Review: Sublethal effects of temperature on freshwater organisms, with special reference to aquatic insects

Abstract

Water temperature is a key variable affecting aquatic organisms. Understanding their response to  elevated water temperatures is important for estimating upper thermal limits, and ultimately for  assisting with setting defendable, biologically-relevant water temperature guidelines for lotic systems.  Sublethal effects impacting on an individual organism or species may manifest at higher levels of the  hierarchy, namely, populations, communities and entire ecosystems. Sublethal effects typically include those affecting an organism’s physiology and metabolism (e.g. growth rates, secondary productivity, respiration); phenology (e.g. development time, voltinism, emergence); reproductive success and  fitness (e.g. fecundity, rates and success of egg development and hatching); behaviour (e.g. migration,  movement, drift); and broad-scale ecological effects (e.g. species richness, composition, density,  distribution patterns). Sublethal effects are discussed with examples drawn from freshwater studies, in particular those focused on aquatic insects.  Commonly-used methods, which vary from simple, cost-effective, laboratory-based methods to more  elaborate, expensive, laboratory- and field-based studies, are assimilated to serve as a toolbox for future  thermal research. Ultimately, the method adopted depends largely on the question(s) being asked and available resources.

Keywords: biotic responses, experimental, riverine ecosystems, thermal research, tolerance