020. We consulted several major databases, including Web of Science, Scopus, and Google Scholar, and also searched grey literature sources. The search keywords used included combinations such as “Lake Kastoria and fish fauna”, “historical ecological changes”, “fish species”, and “fisheries”. This resulted in a small number of sources (i.e., 15) from both the scientific and grey literature (in English or Greek) from which data were derived or used for cross-checking. In addition, the functional traits, reflecting the ecological niche for each species, were gathered. These mainly resulted from Fishbase (www.fishbase.org [37]) and included the maximum total length (mm), maximum weight (g), maximum age, length at maturity (mm), trophic level, parental care (defined as the total contribution of parents’ care to their offspring, categorized as none or provided), and generation time. Species preference for the littoral zone (based on the experience acquired through research samplings) was also considered. For Squalius vardarensis, for which the traits’ information was limited, assessments were made based on comparable species and expert judgment to ensure comprehensive coverage.
Standardized fish surveys were conducted during autumn of 2010 and 2022, adhering to the European standard for fish fauna monitoring in lake water bodies [38], to evaluate the density and population structure of fish species. Benthic gillnets (1.5 × 30 m, height × length) comprising 12 panels with varying mesh sizes from 5 mm to 55 mm (knot to knot) were randomly deployed across three distinct depth zones (0–2.9 m, 3–5.9 m, and 6–11.9 m) throughout the whole lake area. The gillnets were set before sunset and retrieved after dawn, resulting in a fishing duration of approximately 12 h. Catches per unit of effort (CPUEs) were calculated for the total benthic gillnet catches, as well as for individual species, using measures of numerical abundance (NPUE, specimens/gillnet) and biomass (BPUE, g/gillnet). To investigate the distribution of fish across various water depths, CPUEs for the benthic gillnet catches were estimated for specific depth zones.

2.4. Data Analysis

2.4.1. Compositional Changes

To estimate the alterations in the lake’s fish fauna composition over the last 12 decades ranging from past conditions (referring solely to native assemblages, i.e., from 1900) to the present, the Jaccard’s index was used, calculated as Jaccard similarity = (number of fish species present in both assemblages/(number in either assemblage), i.e., J(A, B) = |A ∩ B|/|A ∪ B|. This index ranges from 1 to 0, with 1 indicating complete similarity (i.e., identical species composition) and 0 indicating complete dissimilarity (i.e., no shared species between the two assemblages [39]. The above analysis was conducted using R-Studio (packages ggplot2 [40], vegan [41]).

2.4.2. Species Functional Dissimilarity and Changes

To investigate the functional changes in the fish fauna community from the reference conditions of 1900 to 2020, the functional richness (FRic) of both assemblages was estimated as the convex volume generated by the graphic representation of the set of traits of each species of each assemblage [42]. Specifically, we prepared a functional dissimilarity matrix between each pair of species, calculating the Euclidean distances among the functional traits. Then, a Principal Coordinates Analysis (PCoA) was applied to this matrix, allowing for the calculation of the volume of the convex (V) cover of each assemblage (A) (of 1900 and 2020) based on the first three main axes [43]. Thus, V (A1900) and V (A2020) correspond to the convex cover volume of assemblages A1900 and A2020, respectively, while V(A1900 ∩ A2020) corresponds to the volume of the shared or intersected convex hull [44].
To calculate functional b-diversity (FDiv), we used the following algorithm:
FDiv = [(V(A1900) + V(A2020)) − 2 × V(A1900 ∩ A2020)] × [(V(A1) + V(A2) − V(A1 ∩ A2)]−1 [44], where V(A1900) and V(A2020) represent the multidimensional volumes of assemblages A1900 and A2020, and V(A1900 ∩ A2020) represents the multidimensional volume shared by both assemblages [44]. This index measures the difference in functional traits between the two assemblages. The lower value indicates greater similarity in the functional composition between the two assemblages. Then, the functional turnover was calculated. It measures the rate at which species are being replaced in terms of functional traits between the two assemblages. A lower value indicates less turnover in functional composition between the two assemblages. Functional turnover was calculated as the following: FTur = [2 min (V(A1900), V(A2020)) − 2 V(A1900 ∩ A2020)] × [(2 min (V(A1900), V(A2020)) − V(A1900 ∩ A2020))]−1. Subsequently, the nestedness was calculated. This parameter measures the degree to which the species composition of assemblage A2020 is a subset of assemblage A1900 in terms of functional traits. A value close to 0 indicates little to no nestedness, while a value closer to 1 indicates higher nestedness. This was estimated as FNes = [(|V(A1900) − V(A2020)| × V(A1900 ∩ A2020)) × ((V(A1900) + V(A2020) − V(A1900 ∩ A2020))] × [((2 min (V(A1900), V(A2020)) − V(A1900 ∩ A2020)]−1 [44].

