Individual performance niches may buffer population responses to climate change in estuarine fishes

Abstract

AbstractClimate change may impact individual organisms in different ways, a consideration often overshadowed by predominant focus on population effects in studies. We examined three estuarine fish species to determine if individual fish performance, persisted across winter water temperatures. Fish performance at 16°C (current Sydney winter estuarine water temperature) and 20°C (predicted under climate change) with low and high food regimes was assessed using key physiological (growth, aerobic scope, burst speed) and behavioural parameters (foraging activity, boldness, shelter usage, predator escape response). We expected a strong positive relationship between performance at 16°C and 20°C for each parameter, and interactions with food level, however in general this was not found for any species. Relative performance was only maintained across temperatures for a few parameters, such as bite rate, boldness, and shelter response in one species (trumpeterPelates sexlineatus), with aerobic scope in silver biddyGerres subfasciatus, and boldness in fortescueCentropogon australis.Our results suggest that individuals’ fitness (directly via changes in growth, indirectly via behaviours) will be impacted by climate warming due to differences in relative performance among individuals across water temperatures. Changes in relative performance among individuals may initially compensate for a population-level response, thereby buffering the effects of climate change.