ten Brink, Felicitas (2019) Effects of heat stress on the feeding behaviour of the marine grazer Paracentrotus lividus. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 74 pp.

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Abstract

Rising temperatures remain one of the principal stressors influencing ecological interactions in the ocean by changing the metabolic functions of marine species. Herbivory is a key factor in regulating plant biomass and the fact that temperature affects different species with varying strength can potentially change plant-herbivore relationships. In the experiments presented in this master thesis, the effects of short term heat stress on the diet composition and the feeding behaviour of the common herbivore sea urchin Paracentrotus lividus were investigated. The experiment was conducted in two parts, the first part being a no-choice feeding assay with only one species of algae offered per sea urchin and the second part being a choice feeding assay with an assemblage of five different algae offered simultaneously. Three hypotheses were tested: 1. Consumption rates change with temperature, 2. P.lividus exhibits a feeding preference and 3. Feeding preference changes with temperature. The organisms were exposed for 10 days to the five elevated temperature treatments, which were 23°C, 25°C, 26°C, 27°C and 29°C. Then the feeding assays with live algae were conducted and consumption rates were calculated. Analysis of variance (ANOVA) was performed as a statistical tool to detect significant differences between treatments. Surprisingly, I found that short term heat stress has only small effects on feeding rates and does not lead to a change in food preference. The sea urchin showed a preference for the algae Ulva compressa. Temperature-driven and non-selective increase of consumption by the grazer might override any physiological effects of temperature on the alga. This can potentially increase top-down grazing pressure. However, as the increase of consumption was small, the ecological effect might be unimportant for this study system and ecosystem changes are rather driven by direct temperature effects than by a change in species interaction.

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