Invasive crayfish increase habitat connectivity: a case study in a large boreal lake

Abstract

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 introduced signal crayfish and native noble crayfish have different effects on sublittoral macroinvertebrate assemblages in boreal lakes

“…This was mainly due to the 13 Cc range of some lakes where crayfish C signatures indicated wider variation and thus a wider trophic niche. Ruokonen et al (2012) found that individual signal crayfish caught from the littoral in large Lake Päijänne had smaller trophic niche than those sampled from the profundal. Lake Iso-Tarus, which had the largest crayfish C signature range of the study lakes (I), registered low values of sublittoral macroinvertebrate abundance and species richness (III), but among the highest in the littoral, whereas signal crayfish lakes with the smallest crayfish carbon signature range, like lakes Ala-Karkijärvi and Syväjärvi, exhibited an opposite pattern.…”

“…Invertebrate grazers were greatly reduced by crayfish, and indirectly periphyton was positively affected by crayfish. Previous studies reported that invasive crayfish species can also affect littoral benthic fishes (Guan andWiles 1997, Hirsch andFischer 2008), although recent findings (Ruokonen et al 2012) have demonstrated the contrary. Moreover, invasive crayfish represent a severe threat to their native counterparts and in the majority of cases outcompete and replace native species (Nyström et al 2001, Stenroth and Nyström 2003, Bubb et al 2006.…”

“…This difference suggests a somewhat wider overall feeding range for signal crayfish, presumably able to exploit some additional resources or habitats than noble crayfish. Ruokonen et al (2012) have reported that signal crayfish can colonise deeper zones in larger Finnish boreal lakes compared with noble crayfish which prefer the shallower littoral zone (Westman et al 2002). The larger signal crayfish trophic niche width found at species level then led to further investigations to explore the effects of the two crayfish species at a larger spatial scale.…”

Resource polygon geometry predicts Bayesian stable isotope mixing model bias

“…For example, the studies of Semmens et al (2009), Wootton (2012, Cummings & Schindler (2013), and Silva-Costa & Bugoni (2013) explored the contributions of marine and freshwater or terrestrial resources to consumers in spatially subsidized food webs (Polis et al 1997). Jensen et al (2012), Xu et al (2012), and Ruokonen et al (2012) studied benthic−pelagic or benthic−terrestrial systems. However, studying ecotones does not guarantee a well-resolved resource polygon, as many ecotonal food webs were actually poorly resolved.…”

It takes time to see the menu from the body: an experiment on stable isotope composition in freshwater crayfishes

“…SIA has increasingly been used in ecological studies focusing on crayfishes (e.g. Stenroth et al, 2005, Roth et al, 2006Ruokonen et al, 2012;Ercoli et al, 2013;Jackson et al, 2014), which motivated this investigation on how these methods could be applied to specific laboratory conditions and diets. The main aims of our study were 1) to define, under experimental nutritional treatment, the temporal dynamics of the stable isotope ratios in two freshwater crayfishes, the noble crayfish (Astacus astacus, Linné) and the signal crayfish (Pacifastacus leniusculus, Dana), and 2) to assess the effect of controlled, single food type diet on the condition of crayfish.…”