Abiotic factors affecting habitat selection by two invasive gammarids Dikerogammarus villosus and Pontogammarus robustoides

Abstract

Identification of habitat preferences of invasive organisms is crucial for predicting their distribution and impact. We conducted laboratory experiments to determine preferences of Dikerogammarus villosus and Pontogammarus robustoides, invasive in Europe, with regard to ionic content (450 and 830 μS/cm in a Y-maze), flow (0–30 cm/s in a flow-through tank with stagnant water refuges) and temperature (a gradient 5–35°C). D. villosus selected the lower salinity, whereas P. robustoides did not discriminate between salinities, suggesting that, the raised ionic content in large European rivers cannot explain their absence in small tributaries, as previously postulated. Gammarids never preferred flowing over stagnant water, but could stay in a flow ≤10 cm/s without behavioural changes. They avoided flow ≥15 cm/s. Gammarids selected warmer water than their acclimation temperatures. Temperature selection by D. villosus was related to its acclimation temperature. The choice of P. robustoides depended on the season: it preferred a lower temperature in summer than in autumn. Therefore, its thermal preferences were more stable throughout the year, which might be advantageous in shallow, thermally variable areas. Gammarids used environmental variables to select warm, lentic, freshwater locations, which may help them locate an optimum microhabitat and thrive in temporally and spatially variable environments.