Data description: Data were extracted from the OLA observatory (© SOERE OLA-IS, INRA of Thonon-les-Bains, SILA, [1974-2016], developed by the Eco-Informatique ORE system of the INRA) in April 2020.

Data consists in Dreissena sp. veligers density (individual/m2) estimated in the pelagic area of Lake Geneva from 2006 to 2019.

<Data were collected in Lake Geneva during the long-term monitoring program co-funded by the CIPEL and INRAE.

These data have been used in the paper by Haltiner et al. 2022.

Data acquisition: Samples were collected at a pelagic station, SHL2, in Lake Geneva (France-Switzerland) according to the protocols described in Rimet et al. https://doi.org/10.4081/jlimnol.2020.1944 . Dreissena veligers were collected using a 200µm plankton net during a vertical tow from 50m to the surface. The samples were preserved in a 5% buffered formaldehyde solution.

Data processing: Data were processed according to the protocols described in Rimet et al. https://doi.org/10.4081/jlimnol.2020.1944. Veligers were identified and individuals were enumerated in sub-samples that contains at least 0.1ml zooplankton. Veligers abundances were given as the number of individuals per square meter and were their densities were calculated by using the formula:

Veliger abundance = N_SubSample×V_Sample/V_SubSample ×H_filtred/V_filtred

Where N_SubSampleis the number of veligers in the sub-sample, V_(Sample )is the volume of the sample, V_SubSample is the volume of the sub-sample, H_filtredis the height of the sampled water column (50m) and V_filtred is the volume of water filtered by the net (4.81m3).