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 comprehensively. The FINS II Conference considered the relevance of Top 20 IAS issues (Top 10 threats and opportunities) for Europe determined at the 1st Freshwater Invasiveness – Networking for Strategy (FINS I) conference held in Ireland in 2013. Using a similar format of sequential group voting, threats from FINS I (lack of funding, of awareness and education; poor communication) and several new threats (lack of lead agencies, of standardized management and of common approach; insufficient monitoring and management on private property) were identified by 80 academics, applied scientists, policy makers and stakeholders from 14 EU and three non-EU countries (including 10 invited speakers) during four workshop break-out sessions (legislation remit in both EU/non-EU countries; best management and biosecurity practice for control; data management and early warning; pathways of introductions and citizen science). Identified opportunities include improved cooperation and communication, education and leadership to enhance public awareness and stakeholder participation, systems establishment for early detection, rapid response, monitoring and management of IAS using standardised methods of data collection, storage and usage. The sets of threats and opportunities identified underline the importance of international cooperation on IAS issues in communication, education and funding as priorities, as well as in standardization of legislation, control methods and best practise of research

1. Invasive crayfish are widely acknowledged to have negative effects on benthic food webs in lakes, but few studies have investigated such effects at wider spatial scales and in varying habitats under natural conditions. 2. We examined the effects of introduced signal crayfish (Pacifastacus leniusculus) on the macroinvertebrate assemblages of different habitats in two large boreal lakes. We evaluated whether the density, taxon richness and species composition are altered by the non-native crayfish and whether the responses are similar for stony and vegetated habitats and across a depth gradient. We also studied the influence of crayfish on periphyton biomass at stony sites, as a potential link to changes in macroinvertebrate communities. 3. In both lakes, macroinvertebrate density was similar between crayfish and non-crayfish sites across the habitats and depths studied. However, macroinvertebrate taxon richness was significantly lower, and community composition was altered in the presence of crayfish at stony sites. No similar pattern was detected at vegetated sites or in deeper sublittoral areas. The amount of periphyton was similar regardless of the presence of crayfish, and no clear direct or indirect crayfish-periphyton interaction was detected. 4. Our results suggest that introduced signal crayfish can have negative effects on the littoral macroinvertebrates of large boreal lakes, but that these effects are habitat specific. Our findings highlight how the evaluation of possible effects of invasive species needs to be carried out comprehensively across different habitats and spatial scales if conclusions are to be robust.

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-In Finland, massive signal crayfish introductions started towards the end of 1980s, with an estimated total of 2.2 million signal crayfish been stocked before year 2016. During that period, Finnish fisheries authorities have implemented three national management strategies setting guidelines for the crayfish introductions. The main aims of the strategies have been conservation of native noble crayfish stocks and a controlled spreading of the alien signal crayfish within a designated region. In this study, we report the current distribution of signal crayfish in Finland in comparison to the guidelines set in these three national strategies. The present distribution area of the signal crayfish covers most of the Southern Finland. The signal crayfish has been introduced with a stocking permits to over 480 water bodies. In addition, there have been numerous stockings without permits, which are often next to the region designated for signal crayfish. Based on the results, we conclude that crayfisheries strategies adopted in Finland have only had limited effect on the spread of signal crayfish. We presume that main causes for the uncontrolled spreading of the signal crayfish in Finland have been lack of strict official supervision and general lack of awareness about the risks associated with the alien species spreading.

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Key-words:crayfish, habitat connectivity, invasive species, stable isotopes Several studies have shown that distinct compartments of lake ecosystems are coupled via transportation of organic matter, nutrients and energy across habitat boundaries. Here we evaluate the potential of the invasive signal crayfish (Pacifastacus leniusculus (Dana)) to modify energy pathways in large boreal lakes. Using a stable isotope mixing model and calculation of the isotopic niches we estimated the contribution of different food sources to the diets of crayfish captured from different habitats, and from that inferred their potential to transport energy across the littoralprofundal gradient. The crayfish caught from the littoral area utilized mainly littoral food sources, whereas the importance of profundal sources increased consistently with depth. We also found crayfish in deeper habitats with littoral δ 13 C label, which indicates significant use of littoral sources. These results presents evidence that invasive signal crayfish create a new link in energy transfer from littoral areas to profundal areas and thereby increase connectivity between these spatially distinct habitats. Our results highlight a need for better understanding of the role of crayfish in lake energy dynamics and habitat connectivity. RÉSUMÉ L'écrevisse invasive accroît la connectivité des habitats : une étude de cas dans un grand lac boréal Mots-clés :écrevisses, connectivité des habitats, espèce envahissante, isotopes stables Plusieurs études ont montré que les différents compartiments des écosys-tèmes lacustres sont couplés via le transport de la matière organique, de nutriments et de l'énergie à travers les frontières de ces habitats. Ici, nous éva-luons le potentiel de l'écrevisse signal invasive (Pacifastacus leniusculus (Dana)) à modifier les voies de l'énergie dans les grands lacs boréaux. En utilisant un modèle de mélange des isotopes stables et le calcul des niches isotopiques, nous avons estimé la contribution des différentes sources de nourriture pour l'alimentation des écrevisses capturées dans différents habitats, et déduit leur potentiel de transport d'énergie le long du gradient littoral-zone profonde. Les écrevisses capturées dans la zone littorale utilisent des sources alimentaires essentiellement littorales, alors que l'importance des sources de zone profonde augmente de façon régulière avec la profondeur. Nous avons aussi trouvé des écrevisses dans des habitats plus profonds avec une signature δ 13 C du littoral, ce qui indique une utilisation importante des sources littorales. Ces résultats présentent des preuves que l'écrevisse signal invasive crée un nouveau lien dans le transfert d'énergie à partir des zones littorales vers la zone profonde et donc augmente la connectivité entre ces habitats spatialement distincts. Nos résultats mettent en évidence la nécessité de mieux comprendre le rôle de l'écrevisse dans la dynamique de l'énergie d'un lac et la connectivité des habitats.

The character and magnitude of predation by the invasive, ectothermic Pacifastacus leniusculus, a crayfish widely introduced to Europe and Japan from North America, on the eggs of coregonid fishes, vendace Coregonus albula and whitefish Coregonus lavaretus were examined by experimentation, modelling and field data. The present results showed that P. leniusculus has the potential to be very efficient predator of fish eggs under winter conditions, but the predation by P. leniusculus did not significantly decrease production of coregonid larvae during the years with a high P. leniusculus population in the study lake. Hence, the mortality caused by the novel invertebrate predator appeared to compensate for other yet unexplored mortality factors instead of having an additive effect on the present salmonids.