Resource use and consumption of three-spined sticklebacks (Gasterosteus aculeatus) under different environmental conditions during winter.

Abstract:

In temperate climate with pronounced seasonality, ice and snow cover reduces light conditions during winter which in turn reduce search efficiency for visual feeding consumers like fish. Furthermore, a suggested major effect of future climate change is an increased input of allochtonous DOC to aquatic systems which causes an increased brownification and hence reduced overall light conditions. In this study, I sampled YOY three-spined sticklebacks (Gasterosteus aculeatus) of different sizes overwintering in clear and brown water model ecosystems to examine if consumption were dependent on light conditions (natural light variability over winter) and if consumption were reduced in brown water. Three-spined sticklebacks were able to feed at different winter conditions and the prey biomass in stomachs was higher in clear- than in brown water despite higher resource levels in brown water treatments. Moreover when light intensity increased in late winter compared to midwinter conditions prey biomass in stomachs increased in both clear and brown water systems. Dominated prey taxa in the diet were chironomids and copepods. Results from this study suggest that when fish species are able to feed at low temperature and resource availability are sufficient light conditions during winter can be an important factor affecting overwinter survival in YOY fish because visual prey encounters and hence consumption rates are affected by light conditions. Future climate change scenarios with predicted increased brownification may therefore affect over winter survival in fish because of the negative effect of low light intensity (brownification) on prey consumption in fish in turn potentially changing recruitment success and densities of fish.