Species introductions are widely reported as a major threat to biodiversity conservation in Natura 2000 sites. Pumpkinseed Lepomis gibbosus was introduced in Europe in the late 19^th century and is currently listed as Invasive Alien Species of Union concern. To assess its potential impact on the native freshwater communities of Cyprus, we investigated pumpkinseed distribution and diet within 21 Natura 2000 sites. Pumpkinseed occurred in 15 out of the 22 surveyed reservoirs (68.2%), while it was recorded in only four of the 26 investigated rivers (15.4%), likely due to water availability, habitat constraints and physical barriers. Overall, this non-native fish was recorded in 12 Natura 2000 sites (57.1%). Diet analysis showed a preference for chironomid larvae, molluscs, and crustaceans, with evidence of ontogenetic dietary shifts. Fish were a minor prey, while there was no evidence of predation on reptiles or amphibians, suggesting that the impact of pumpkinseed on the conservation of native aquatic vertebrates may be negligible. Surveys also allowed to record several non-native fish species, including some predators, e.g. largemouth bass Micropterus salmoides, pikeperch Sander lucioperca and channel catfish Ictalurus punctatus, the diet and potential impact of which should be carefully assessed. This study highlights the importance of monitoring to mitigate the spread of non-native fish and support conservation within protected areas.

Biodiversity, diet, non-native species, protected areas, reservoirs

The Natura 2000 European Ecological Network was designed to support the conservation of vulnerable natural habitats and threatened species throughout the European Union (EU). The network includes Special Areas of Conservation (SACs) and Sites of Community Importance (SCIs), designated under the EU Habitats Directive (92/43/EEC), as well as Special Protection Areas (SPAs), designated under the EU Birds Directive (2009/147/EEC). The effectiveness of conservation measures aiming at halting the deterioration of biodiversity depends on several drivers of change; among them, “invasion by species”, that is the successful establishment of introduced species, is one of the most frequently reported “pressures” (negative drivers of change) by EU member states (Maes 2013; Early et al. 2016; Seebens et al. 2017; Rabitsch et al. 2020). In response, in 2014 EU institutions introduced the Regulation 1143/2014, aimed at preventing and managing the spread of invasive alien species (IAS: non-native species that spread and cause a significant change in ecosystem processes or severe economic losses; Copp et al. 2005). As protected areas aim to conserve key elements of biological diversity, the impact of IAS in Natura 2000 sites is considered more detrimental than elsewhere (Foxcroft et al. 2014).

The introduction of fish species is widely recognised as a major driver of freshwater ecosystem alteration (Moyle 1997; Cowx 1998; Dudgeon et al. 2006; Leprieur et al. 2009; Strayer 2010). While the first introductions probably date back to Roman times, a peak was recorded between the end of the 19^th century and mid-20^th century (Welcomme 1988). River systems facilitate the spread of non-native species often resulting in substantial ecological (Cucherousset and Olden 2011) and economic (Cuthbert et al. 2021) impacts. Efforts to combat their spread and mitigate associated damages cost billions of US dollars annually (Diagne et al. 2021).

One of the most introduced aquatic species worldwide is the North American pumpkinseed Lepomis gibbosus (García-Berthou et al. 2005), which was first brought to Europe in the 1880s (Maes 1898), through the so-called Perpignan–Barcelona corridor (Yavno et al. 2020). Over the past century, it has been released, accidentally or deliberately, in several water basins in the EU and is now established in all member states except for Estonia, Malta and Sweden (Copp and Fox 2007). The reasons for its introduction are manifold: for angling in France, as forage for introduced predator fishes in Iberia, as an ornamental pond fish in England, and as an aquarium species in many other countries (Elvira 2001). Sometimes it has been inadvertently transferred between water bodies along with intentionally stocked species, such as young-of-year carp, Cyprinus carpio, or native aquatic plants (reviewed by Zięba et al. 2020). Its high establishment success has been attributed to its tolerance to harsh environmental conditions, such as high temperatures and hypoxia (Farwell et al. 2007), as well as its high reproductive success and generalist feeding habits (Cucherousset et al. 2009).

