Predation assessment of the invasive ctenophore Mnemiopsis leidyi in a French Mediterranean lagoon
Résumé
Abstract Since 2000, the invasive ctenophore Mnemiopsis leidyi has been recorded in Mediterranean brackish lagoons. Quantitative data on its feeding behavior (i.e. potential ecological impact) in these particular environments are non-existent. In this study, we describe in situ predation dynamics of M. leidyi in the Berre Lagoon (south-eastern France) over a 22-month survey. Ctenophores were fixed in a solution of formalin in brackish water, allowing the study of the prey items in the gastric cavities at different time scales. The number of prey items ingested is influenced by the ctenophore biovolume, from 8 (0.5 mL) to 1 207 prey ind−1 (35 mL), and by temperature of 3.4°C (2 ± 2 prey ind−1) to 23.2°C (517 ± 295 prey ind−1). Gut evacuation time is strongly related to temperature and ranged from 80 (25°C) to 160 min (9°C). Mnemiopsis leidyi diet changed seasonally following in situ concentrations of prey. The less mobile preys such as mollusks and barnacles were the most impacted. The ctenophore predation pressure on the zooplankton assemblage could lead at time to a release of grazing pressure on phytoplankton and favor the eutrophication of the lagoon.