Effects of temperature and chloride salinity on the functional response of goldfish (Carassius auratus)
摘要
Freshwater animals released into temperate urban environments are increasingly subjected to the effects of elevated water temperatures (via climate warming) and salinization (via road salt application). In laboratory experiments, we tested the effects of these stressors on the feeding performance of goldfish (Carassius auratus), a globally invasive species frequently released into urban ponds. Using goldfish from a pet supplier, we measured individual functional response (prey consumption rate as a function of prey density) under combinations of two thermal treatments (18 °C and 26 °C) and two chloride treatments (0 ppt and 0.96 ppt). These treatments represent current and projected surface water temperatures and observed mean chloride contamination, respectively, in ponds in the Montreal (Quebec, Canada) region. Feeding rate was consistently higher at the temperature nearest to the known thermal optimum for goldfish (i.e., 26 °C); this supports the environmental matching hypothesis—which predicts that per capita effects, including foraging efficiency, increase as the ambient temperature approaches thermally optimal conditions. Feeding rate was maximum at the combination of 26 °C and 0 ppt. Therefore, the feeding efficiency (and thus the trophic impact) of goldfish varies with combinations of thermal and salinity conditions typical of urban ponds in north temperate regions, with temperature having a larger influence than salinity over this range. A follow-up study testing feeding efficiency at a realistic lower temperature (10 °C; reflecting spring snowmelt conditions) across three levels of salinity (0 ppt, 1 ppt, and 6 ppt) showed that maximum feeding rate increased with salinity. Therefore, we hypothesize that salinity enhances trophic impacts at temperatures below the thermal optimum.