Temperature and resource availability may interactively affect over-wintering success of juvenile fish in a changing climate

Abstract

The predicted global warming may affect freshwater systems at several organizational levels, from organism to ecosystem. Specifically, in temperate regions, the projected increase of winter temperatures may have important effects on the over-winter biology of a range of organisms and especially for fish and other ectothermic animals. However, temperature effects on organisms may be directed strongly by resource availability. Here, we investigated whether over-winter loss of biomass and lipid content of juvenile roach (Rutilus rutilus) was affected by the physiologically relatively small (2-5 °C) changes of winter temperatures predicted by the Intergovernmental Panel on Climate Change (IPCC), under both natural and experimental conditions. This was investigated in combination with the effects of food availability. Finally, we explored the potential for a correlation between lake temperature and resource levels for planktivorous fish, i.e., zooplankton biomass, during five consecutive winters in a south Swedish lake. We show that small increases in temperature (+2 °C) affected fish biomass loss in both presence and absence of food, but negatively and positively respectively. Temperature alone explained only a minor part of the variation when food availability was not taken into account. In contrast to other studies, lipid analyses of experimental fish suggest that critical somatic condition rather than critical lipid content determined starvation induced mortality. Our results illustrate the importance of considering not only changes in temperature when predicting organism response to climate change but also food-web interactions, such as resource availability and predation. However, as exemplified by our finding that zooplankton over-winter biomass in the lake was not related to over-winter temperature, this may not be a straightforward task.

Figure 1. Standardized development of condition (K) for unfed (top panel) and fed fish (lower panel) at three different experimental temperatures.

Values at day 0 are based on fish caught in the field and data for field caught fish at day 98 are indicated by arrows. Punctured horizontal lines indicate average (± S.E.) standardized dry-weight condition of fish that died during the experiment. Error bars indicate S.E. and bold error bars indicate S.E. for fish caught in the field at day 0 and day 98.

Figure 2. Average rate of change, calculated from regression coefficients, in relative body condition (δK day⁻¹) for fed (filled circles) and unfed fish (open circles) at three different experimental temperatures.

Filled square indicate fish in Lake Krankesjön, where the average winter temperature during the study period was 2.51°C and shaded area indicate the potential range for rate of change at different temperatures dependent on food supply. Error bars indicate standard error on regression coefficients.

Figure 3. Standardized development of lipid content for unfed (top panel) and fed fish (lower panel) at three different experimental temperatures.

Values at day 0 are based on fish caught in the field and data for field caught fish at day 98 is indicated by arrows. The average proportional lipid content of fish caught on day 0 was 0.1435. All lipid contents are given as deviations from this value. Punctured horizontal lines indicate average (± S.E.) standardized lipid content of fish that died during the experiment. Error bars indicate S.E. and bold error bars indicate S.E. for fish caught in the field at day 0 and day 98.

Figure 4. Seasonal development of (A) winter temperatures (°C) and (B) Ln zooplankton biomass (µgl⁻¹) in Lake Krankesjön during five consecutive winters.

Fat line in both figures refers to predicted values from quadratic polynomial regression analysis.