2.4.3. Vertical CPUE Differences

An ANOVA analysis (using SPSS) was conducted to test for significant differences between both the numerical and biomass catches per depth zone for each sampling year. To determine which specific depth zones differed from each other, post hoc pairwise comparisons were conducted using Tukey’s HSD (Honestly Significant Difference).

2.4.4. Assessment of the Ecological Quality

The ecological quality of the lake was evaluated using the Greek Lake Fish Index (GLFI), developed following the guidance of the Water Framework Directive (WFD) [45]. This is a two-fish metric index that integrates the relative numerical abundance of introduced species (Introduceda) and the relative biomass of omnivorous species (OMINb), which are responsive to the Lake Habitat Modification Score (LHMS) and water Total Phosphorus concentrations (TP), respectively [45]. The LHMS and TP serve as indicators of overall ecosystem degradation and eutrophic conditions, respectively. Ranging from 0 to 1, the GLFI index assesses ecological quality, with 0 indicating poor ecological quality and 1 indicating high ecological quality. By comparing current conditions to reference conditions, the GLFI aligns with the requirements outlined in the Water Framework Directive (WFD).

3. Results

3.1. Structural Changes

The fish population of Lake Kastoria in 1900 consisted of six indigenous fish species (Table 1). However, 10 more species were introduced by 2020, some of which managed to establish populations (Figure 2).
In the early 1930s, Tinca tinca, Esox lucius, and Perca fluviatilis specimens were introduced to the lake and managed to establish populations [19]. Gambusia holbrooki was probably introduced during the same period to control mosquitoes, according to the misleading perception of that period. In 1985, Carassius gibelio was also intentionally introduced into the lake, and soon after (in the early 1990s) species of the Xenocyprinidae family were introduced to enhance fisheries or for biomanipulation reasons—a practice commonly implemented at many freshwater lentic ecosystems of Greece during that period. It is not known when exactly the species Lepomis gibbosus and Pseudorasbora parva were introduced. The first official record of the last-mentioned species’ presence in the lake was in 2011. However, the species Lepomis gibbosus started being caught by commercial fishers after 2000. Anguilla anguilla was the only native extirpated from the lake due to the construction of large dams downstream of the Aliakmonas River, disrupting river continuity and hindering the species’ reproductive migration.
The Jaccard’s dissimilarity index values were estimated by the comparison of the fish assemblages present in the 1900s, i.e., when the fish assemblage consisted solely of indigenous fish species (Figure 3a). The index’s value was picked in 1990 when most introductions took place (Figure 3b). The index’s value estimated between 1900 and today’s assemblages was equal to 0.615, meaning that approximately 61.5% of the species present today are missing from the assemblage of 1900, and vice versa. This indicates a significant difference or turnover in the species taxonomic compositions between the two time periods.

3.2. Functional Changes

The large-bodied species Silurus glanis exhibited the highest dissimilarity compared to others, while the Xenocyprinids and Esox lucius showed similarities (Figure 4). The introduced species Lepomis gibbosus, Pseudorasbora parva, and Gambusia holbrooki clustered together, while the remaining species, including the middle-sized species favoring the lake’s open waters, formed another distinct group.
The functional richness among the assemblages of 1900 and 2020 was increased due to species introductions (Figure A1, Appendix A). The estimated value of FDiv was 0.8021, indicating a moderate to high level of dissimilarity in functional traits between the assemblages from 1900 and 2020, meaning that the functional composition has changed significantly over time. The estimated value of FΤur was 0.357, indicating a moderate level of functional turnover and suggesting some change in the species compositions and their functional traits between the two time periods. Last, the value of FΝes was 0.446, indicating a moderate level of functional nestedness and suggesting that there is a fair amount of overlap in functional traits between the two assemblages, with a significant portion of one assemblage’s traits being a subset of the other’s.

