The effect of climate change on Galaxias maculatus thermal habitat availability in northern Andean Patagonian lakes

Abstract

Temperature is a prime driver of biological systems, and has implications for populations, community dynamics and stability across entire lake food webs. Galaxias maculatus is a keystone prey species in Patagonian lakes due to its trophic and habitat coupling roles. Adverse effects on this species could cascade through food webs, threatening the biotic integrity of Patagonian lakes. Our aim was to define the current use of available thermal habitats by three G. maculatus life stages in three morphologically dissimilar lakes of the Andean range and to simulate potential shifts in thermal habitat availability. Thermal habitat availability simulations derived for the 4.5- and 8.5-W/m2 radiative forcing values of greenhouse gas Representative Concentration Pathway scenarios up to 2099 were run for the three lakes. The availability of simulated thermal habitats for 2099 was used to analyse possible consequences for G. maculatus, using thermal habitat suitability index curves. The curves were defined from the temperature dependence of the maximum consumption of each life stage of G. maculatus considered. Our results showed that thermoclines would form at greater depths in the two deep lakes and remain stable for longer periods than at present. For the shallow lake, which does not currently form a thermocline, Representative Concentration Pathway scenarios predict higher water temperatures and absence of winter freezing. Galaxias maculatus currently encounters better thermal habitat for food consumption in the shallow than the deep lakes. Simulations for the deep lakes indicated that future climate change will not be detrimental to any G. maculatus life stage. However, in shallow lakes its earlier life stages will encounter lower quality thermal conditions. Lower quality thermal conditions in shallow lakes could result in a reduction in G. maculatus numbers, which could affect entire food webs given that this species is a keystone prey species. In turn, this could threaten the biotic integrity of these lakes. Our results raise the question: what happens in other lakes around the world that have low food web complexity, dynamic processes, and structure, which depend on a single vulnerable keystone prey species? The lack of research addressing the role of keystone species in relation to global climate change suggests that this question has not been thoroughly addressed and requires further study around the world.