Naturalised populations in estuaries are characteristic of non-native species tolerant to the salinity gradient. The non-native isopod Synidotea laticauda, since the first record in 1991 in a European estuary, has been continuously recorded in others (e.g. in 1994 in the Guadalquivir estuary). Possible links between physiology and its successful establishment in the Guadalquivir estuary were explored through the combination of physiological studies and field distribution (7 years). Survival, osmoregulation and potential respiration rate were estimated under different experimental salinity conditions. This non-native species is naturalised, with presence of juveniles and adults during most of the year. Spatial patterns were closely related to the salinity gradient showing the highest densities at its isosmotic point (salinity = 20). Survival experiments showed a high tolerance (survival > 80%) to salinity changes between 5 and 35 and no mortality close to its isosmotic point. In addition, acute salinity changes had a clear effect on the potential respiration rate. Overall, our results suggests that the weak osmoregulatory capacity of S. laticauda determined its salinity-dependent distribution pattern, showing high densities at physiologically more favourable salinities, minimizing the energy required for osmoregulation and therefore its mortality risk.

This study was funded by the European Fisheries Fund through the Regional Government of Andalusia (Consejería Agricultura, Pesca y Desarrollo Rural, Junta de Andalucía). EGO was funded by the Juan de la Cierva Research Program (MINECO-Ministerio de Economia, Industria y Competitividad) and CEI-MAR (International Campus of Excellence of the Sea).