3.3. Current Species Abundances

The most abundant species in both sampling years was Rutilus rutilus, followed by Perca fluviatilis and Lepomis gibbosus (Figure 5). The estimated mean CPUEs for the year 2022 were at least four times higher than those estimated for the year 2010 for the total catches and at least the first two depth zones (from 0 to 9 m) (Figure 6). In all cases, higher CPUE values were estimated for the shallowest depth zone (0–2.9 m) and decreased towards the deepest depth zone, where there were even estimated values of zero.
The ANOVA results indicated significant differences among the various depth zones for both BPUE (F = 9.601, p < 0.05) and NPUE (F = 11.177, p < 0.05) values in 2010, as well as for NPUE values in 2022 (F = 4.917, p < 0.05). However, for the BPUE values in 2022, the ANOVA did not indicate significant differences among the depth zones (F = 2.078, p > 0.05). Mean BPUE values in 2010 were significantly higher in the depth zone of 0–2.9 m compared to the 3–5.9 m (Tukey’s HSD = 36,063, p < 0.05) and 6–11.9 m (Tukey’s HSD = 61,744, p < 0.05) zones, which were not significantly different from each other (Tukey’s HSD = 25,681, p > 0.05). Similarly, NPUE values in 2010 were significantly higher in the depth zone of 0–2.9 m compared to the 3–5.9 m (Tukey’s HSD = 17.625, p < 0.05) and 6–11.9 m (Tukey’s HSD = 26.333, p < 0.05) zones, which were not significantly different from each other (Tukey’s HSD = 8.708, p > 0.05). Accordingly, in 2022, mean NPUE values in the depth zone of 0–2.9 m were significantly higher compared to those estimated in the depth zone of 6–11.9 m (Tukey’s HSD = 79.200, p < 0.05).

3.4. Ecological Quality Assessment

The ecological quality class estimated using the GLFI index was higher in 2022 than in 2010, categorizing the lake as having “Moderate” quality, and thus providing an upgrade from its previous ‘Poor” condition. This was due to the lowest estimation of omnivorous fish species’ contributions to the catch biomass (Table 2).

4. Discussion

4.1. Compositional Changes

In 1900, Lake Kastoria’s fish fauna comprised only 6 native species; through 2020, an additional 10 species have been introduced, bringing the number of fish species in the lake up to 16. Currently, the species richness is lower after the extinction of the native Anguilla anguilla, while for the introduced species Ctenopharygondon idella, Hypophthalmichthys molitrix, and Hypophthalmichthys nobilis there are no records after 1995. In general, during the examined period (1900–2020) two steep increases in the fish assemblage dissimilarity among decades were observed: one from 1920 to 1940 with the introduction of species such as Esox lucius, Perca fluviatilis, and Tinca tinca to enhance fisheries; and another from 1960 to 1990 when most of the introductions occurred. From 2010 to 2020, the Jaccard’s index values remained at the same level, indicating that the introduced species already present in the lake were adapted and had established permanent populations in the ecosystem. Considering the Jaccard dissimilarity between reference (1900) conditions and present (2020) times, is becoming obvious that the lake’s fish fauna has undergone significant compositional changes that are irreversible, with the establishment of several opportunistic species including Lepomis gibbosus, Pseudorasbora parva, and Carassius gibelio [46,47,48,49].
Such introductions, along with the extinction of native species, emerge as the predominant driver behind the phenomenon of “biotic homogenization” in freshwater fish assemblages on a global scale [50]. This term characterizes the escalating similarity in species compositions among freshwater ecosystems over time [51,52], leading to diminished geographical turnover and historical distinctiveness within these assemblages [53]. This trend is already evident in water bodies across the European continent [54], while taxonomic homogenization has been confirmed for numerous other taxa worldwide [52,55].

