Urbanization Rate, Copper Concentration and pH Affect Hydrae Communities' Presence and Abundance

Global change affects all ecosystems worldwide, particularly aquatic communities. Yet, the separate and combined effects of environmental parameters linked to global change remain poorly understood, probably because their effects depend on the precise environmental factors, on their interaction, and on the taxa. Here, we investigated the presence and abundance of 3 Hydra species (Hydra oligactis, Hydra vulgaris and Hydra viridissima) in relation to pH, copper concentration, water and air temperatures, waterbody surface and the proportion of impervious surface around each of 49 sites from 20 ponds sampled in the Parisian region. Not surprisingly, many environmental parameters were correlated. We further expected Hydra presence and/or abundance to vary according to some environmental parameters. In particular, due to the hormetic effect of copper (i.e., beneficial at low and toxic at high concentrations) and to the complex relations between pH, temperature and metal toxicity, we expected an interactive effect of these factors on Hydra presence and/or abundance. Though we did not detect any such interactive effect, Hydra presence decreased with increasing pH and with the proportion of impervious surface, while Hydra abundance increased with increasing copper concentrations, suggesting that these concentrations may fall in the lower range of beneficial effects. Our correlative work underlines the need for extensive studies on the ecological and evolutionary consequences of environmental changes in aquatic ecosystems at the levels of individual, populations and communities in the wild.