The pumpkinseed has been reported to affect native fish (Welcomme 1988), and amphibians (Bosman 2003; Préau et al. 2017), including endangered species listed in the Habitats Directive (Rabitsch et al. 2020). There is also evidence of considerable declines in native invertebrate communities, freshwater larvae of odonates, heteroptera, diptera and trichoptera showing the greatest declines (Janssen 2000; van Kleef et al. 2008). Due to its extensive ecological impact, the pumpkinseed is classified as an “ecosystem-altering” species and ranks among the top ten introduced fish species with adverse ecological effects (Casal 2006). In 2019, it was added to the list of invasive alien species of Union concern developed under Regulation (EU) 1143/2014.

Because of widespread availability of reservoirs, which possibly promoted its establishment and dispersal (Fox et al. 2007), in southern Europe the pumpkinseed is associated with severe ecological changes and economic losses (Elvira 1998). At the southernmost edge of the EU, Cyprus is recognised as a biodiversity “hotspot” (Myers et al. 2000). The most updated (July 2024) list of Annex I and II species includes 14 plants, 19 mammals, 3 amphibians and 11 reptiles, of which 5 are (semi-)aquatic species: Hyla savignyi, Pelophylax bedriagae, Bufotes cypriensis, Mauremys rivulata and the critically endangered Natrix natrix cypriaca (Georghiou et al. 2024). To enhance the conservation of its species and habitats, the Republic of Cyprus has designated, until now, a total of 69 Natura 2000 areas, of which 36 are designated under the Habitats Directive, 26 under the Birds Directive and 7 under both Directives. Notwithstanding, the freshwater network of Cyprus also hosts up to 20 established non-native fish species (Elvira 2001; Hadjisterkotis 2008), of which 12 – including the pumpkinseed – have been confirmed by recent surveys (Zogaris et al. 2012; I.A.CO 2022). Additionally, two other IAS of Union concern, the pond slider Trachemys scripta and red swamp crayfish Procambarus clarkii, occur in 44 inland lentic and lotic water bodies across the island (Papatheodoulou et al. 2021). Knowledge gaps still exist regarding the potential impacts of these IAS on native freshwater communities of Cyprus. As a preliminary step to assess the consequences of introductions on conservation efforts, we investigated the distribution and diet of pumpkinseed in lentic and lotic water bodies within 21 Natura 2000 sites. Sampling was conducted in rivers using electrofishing and in reservoirs using both nets and electrofishing in shallow waters. Diet analysis aimed at assessing the potential impact of pumpkinseed, specifically on species of conservation interest.

Although the occurrence of introduced species in protected areas has progressively increased since the 1980s, their impact has been long underestimated by relevant authorities, hindering the implementation of effective management actions (Usher 1988; Monaco and Genovesi 2014). Although Cyprus started to join the Natura 2000 network in 2004 and currently ranks among the top EU countries in terms of percentage of land area covered by this network (European Environmental Bureau 2018), our results demonstrated that efforts to fully implement the Habitats Directives have not allowed to prevent the occurrence of non-native species of Union concern in freshwater habitats. Together with largemouth bass, the pumpkinseed was widespread throughout the study area and in half the surveyed protected sites. The co-occurrence of these two North American Centrarchidae suggests that the latter may have been unintentionally introduced with largemouth bass stocks, which are highly appreciated by anglers.

The relatively small number of large-sized pumpkinseed recorded may suggest two mutually non – exclusive hypotheses: 1) the species reaches sexual maturity early during development, as reported for other low-latitude populations (Copp and Fox 2007), and 2) populations are regulated by predatory fish. Our observations provide some support to the second hypothesis as small individuals (<75 mm) tended to concentrate near the banks, wherever littoral vegetation or the rocky substrate provide some cover from predators, while large pumpkinseed occurred in the water column, where they may be more susceptible to predation by largemouth bass, pikeperch Sander lucioperca and catfish (Hart 1997).