4.2. Functional Changes

Within the framework of biotic homogenization, analyzing changes in functional dissimilarity complements the assessment of changes in taxonomic dissimilarity [56]. However, there is not a direct relationship between changes in taxonomic and functional dissimilarity among fish assemblages. For example, a pair of assemblages in a water body over time may show taxonomic differentiation (i.e., an increase in dissimilarity), but could be functionally homogenized if the unique non-native species introduced in each assemblage are functionally similar to the native ones or each other [56].
Regarding the functional traits of the fish fauna, our findings suggest an increase in functional richness over time, which is accompanied by a moderate degree of turnover or dissimilarity between the two time periods (i.e., 1900 and 2020). This phenomenon is linked to the substantial similarity in ecological traits observed among many native and introduced species, indicating heightened niche overlap and interspecies competition. Essentially, multiple fish species in Lake Kastoria’s ecosystem can fulfill similar ecological roles. The analysis of functional similarity/dissimilarity among species and overall functional diversity is necessary to evaluate how the change in species composition may affect ecosystem processes [57].
However, it is important to note that our assessment did not consider the relative abundance of each species in the total fish fauna, nor their changes over time due to the absence of relevant quantitative data from 1900. Incorporating data on species’ abundances could shed light on how functional redundancy is influenced by the prevalence of certain species within the fish assemblage. Ignoring the abundance may mask variations in functional dissimilarity driven by changes in the relative abundance of species performing similar functions. For instance, even if two species have similar functional traits, a substantial increase or decrease in the abundance of one species could still impact ecosystem functioning. Abundance-weighted functional dissimilarity metrics provide a more accurate representation of changes in community structure and functioning [58,59].

4.3. Current Status

The CPUE values estimated in 2010 were among the lowest ever recorded in Greek lakes with this specific research methodology [45]. Given the lake’s significant fishery, this may be attributed to the high fishing pressure exerted on the fish stocks. The higher values estimated in the 2022 samplings may be attributed to the fact that fish populations managed to rebound during the COVID-19 pandemic when the fishing pressure was low in Greek freshwaters due to national restrictions (i.e, the closure of local markets where freshwater fish were sold and a total prohibition of recreational fishing). Such benefits of this “anthropause” [60] could be supported by the higher CPUEs of Perca fluviatilis, which is among the most commercially valuable fish species in the lake’s fishery (after Cyprinus carpio) and follows similar phenomena observed worldwide [60].
The lake’s open waters are dominated by the species Rutilus rutilus, Perca fluviatilis, and Lepomis gibbosus, showing that the last two introduced species outcompeted the native ones. The last-mentioned species is among the most successful invaders of European waters due to its high tolerance and resilience to habitat degradation, pollution, elevated temperatures, and low water levels [46,61].
The consistently higher CPUE values observed in the shallowest depth zone (0–2.9 m), decreasing towards the deepest depth zone, suggest that shallow areas provide more favorable conditions for fish. The low to zero catches estimated in the deepest lake zones are due to the anoxic conditions that prevailed there due to thermal stratification, a phenomenon frequently observed in shallow or highly productive deep lakes, particularly during the summer months [62,63,64,65,66,67,68].

4.4. Ecological Quality Assessment

The most recent ecological quality assessment for Lake Kastoria, classified as Moderate based on fish fauna, aligns with the overall classification of its ecological status according to national biological monitoring data and the WFD provisions [31]. These provisions include the application of the one-out-all-out principle, which implies that the overall ecological quality is defined by the lowest value of the monitored biological quality elements.
The change in the classification of the ecological quality of Lake Kastoria from 2010 to 2022, based on the GLFI fish index, highlights the importance of reassessing the ecological quality of lakes based on fish at regular intervals, as suggested by the WFD. While the differences in species’ relative contributions to total catches in both numerical abundance and biomass between the two sampling periods were relatively small, these changes demonstrate the discriminatory ability of the index. However, CPUEs are snapshots of the fish community and depend on multiple factors [69,70]. Therefore, further research is required to reliably determine if the observed difference in CPUE values is an ecologically significant difference. Nonetheless, the higher GLFI value in 2022 is indicative of a shift in the fish community in favor of non-omnivorous species. This supports the hopeful view that aquatic systems can, under certain conditions, recover and improve their ecological quality.

