Grosser, Katharina (2008) Der Einfluss von Lichtfluaktionen auf Makroalgen. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 94 pp.

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Abstract

Phototrophic aquatic organisms like macroalgae depend on a certain quantity and quality of light. Changes in intensity and spectral composition of light by entering the water and during the passage of light through the water column are of major importance to these organisms. So a prerequisite for understanding the marine ecosystem is knowledge about light stress, induced by high light intensity, occurring especially near the surface, and low light intensity increasing with depth. Scattering and refraction of light at the wavy water surface create a highly dynamic light regime with various light intensities of different periods in the watercolumn. Only little research on the impact of this light fluctuation with regard to marine macroalgae was done till now and this research concentrated on photosynthesis and growth. A positive effect of light fluctuation on photosynthetic rate of different macroalgae at high mean light intensities with high frequencies was found in these studies. But what is the effect of light fluctuation on algae growing under light stress induced by low light intensities, when light fluctuations might be the only source to enough light energy for the assembly of organic matter? How does the fluctuation impact the condition of the algae, particularly on the interaction with other organisms like bacteria or herbivores? This thesis tries to elucidate the impact of light fluctuation on Fucus vesiculosus and organisms interacting with it at a mean light intensity near the light compensation point of Fucus. Individual Fucus were treated with fluctuating and constant light, and growth as well as photosynthesis was determined. Furthermore the influence of fluctuation on the interaction of Fucus with associated bacteria and its predator Idotea baltica was analysed. The Results show an impact of light fluctuation at low light intensities at the light compensation point on the macroalgae. This was not found in photosynthesis or growth of F. vesiculosus but in the feeding defence to Idotea and in the bacterial fouling on the thalli surface. The effect of fluctuation on feeding defences was clearly negative. Algae grown under fluctuating light were preferred in feeding experiments compared to algae grown under constant. Different light regimes were simulated with a DLP projector. In general it was possible to create a sufficient light regime with this method while at the same time excluding factors like mechanical stress through waves. Some problems occurred, as in longer experimental runs mean light varied, showing that this method needs some refinement, e.g. by using other lamps. If and how the results found here can be translated to natural conditions, were many other factors complicate the situation, remains unanswered, so that this question should be addressed by outdoor test.

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