Resilience of alpine lakes invertebrates after the eradication of introduced brook trout Salvelinus fontinalis

Alien fish have been introduced into once fishless mountain lakes worldwide, seriously affecting native biota. In the Gran Paradiso National Park (GPNP, Western Italian Alps), the brook trout (Salvelinus fontinalis) was introduced in several alpine lakes, where it dramatically affected the entire ecosystems, thus leading the GPNP to undertake an eradication campaign, within the EU financed LIFE+ BIOAQUAE (Biodiversity Improvement of Aquatic Alpine Ecosystems) project. The eradication started in June 2013 in three small lakes (depth range: 3-7.4 m) and one large lake (depth: 22.1 m). Intensive gill netting and electrofishing have been used as non-invasive eradication techniques, without lethal effects for native species, potentially including taxa deserving special attention under a conservation point of view. The effects of the eradication are being monitored along with the eradication campaign, comparing the lakes subject of the eradication project with a set of control lakes (both naturally fishless lakes and lakes still containing brook trout) as a reference to quantify the ecosystem resilience using littoral macroinvertebrates and pelagic zooplankton as indicators of the ecological resilience. At its fourth field campaign (June-September 2013-2016) the removal of introduced fish enabled the recovery of many invertebrate taxa. In particular many benthonic and nektonic macroinvertebrates (Plecoptera, Etreroptera, Coleoptera, Tricoptera, Acarina), which were previously absent, rapidly recolonized the lakes, while the large bodied zooplankton crustacean Daphnia longispina (which was under a strong predatory selection) has returned to dominate the zooplankton community of the lakes. These results show the high resilience potential of the invertebrate fauna of alpine lakes after fish eradication and encourage management and conservation authorities to undertake new eradication projects.