While pumpkinseed populations may be regulated by inter and intra-specific predation in lentic waterbodies, their spread in tributaries appears to be hindered by both habitat requirements and presence of physical (waterfalls) or artificial barriers that affect longitudinal connectivity. Reservoirs typically overflow only during the short, rainy season, which may allow the downstream spread of non-native fish. This “drip-feeding” of river stretches from upstream waterbodies has also been reported for England, where, however, the species remains confined to lentic waters (Copp and Fox 2007). In Cyprus, the ephemeral regime of most effluent watercourses, which often dry in summer, may control pumpkinseed expansion. Nevertheless, localized, pumpkinseed populations may still exist in permanent or intermittent rivers, wherever environmental conditions are suitable. As an example, the species was recorded in the River Pediaios, which slowly flows through the centre of Nicosia, where it was likely introduced as an ornamental fish. To prevent pumpkinseed expansion, potentially suitable areas where the species may be released voluntarily should be mapped and regularly monitored by electrofishing or eDNA analysis, a non-invasive, time – and cost-efficient method for biomonitoring (Darling and Mahon 2011).

Given the currently negligible occurrence of the species in watercourses, the diet we recorded reflects the feeding habits of the species in lentic waterbodies. As previously reported for other Mediterranean areas of introduction, chironomid larvae formed the bulk of pumpkinseed diet (Rodriguez Jiménez 1989; Godinho et al. 1997; Domínguez et al. 2002; Gkenas et al. 2019, 2021). Molluscs, which are a major food item in the species’ native range (Keast 1978; Osenberg et al. 1992), and crustaceans, mainly red swamp crayfish, also contribute significantly to the diet. As reported in European introduction areas, from England (Copp et al. 2002, 2010) to Spain (Almeida et al. 2009) and Hungary (Guti et al. 1991), fish were a minor prey, while there was no evidence of predation on reptiles or amphibians. We also found no evidence that large individuals are more piscivorous than average-sized individuals, with the smallest individual containing fish remains in its stomach being 85 mm long. However, the contribution of fish to pumpkinseed diet was higher than average (mean F% = 1.0; reviewed by Collar et al. 2009). Increased piscivory may occur when macrobenthos availability is low, which could also explain the relatively high (≈ 15%) contribution of terrestrial invertebrates to the diet of large pumpkinseed. The preference for terrestrial food resources shown by large individuals (> 100 mm; see also Godinho and Ferreira 1998) further confirms the ontogenetic variation in this species’ diet (Keast 1978; García-Berthou and Moreno-Amich 2000).

Net-surveys allowed to assess the overall composition of the fish communities of reservoirs, with five species – channel catfish, common roach, pikeperch, largemouth bass and pumpkinseed – occurring in nearly all surveyed waterbodies. Although, considering both its diet and mean body length, the pumpkinseed is not expected to impact the conservation of other aquatic vertebrates, the diet and potential impact of other predators, e.g. largemouth bass (Hodgson and Kitchell 1987), pikeperch (Pérez-Bote and Roso 2009) and channel catfish (Heard 1958; Hilling et al. 2016) should be carefully assessed. As an example, non-native fish predators may have contributed to the decline, and hinder the recovery, of Cyprus grass snake N. natrix cypriaca (Blosat 2008), whose range (ca. 70 km²; Zotos et al. 2021) currently overlaps with three of the surveyed waterbodies: Xyliatos, Aftelotos and Paralimni. Although it is currently difficult to envision the eradication of non-native fish from Natura 2000 sites, especially considering the socio-economic implications, protected areas may help mitigate their impact on native species and ecosystems. The most cost-effective strategy is to prevent introductions through public awareness-raising campaigns (Wittenberg and Cock 2001; Pyšek et al. 2014). Since many reservoirs in protected areas are used for angling, it is crucial to avert the introduction of species into waterbodies where they do not yet occur. Natura 2000 areas can also play a key role in disseminating information on biological invasions, given the great public interest in these areas. Awareness on introductions may also be raised through the involvement of anglers in monitoring and management activities. Furthermore, to increase habitat availability for native aquatic species, a network of ponds of varying sizes could be created within protected areas (Dickman 2012; Innes et al. 2019). These ponds should be disconnected from the hydrographic network, to prevent the spread of non-native species, and could house vulnerable native species for aiding their recovery and conservation.

The authors express their gratitude to the officers of the Water Development Department, Polina Polykarpou, Iakovos Tziortzis, Gerald Dörflinger and Constantinos Moustakas, from the Department of Fisheries and Marine Research, for their invaluable support and data provision.