Schaub, Iris (2012) Der wechselseitige Einfluss von Ozeanversauerung und Nahrungsbedingungen auf die Seepocke Amphibalanus improvisus. (Diploma thesis), Universität Rostock, Rostock, Germany, .99 pp.

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Abstract

Due to a steady increase of carbon dioxide concentrations in the atmosphere, the oceans take up more CO2 causing an increase in seawater pC02 and a decrease in seawater pH and calcite saturation state. Already today, especially in the late summer and autumn, low pHvalues can occur in the surface water of the Kiel Fjord due to the upwelling of CO2 rich bottom water. This is mainly caused by the degradation of phytoplankton blooms additionally increased by eutrophication of the oceans. Assuming that organisms from fluctuating habitats with respect to pCO2 and pH are adapted to - or at least able to cope with these conditions, their tolerance might be reduced when food - and thus energy - is limited. In the present study, freshly settled juvenile barnacles of the species Amphibalanus improvisus were reared for 5 months under experimental conditions. The combined effects of three pCOr (3 80, 1120 and 4000 ppm) and two feeding levels (high and low; 5: 1) on growth, reproduction and calcification, as well as the effects of the pCO2 stress on the settlement success of the offspring generation of the reared barnacles were investigated. Growth and reproduction were not affected by an increase of seawater pCO2, regardless of the diet. In the 4000 μatm pCO2 treatment with seawater undersaturated with respect to calcite, the external organic layer of the barnacle shell (epicuticle) peeled off under the long term exposure to the corrosive water with the underlying calcium carbonate layer starting to dissolve. Barnacles increased the calcification to compensate increasing CaCO3 dissolution. Since energy for successful compensatory calcification was possibly limited in the low food treatment, a decrease in shell strength was observed under the 4000 μatm pCO2 treatment. This reduction in shell strength could lead to an increased susceptibility of barnacles to crushing and drilling predators. The applied pCO2 and food treatments had furthermore no significant effects on the development and the settlement success of the offspring barnacle larvae. These results show that the barnacle Amphibalanus improvisus can cope with predicted future ocean acidification even under limited food conditions. A decrease in shell strength and thus a possible increase in susceptibility of barnacles towards their predators could nevertheless have negative effects on barnacle populations in the future. This highlights on the importance to investigate species interactions in response to multiple environmental stressors such as pC02 and food limitation.

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