Dilution stress facilitates colonization of invasive mosquitofish in a saline Mediterranean stream: population biology response

Abstract

Knowledge of the interplay of abiotic factors and the invasive success of exotic fish is fundamental both to proper management and the ability to predict consequences for native communities. The highly invasive eastern mosquitofish (Gambusia holbrooki) has been introduced worldwide; however, although salinity could limit its invasive success, the influence of variations in water salinity on its population biology has been scarcely studied. The present study aimed to analyse the effect of changes in water salinity on the life history and microhabitat use of a mosquitofish population inhabiting a hypersaline stream subjected to human-caused dilution stress. Dilution process and associated habitat changes, such as increased aquatic vegetation, available food and the spread of invasive riparian vegetation (the common reed Phragmites australis), seem to have favoured mosquitofish proliferation and colonization. Dilution caused an increased somatic condition for all individuals and a higher reproductive investment of males and larger females. This led to greater survival, recruitment rates, and abundance during the period of lower salinity. The species showed changes in microhabitat use which could be advantageous in less saline conditions; for instance, the species preferentially used areas with the presence of P. australis as a refuge, and this pattern increased during the dilution period. These results support the hypothesis that human activity is one of the main forces shaping the colonization and proliferation of exotic freshwater fishes. At least in a Mediterranean context, an increase in mosquitofish abundance and the improvement of its population status could be clear indicators of the degradation of natural saline systems. Copyright © 2012 John Wiley & Sons, Ltd.