The signal crayfish Pacifastacus leniusculus Dana, 1852 is a successful invasive species in the Iberian Peninsula. This is of particular conservation concern, as fish fauna is highly endemic and also threatened within this ecoregion. The aim of this study was to analyze behavioral interactions and trophic overlap between signal crayfish and native fishes in Iberian rivers (northern Spain). Video cameras were used to record fish “dominance/evasion” after spatial encounters with crayfish. Diet composition and isotopic signatures (δ13C and δ15N) were compared to evaluate the niche overlap. Fish were dominant in 25% of the encounters with juvenile crayfish, whereas this percentage was only 4% with adult crayfish. Observations showed a high fish “evasion” response for Pyrenean stone loach Barbatula quignardi (Bǎcescu-Meşter, 1967) (>30%). Dietary results showed a high trophic overlap between signal crayfish with the pelagic Pyrenean minnow Phoxinus bigerri Kottelat, 2007 and the benthic loach. However, the isotopic niche overlap was low, with brown trout Salmo trutta L., 1758 showing the highest area (only 0.1 ‰2). Overall, our findings suggest that interferences may occur with native species for food (i.e., benthic invertebrates). Consequently, measures should be applied to control invasive crayfish in Iberian rivers.

The identification of habitat requirements of invasive species is essential to evaluate their spread and to assess the vulnerability of recipient ecosystems. We studied the distribution and abundance of the invasive signal crayfish (Pacifastacus leniusculus) in 43 sites in northern Spain and analysed the relationships with several abiotic and biotic parameters of the aquatic ecosystems. Our results indicated that the abundance of signal crayfish was positively associated with vegetation cover and negatively associated with boulders. Also, its abundance was positively correlated with water temperature, organic matter, cations (e.g. sodium), anions (e.g. sulfates) and abundance of some native fish species (Parachondrostoma miegii and Luciobarbus graellsii). We concluded that the habitat of signal crayfish is among salmonid stretches (headwaters) with cold waters and low proportion of organic debris, and among cyprinid stretches (low waters) with warmer waters which it inhabits with another invasive crayfish, the red swamp crayfish (Procambarus clarkii). Our analysis indicated that the presence of signal crayfish is limited in the uppermost stretches by lower water temperatures and a lower proportion of organic debris. The existence of a natural environmental limiting factor in upstream reaches facilitates the conservation of aquatic ecosystems and native fauna.

Environmental conditions and host features that influence the abundance of an exotic branchiobdellidan were studied. One of the most widespread invasive crayfish species in Europe is the signal crayfish, Pacifastacus leniusculus (Dana, 1825). Along with this invasive crayfish, other alien species that live on the crayfish's body surface, such as bacteria, algae, fungi and invertebrates, were introduced. One of these symbiont species is a branchiobdellidan worm, Xironogiton victoriensis (Gelder and Hall, 1990). Because a previous study identified this exotic branchiobdellidan in 3 different and spatially separate populations of the red swamp crayfish, Procambarus clarkii (Girard, 1852), an investigation into the factors affecting its abundance was necessary. We sampled 1817 sites between 2005 and 2013 in the Ebro Basin (Spain), and the distributions of X. victoriensis and P. leniusculus were represented and interpreted. Furthermore, we sampled 2914 crayfish from 43 Spanish localities to investigate the influence of environmental conditions and host features (sex, body size, body condition, density and ecdysis) on the abundance of X. victoriensis. The abundance of the branchiobdellidan was higher in the largest individuals and in those showing the best body condition. The crayfish body condition (or welfare) increased significantly with the branchiobdellidan infestation, suggesting that mutualism is the biological relationship between X. victoriensis and P. leniusculus. Although 91.04% of the adult signal crayfish were infested with X. victoriensis, only 59.3% of the juveniles were infested. Nonmolted crayfish had higher branchiobdellidan abundance than that of recently molted host specimens; however, the abundance of the symbiont did not differ between sexes and host densities. Finally, biochemical oxygen demand, phosphates, coliforms, and potassium were positively related with the branchiobdellidan abundance. The relationships between some environmental variables and the abundance of branchiobdellidans have not been previously well studied, and these findings will be important for risk assessments and models predicting the spread of exotic branchiobdellidans.

Invasive alien species present a global threat to biodiversity, particularly where pathogens and symbionts are involved. Branchiobdellidans are clitellate annelids with an obligate ectosymbiotic association primarily on astacoidean crayfish. There are several examples of branchiobdellidan species adopting a geographically exotic host where endemic and exotic crayfishes cohabit the same water body. The first records of a western North American branchiobdellidan, Xironogiton victoriensis, adopting the eastern North American crayfish, Procambarus clarkii, in 2 river basins in Spain provide further evidence of the ectosymbionts’ tolerance to adopt an exotic host. Given worldwide translocations of these and other commercial crayfish species, limnologists and agency managers need to be alert for further introductions of X. victoriensis and other branchiobdellidans. Impacts of these exotic ectosymbionts on habitat and biota at a new location are unknown, as are their consequences on native biodiversity.

Review of the state of knowledge of crayfish species in the Iberian Peninsula This paper reviews information relevant to managing the four crayfish species present in the Iberian Peninsula. The red swamp crayfish, Procambarus clarkii, signal crayfish, Pacifastacus leniusculus, and Yabbie, Cherax destructor, are classified as invasive alien species by Spanish legislation. The most significant negative impacts of these species in freshwater ecosystems are noted, and some management methods are proposed. In addition, scientific studies addressing the origin and taxonomy of the Iberian white-clawed crayfish, Austropotamobius italicus italicus, are discussed. The Iberian populations of A. i. italicus have been severely diminished since the onset of the expansion of the aphanomycosis disease in 1978. However, this trend began to undergo reversal a few years ago, and the populations of this species are now growing. Finally, current legislation concerning the fishing and conservation of crayfish species is explained and discussed.