Wolf, Fabian (2018) The neglected role of environmental fluctuations in climate change research: How temperature variability influences the interaction of macrophytes and their grazers. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 56, II pp.

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Abstract

The projected increase in temperature towards the end of this century in the Baltic Sea is with 4°C higher than the world’s average of 3°C. Furthermore, shifts in temperature variability are additionally likely more pronounced in the Baltic Sea than in the open ocean. Many ecological studies have emphasized the importance of temperature in climate change research. Most conducted experiments, however, did not consider environmental variability. Nevertheless, during temperature peaks, organisms could be stressed even more, compared to mean changes, or temperature minima could act as phases for relaxation. Despite the great relevance, experimental studies on the effect of environmental variability under climate change on communities or ecosystems are almost entirely lacking. This study provides one of the first experiments trying to close this gab of knowledge. Therefore, a three-month long experiment was conducted in the Kiel Indoor Benthocosms, with the key species Fucus vesiculosus and its grazing community Gammarus sp. and Idotea balthica. Applying a seasonal temperature profile as reference treatment, the effects from ambient and future (+ 4°C) temperatures in the Baltic Sea under a constant and fluctuation (± 3°C of the mean) regime were examined. This study showed that F. vesiculosus was disadvantaged by mean warming, especially after the summer maximum temperature (19.7 and 23.7°C in the ambient and future constant temperature regimes). Thus, seasonality impacted the growth of F. vesiculosus, i.e. under ambient constant conditions F. vesiculosus was able to recover from the peak temperature, whereas it was detrimental in all other treatments. The grazer Gammarus sp. was negatively affected by warming, whereas I. balthica benefitted from elevated temperatures. Surprisingly, small-scale fluctuations had little effects on the performance of all three species. However, F. vesiculosus biomass without grazing tended to be positively influenced by fluctuating temperatures under warming, but negatively under ambient conditions. Grazer biomass tended to be negatively affected by fluctuations but seemed to produce larger Gammarus sp. individuals. The experiments showed that not small-scale fluctuations, but rather extremes, e.g. during peak summer temperatures, affected the community very strongly. The foundation species F. vesiculosus as well as Gammarus sp. suffered from the overall warming extremes while I. balthica benefited from these, with likely implication for community structures.

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