Introduction

The red swamp crayfish Procambarus clarkii (Girard, 1852) is a widely distributed freshwater benthic crustacean, being now considered the most cosmopolitan freshwater crayfish species in the world (Gherardi 2006; Loureiro et al. 2015; Souty-Grosset et al. 2016). Native to northeastern Mexico and the southern USA, it has been introduced in all continents except Antarctica and Oceania (Gherardi 2006; Souty-Grosset et al. 2016). It is ranked in the top three among the ‘‘100 worst’’ alien species in Europe (Netwing et al. 2018) and it is listed as an invasive species of Union concern (European Commission2020). Species included in the Union list are subject to restrictions and measures and most EU countries have banned importation of live crayfish. Due to its biological and behavioral plasticity and dispersal patterns, it can colonize a wide range of environments, from rivers, lakes, reservoirs, ponds and irrigation channels, to brackish lagoons and estuaries (Casellato and Masiero 2011; Dörr et al. 2020; Gherardi 2007; Hobbs et al. 1989; Souty-Grosset et al. 2016). P. clarkii also inhabits terrestrial or semi-natural swamps, terrestrial humid zones, such as meadows or rice fields, and recently it was discovered for the first time in caves in Portugal and Italy (Mazza et al. 2014). It exhibits high rates of reproduction (parthenogenesis with low propagule pressure under some conditions), cyclical dimorphism between two sexual morphotypes not only in males but also in females (Hamasaki et al. 2020), high rates of aggression towards native as well as non-native crayfish species (Veselý et al. 2021), opportunistic feeding behavior, ability to withstand droughts by digging deep burrows (Arce and Dieguez-Uribeondo 2015; Guo et al. 2019) and high dispersion ability (Gherardi 2006; Kouba et al. 2021).

The negative impacts of P. clarkii on native aquatic plants and animals are well documented (e.g., Donato et al. 2018; Loureiro et al. 2015; Souty-Grosset et al. 2016; Twardochleb et al. 2013). Briefly, it acts as a keystone species in food webs, causing a significant decrease in biomass and biodiversity of native communities. It also alters habitat structure and eventually outplaces native as well as non-native crayfish species. Being a carrier of the oomycete Aphanomyces astaci Schikora, which is the causative agent of the ‘crayfish plague’ (Diéguez-Uribeondo and Soderhall 1993), P. clarkii may also lead to mass mortalities of astacids worldwide (Filipová et al. 2013; Martín-Torrijos et al. 2018, 2021; Peiró et al. 2016; Putra et al. 2018).

In Europe, the species was initially introduced from Louisiana to Spain in 1973 and 1974 (Oficialdegui et al. 2019) and during the last 50 years it established populations in at least 18 European countries/territories (Lipták et al. 2023a) through translocations and multiple secondary introductions. The most important vectors of introduction of the species are aquaculture, aquarium trade, accidental escapes from garden ponds, stocks intended for human consumption, or intentional releases to replace other crayfish species (e.g., Anastácio and Marques 1995). Its presence in captivity in Greece was first reported in 2011 (Papavlasopoulou et al. 2014), and despite being banned and listed as invasive species, several color varieties of P. clarkii are sold in pet shops in Greece via the internet. It is also widely present on the aquarium market in other European countries such as Germany, the Czech Republic, Poland, Italy, and Serbia (Lipták et al. 2023b; Maciaszek et al. 2019). The species’ invasiveness risk was assessed as very high globally by AS-ISK (Vilizzi et al. 2021) and for the Eastern Mediterranean (Tarkan et al. 2021) and Greece by FISK (Papavlasopoulou et al. 2014).

In this contribution, the red swamp crayfish P. clarkii is reported for the first time in the wild, in Greece, constituting also the first record for the Balkans.