5. Conclusions

In summary, the study provides a comprehensive analysis of the compositional and functional changes in the fish fauna of Lake Kastoria over the past 120 years. The findings underscore the significant impact of intentional and accidental species introductions on the lake’s biodiversity, highlighting the irreversible nature of these changes and their contribution to biotic homogenization. Despite the increase in functional richness over time, the persistence of moderate turnover in functional traits suggests heightened interspecies competition within the ecosystem. The dominance of introduced species like Perca fluviatilis and Lepomis gibbosus underscores the need for effective management strategies to mitigate their adverse effects on native species. Moreover, the positive shift in the ecological quality, attributed in part to improvements in physicochemical parameters and the resurgence of certain species, emphasizes the potential for ecosystem recovery and underscores the importance of continued monitoring and conservation efforts in urban aquatic ecosystems worldwide. The documented impacts of species introductions and the observed biotic homogenization are phenomena of global concern, reflecting trends seen in numerous other freshwater systems. The findings underscore the critical need for proactive management and conservation strategies to preserve native biodiversity and ecological integrity in the face of ongoing urbanization and species translocations.

Author Contributions

Conceptualization—O.P. and D.C.B.; developing methods—O.P.; conducting the research—O.P.; data analysis—O.P.; data interpretation and preparation of figures and tables—O.P.; writing—O.P. All authors have read and agreed to the published version of the manuscript.

Funding

The lake was sampled in the framework of research programs financed by the following: (1) European Union (European Social Fund) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework Research Funding Program Heracleitus II: Investing in Knowledge Society through the European Social Fund (2) Goulandris Natural History Museum Greek Biotope/Wetland Centre by in the framework of the research project “Fish sampling in Greek lakes”.

Institutional Review Board Statement

The research received approval from the relevant committee in Greece for the conducted fish samplings.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data supporting the findings of this study are available within the paper. For additional information, please contact the corresponding author.

Acknowledgments

This research was co-financed by the European Union (European Social Fund) and Greek national funds through the Operational Program “Education and Lifelong Learning” of the National Strategic Reference Framework Research Funding Program Heracleitus II: Investing in Knowledge Society through the European Social Fund and the Goulandris Natural History Museum Greek Biotope/Wetland Centre by in the framework of the research project “Fish sampling in Greek lakes”.

Conflicts of Interest

The authors declare no conflicts of interest.

Appendix A

Applsci 14 06099 g0a1
Figure A1. The PCoA of fish assemblages from 1900 and 2020 in Lake Kastoria.
Figure A1. The PCoA of fish assemblages from 1900 and 2020 in Lake Kastoria.
Applsci 14 06099 g0a1

