Beck, Miriam (2017) Grazing of amphipod Gammarus sp. on macroalgae Fucus vesiculosus under climate change: a mesocosm experiment. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 35 pp.

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Abstract

The ongoing temperature increase due to climate change will affect the behaviour and interaction of marine organisms and might lead to stress conditions. According to previous studies, the grazing rates by meso-grazers will increase due to increased metabolism rates under warmer conditions until a threshold, above which negative stress effects occur. In macroalgae it has been observed that heat stress above this temperature reduces growth as well as anti-grazing defences. This suggests that under future climate conditions the grazing pressure on macroalgae will increase. I conducted monthly grazing experiments over a period of five months to investigate grazing rates of the meso-grazer amphipod Gammarus sp. on macroalgae Fucus vesiculosus using a temperature increase based on IPCC [2013] projections. A fully crossed design with both organisms previously being exposed to either ambient temperature or Δ+4°C for several months or collected directly from the field, should help to disentangle the possible reasons for the expected variation in grazing rates. I did not find an effect of temperature treatment on grazing rates to any time in any experiment. However, there was the trend of slightly higher grazing rates under warm conditions, and grazing rates increased with season and temperature. The effect of seasonality on occurrence for grazing was significant and it increased with time. The main reason for these findings might be the expected increased metabolism of grazers. However, also presence of predators and temperature events (heat wave, cold period) might explain some observed patterns. Gammarus sp. seem to acclimatize to elevated temperatures, as they showed a lower response to seasonal increasing temperature than grazers that were not exposed to elevated temperature before. Generally, pre-treated F. vesiculosus was more prone to grazing which suggests that it will experience negative stress effects (temperature, increased grazing pressure) under future conditions.

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