Methods

Four P. clarkii individuals were found in the mid-lower reach of the Vosvozis River, northeastern Greece (Fig. 1) during a routine EU Water Framework Directive monitoring on 15 May 2023. Specimens were photographed alive on-site and released back into the water (Fig. 2). Benthic habitat was mainly composed of gravel and sand, silt, and mud, and abundant filamentous algae, thus indicating eutrophic conditions. The fish fauna at the location is mainly represented by the Orpheus dace Squalius orpheus, the Bulgarian spined loach Cobitis strumicae, the Black Sea chub Petroleuciscus borysthenicus, the eastern mosquitofish Gambusia holbrooki, and the Prussian carp Carassius gibelio, and with lower numbers by the Aegean gudgeon Gobio bulgaricus, the critically endangered cyprinid Alburnus vistonicus, and the round-scaled barbel Barbus cyclolepis. There are no historical or present data related to any population of non-indigenous crayfish species in water bodies of the entire catchment area.

Fig. 1
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Collection site of P. clarkii in Vosvozis River, Thrace (Greece)

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Fig. 2
figure 2

P. clarkii female individuals from Vosvozis River, Thrace (Greece)

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Vosvozis River is situated in the eastern part of Eastern Macedonia and Thrace Region, northeastern Greece, near the city of Komotini. With the catchment area of 340 km2, this river has a total length of 53 km and discharges into the Ismarida Lake before entering the Thracian Sea (the northernmost part of the Aegean Sea). The main and most significant pollution sources come from industrial activities which discharge their wastewater directly into the river or in its tributaries, without any treatment by the domestic wastewater treatment plant of the city of Komotini and by private septic tanks (half of the population, 70,000 inhabitants, is served by such systems).

Physicochemical parameters at the sampling location were measured with a HANNA multiparameter water quality meter (HI98194, USA), while water samples were collected and transferred to Hellenic Centre for Marine Research (HCMR) laboratories for nutrient and major ion analysis.

Results and discussion

The physicochemical and habitat characteristics of the sampling locality are presented in Table 1. Water quality of the sampling site was poor, as classified according to the relevant quality index (Skoulikidis et al. 2006).

Table 1 Physicochemical and habitat characteristics of the P. clarkii collection site in Vosvozis River, Thrace (Greece)
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The particular reach of the Vosvozis River, where the individuals of P. clarkii were found, has been monitored for eight consecutive years since 2015 and the crayfish has never been previously detected. The coloration of the four individuals represents the ‘neon red’ crayfish aquarium breed, which is exclusively tank-raised. Based on its coloration, we came to a conclusion that the individuals were released by an aquarium hobbyist, possibly from Komotini city (c.f., Maciaszek et al. 2019), and survived at least until collection in the environment. However, during the subsequent sampling campaign of September 2023, where eight crayfish traps were deployed in a 200 m river stretch, no individuals were found. Thus, intensive and long-term monitoring of the river basin with both conventional field surveys and advanced molecular techniques such as the eDNA method, are needed to investigate (1) whether there is a viable and established population of P. clarkii in the river, and (2) whether the individuals previously migrated to/from Ismarida Lake, which is located few kilometers downstream from the sampling location, or any other upstream segments (Fig. 1). Once introduced in the wild, its spread is expected to be rapid through natural and/οr anthropogenic dispersal, as indicated by the available literature (Gherardi 2006; Kouba et al. 2021). When detected, the management measures can include local removal with traps to lower the intraspecific density, hence lowering the tendency of a population to further spread. A targeted information campaign for the impacts of P. clarkii on aquatic species and ecosystems, but also for accompanied monetary costs (Kouba et al. 2022) are necessary to prevent secondary introductions. Yet, the ultimate eradication of the species is rarely achieved especially in riverine environments (e.g., Lidova et al. 2019). Therefore, public awareness and communication are also essential for preventing further species’ introductions and translocations (Lipták et al. 2023c). Moreover, on the country-level, the predominant focus should be directed to the strict monitoring and control of illegal crayfish imports via the aquarium trade.