Not Only Environmental Conditions but Also Human Awareness Matters: A Successful Post-Crayfish Plague Reintroduction of the White-Clawed Crayfish (Austropotamobius pallipes) in Northern Italy

Raoul Manenti,Alessandro Nessi,Benedetta Barzaghi,Mauro Villa,Gentile Francesco Ficetola,Sara Cioccarelli

doi:10.3389/fevo.2021.621613

Abstract

In Europe, invasive freshwater crayfish are not only changing freshwater ecosystems, but they are also leading to local extinctions of native freshwater crayfish. This is particularly evident for the populations of red swamp crayfish and spiny-cheek crayfish in northern Italy, which are threatening the last and isolated populations of the white-clawed crayfish. Here, we describe the steps that accompanied a successful reintroduction of the white-clawed crayfish in an Italian stream (Park Monte Barro) that, although isolated from other freshwater sites, suffered from an illegal introduction of the spiny-cheek crayfish in 2013. After the removal of presumably all the introduced spiny-cheek crayfish individuals, we started periodical surveys (twice a year) of the stream to confirm the absence of further introductions and to monitor environmental conditions. Prior to the reintroduction of the white-clawed crayfish that started in autumn 2018, we developed an intense dissemination activity to raise awareness of white-clawed crayfish features and importance among landowners surrounding the stream, including those suspected of the introduction of the spiny-cheek crayfish: we organized public meetings and we performed seven direct visits, house to house, to the local people providing information on good practices for white-clawed crayfish conservation. From 2018 to 2020, every autumn, we reintroduced a batch of 3-month-old white-clawed crayfish juveniles, and we developed a program for the monitoring of crayfish growth and density, water quality, and direct landowners’ disturbance of the site. We detected a significant increase of the white-clawed crayfish total length (TL) from the first reintroduction (October 2018) to June 2020. In 2020, crayfish were consistently larger than in the 2019 surveys; some of them were able to breed less than 2 years after the first reintroduction. In 2020, the estimated density of large crayfish reached 0.57 individuals/m2, which is lower than the density observed prior to extinction. We did not detect any case of human disturbance of the site. Our results underline that the reintroduction actions could be more effective when the stakeholders having the greatest potential impact on the species are identified, informed, and involved as primary caretakers of the activities.

Highlights

Crayfish species are important components of freshwaters’ biodiversity, which play key roles in the food web and can provide important services for aquatic ecosystems (Gherardi et al, 2003; Manenti et al, 2019b; Unger et al, 2020)
Post-reintroduction surveys showed that white-clawed crayfish reintroduction in San Michele creek was successful; the intense dissemination activity was crucial in avoiding further introduction of alien crayfish and prevented disturbance by local stakeholders
extended biotic index (EBI) score remained substantially unvaried over 12 years, confirming that the stream was and remained unpolluted, providing appropriate environmental conditions for the white-clawed crayfish; even the potential organic enrichment caused by local stakeholders when feeding tadpoles did not seem to have altered water quality

Summary

Introduction

Crayfish species are important components of freshwaters’ biodiversity, which play key roles in the food web and can provide important services (e.g., nutrient recycling and structural diversification) for aquatic ecosystems (Gherardi et al, 2003; Manenti et al, 2019b; Unger et al, 2020). Freshwater crayfish have a relevant economic and cultural value; their management, has an impact on the preservation of food resources and cultural heritages (Gherardi and SoutyGrosset, 2006; Manenti et al, 2019b). This relevance for humans has heavily shaped the geographical distribution of some European species because of human activities and humanmediated translocations (Souty-Grosset et al, 1997, 2006). With the recent observation of the cambarid Cambarellus patzcuarensis in Hungary, the Central and Western European indigenous crayfish species have been strongly outnumbered by non-indigenous species (Weiperth et al, 2017, 2020)

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