Direct and indirect climatic drivers of biotic interactions: ice-cover and carbon runoff shaping Arctic char Salvelinus alpinus and brown trout Salmo trutta competitive asymmetries

Abstract

One of the major challenges in ecological climate change impact science is to untangle the climatic effects on biological interactions and indirect cascading effects through different ecosystems. Here, we test for direct and indirect climatic drivers on competitive impact of Arctic char (Salvelinus alpinus L.) on brown trout (Salmo trutta L.) along a climate gradient in central Scandinavia, spanning from coastal to high-alpine environments. As a measure of competitive impact, trout food consumption was measured using (137)Cs tracer methodology both during the ice-covered and ice-free periods, and contrasted between lakes with or without char coexistence along the climate gradient. Variation in food consumption between lakes was best described by a linear mixed effect model including a three-way interaction between the presence/absence of Arctic char, season and Secchi depth. The latter is proxy for terrestrial dissolved organic carbon run-off, strongly governed by climatic properties of the catchment. The presence of Arctic char had a negative impact on trout food consumption. However, this effect was stronger during ice-cover and in lakes receiving high carbon load from the catchment, whereas no effect of water temperature was evident. In conclusion, the length of the ice-covered period and the export of allochthonous material from the catchment are likely major, but contrasting, climatic drivers of the competitive interaction between two freshwater lake top predators. While future climatic scenarios predict shorter ice-cover duration, they also predict increased carbon run-off. The present study therefore emphasizes the complexity of cascading ecosystem effects in future effects of climate change on freshwater ecosystems.

Arctic charr (Salvelinus alpinus) squeezed in a complex fish community dominated by perch (Perca fluviatilis)

“…However, the species seems to select a lower temperature than what is optimal for its growth, probably because it is optimizing its growth efficiency instead of its growth rate (Berglund 2005), and this may explain the low annual growth rate of charr in Lake Skasen. The growth efficiency at low temperatures is likely the basis for the improved competitive abilities of Arctic charr in colder waters and during periods with ice cover , Helland et al 2011, Ulvan et al 2011.…”

“…The natural distribution of Arctic charr in Norway is mainly in lowland lakes along the coast, but also in inland lakes in the middle and northern part of the country (Huitfeldt-Kaas 1918;Hesthagen & Sandlund 1995). Indications are that climate warming, in general resulting in higher water temperatures, may put Arctic charr at a disadvantage relative to sympatric fish species , Ulvan et al 2011. The Arctic charr populations in lowland South Eastern Norway and southern Sweden are on the margin of the species' distribution in Scandinavia, and in many cases serious population decline and even local extinctions have been reported (Dickson 1975;Nysaether 1977;Sandlund et al 2010).…”

Seasonal and ontogenetic shifts in the diet of Arctic charr Salvelinus alpinus in a subarctic lake

“…, Ulvan et al 2012), more research is still needed to predict and assess the potential impacts of climate warming on fish communities and, in particular, on food-web dynamics in subarctic lakes (Jeppesen et al 2010, Hein et al 2012.…”

“…Consequently, Arctic charr have probably outcompeted brown trout from the most unproductive highaltitude lakes . Despite increasing knowledge about competitive interactions between Arctic charr and brown trout , Ulvan et al 2012), more research is still needed to predict and assess the potential impacts of climate warming on fish communities and, in particular, on food-web dynamics in subarctic lakes (Jeppesen et al 2010, Hein et al 2012.…”

“…Similarly, introduction of whitefish (Coregonus lavaretus (L.)) and natural spread of pike (Esox lucius L.) have had detrimental consequences for native Arctic charr populations in 15 northern Fennoscandia , Byström et al 2007). Potential future changes in ice-cover period and water colour may also have significant but complex impacts on the competitive interactions between Arctic charr and brown trout (Salmo trutta L.) , Ulvan et al 2012. Hence, understanding how Arctic charr and its sympatric resource competitors partition food and habitat resources is crucial for monitoring and managing subarctic lakes and their fish communities (Jeppesen et al 2010, Hein et al 2012.…”