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Applsci 14 06099 g001
Figure 1. Location of Lake Kastoria in Greece. The dotted lines represent bathymetric contours and the grey color represents the water surface. Arrows indicate the water’s flow.
Figure 1. Location of Lake Kastoria in Greece. The dotted lines represent bathymetric contours and the grey color represents the water surface. Arrows indicate the water’s flow.
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Figure 2. Fish species presence and absence across decades from 1900 to 2020 based on bibliographic records. Black cells indicate fish species presence in Lake Kastoria.
Figure 2. Fish species presence and absence across decades from 1900 to 2020 based on bibliographic records. Black cells indicate fish species presence in Lake Kastoria.
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Figure 3. (a) Jaccard’s dissimilarity index estimated for fish assemblages from 1900 to the present in Lake Kastoria. (b) Heatmap of Jaccard’s dissimilarity index among decades in Lake Kastoria. The darker the color, the higher the dissimilarity in species composition between the decades.
Figure 3. (a) Jaccard’s dissimilarity index estimated for fish assemblages from 1900 to the present in Lake Kastoria. (b) Heatmap of Jaccard’s dissimilarity index among decades in Lake Kastoria. The darker the color, the higher the dissimilarity in species composition between the decades.
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Figure 4. Fish species’ dissimilarity based on their functional traits, estimated by using Euclidean distance. The darker the color, the greater the dissimilarity.
Figure 4. Fish species’ dissimilarity based on their functional traits, estimated by using Euclidean distance. The darker the color, the greater the dissimilarity.
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Figure 5. Fish species contribution to total benthic gillnet catches (in terms of numerical abundance (NPUE) and of biomass (BPUE)) of the samplings conducted in 2010 and 2022 in Lake Kastoria.
Figure 5. Fish species contribution to total benthic gillnet catches (in terms of numerical abundance (NPUE) and of biomass (BPUE)) of the samplings conducted in 2010 and 2022 in Lake Kastoria.
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Figure 6. Benthic gillnet CPUEs for total catches and per depth zone (i.e., 1: 0–2.9 m, 2: 3–5.9 m, and 3: 6–11.9 m) based on the number of specimens (NPUE, specimens/gillnet) and biomass (BPUE, g/gillnet) in Lake Kastoria. The median (horizontal straight line) and mean (×) values are given. The numbers in parentheses show the number of gillnets that were set in each depth zone.
Figure 6. Benthic gillnet CPUEs for total catches and per depth zone (i.e., 1: 0–2.9 m, 2: 3–5.9 m, and 3: 6–11.9 m) based on the number of specimens (NPUE, specimens/gillnet) and biomass (BPUE, g/gillnet) in Lake Kastoria. The median (horizontal straight line) and mean (×) values are given. The numbers in parentheses show the number of gillnets that were set in each depth zone.
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Table 1. Fish species reported in Lake Kastoria.
Table 1. Fish species reported in Lake Kastoria.
Family SpeciesOrigin
AnguillidaeAnguilla anguilla (Linnaeus, 1758)N
CentrarchidaeLepomis gibbosus (Linnaeus, 1758)A
CyprinidaeCarassius gibelio (Bloch, 1782)A
Cyprinus carpio (Linnaeus, 1758)N
EsocidaeEsox lucius (Linnaeus, 1758)T
GobionidaePseudorasbora parva (Temminck and Schlegel, 1846)A
LeuciscidaeRutilus rutilus (Linnaeus, 1758)Ν
Scardinius erythrophthalmus (Linnaeus, 1758)N
Squalius vardarensis (Karaman, 1928)Ν
PercidaePerca fluviatilis (Linnaeus, 1758)T
PoeciliidaeGambusia holbrooki (Girard, 1859)A
SiluridaeSilurus glanis (Linnaeus, 1758)N
TincidaeTinca tinca (Linnaeus, 1758)T
XenocyprididaeCtenopharyngodon idella (Valenciennes, 1844) A
Hypophthalmichthys molitrix (Valenciennes, 1844)A
Hypophthalmichthys nobilis (Richardson, 1845)A
Total 16
A: alien, N: native, T: translocated. The nomenclature of species and their classification into families are according to the most recent changes [37].
Table 2. Values of the two metrics, OMNIb and Introduceda, estimated for the years 2010 and 2022, along with their respective Ecological Quality Ratios (EQRs) and the total value of the GLFI, indicating the ecological quality class for each year.
Table 2. Values of the two metrics, OMNIb and Introduceda, estimated for the years 2010 and 2022, along with their respective Ecological Quality Ratios (EQRs) and the total value of the GLFI, indicating the ecological quality class for each year.
Parameter20102022
OΜΝΙb60.6946.60
Introduceda51.2249.04
EQR-OMNIb0.320.47
EQR-Introduceda0.440.45
GLFI0.380.46
OMNIb represents the relative biomass of omnivorous species in the benthic gillnet catches. Introduceda represents the relative abundance of introduced species in the benthic gillnet catches.
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Petriki, O.; Bobori, D.C. The Compositional and Functional Diversity of a Mediterranean Urban Lake’s Fish Fauna over the Past 120 Years. Appl. Sci. 2024, 14, 6099. https://doi.org/10.3390/app14146099

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Petriki O, Bobori DC. The Compositional and Functional Diversity of a Mediterranean Urban Lake’s Fish Fauna over the Past 120 Years. Applied Sciences. 2024; 14(14):6099. https://doi.org/10.3390/app14146099

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Petriki, Olga, and Dimitra C. Bobori. 2024. "The Compositional and Functional Diversity of a Mediterranean Urban Lake’s Fish Fauna over the Past 120 Years" Applied Sciences 14, no. 14: 6099. https://doi.org/10.3390/app14146099

APA Style

Petriki, O., & Bobori, D. C. (2024). The Compositional and Functional Diversity of a Mediterranean Urban Lake’s Fish Fauna over the Past 120 Years. Applied Sciences, 14(14), 6099. https://doi.org/10.3390/app14146099

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