Hennigs, Laura M. (2017) The Effect of Fluctuating pCO2 Concentrations on the Growth of the Barnacle Balanus improvisus in Different Temperatures. (Bachelor thesis), Universität Oldenburg, Oldenburg, Germany, 63 pp.

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Abstract

In times of global change, pH fluctuations induced by 0macrophytes due to their biological activity are discussed to have the potential of offering refuge from acidification stress by elevating the pH at daytime. These fluctuations are extremely high in the diffusive boundary layer (DBL) of macrophytes, but also in the greater surroundings of dense macrophyte beds. In the present study, the effects of warming, ocean acidification and two types of pH fluctuations on the survival and growth of the barnacle B. improvisus on two different substrates, Plexiglas and Fucus serratus, were examined. In a five week laboratory experiment, early juvenile B. improvisus from the Western Baltic were kept in different treatments in water flow-through systems. A fully crossed design with the factors 'temperature' (10, 15 °C), 'mean pH' (7.8, 8.1), 'fluctuation type' (constant, fluctuating) and 'substrate' (Plexiglas, Fucus) was used. Warming positively affected the survival of B. improvisus on Fucus, but only under ambient pH conditions. Growth of B. improvisus was significantly increased by warming in almost all factor combinations. Neither acidification, nor pH fluctuations which simulated those induced by a nearby macrophyte bed, showed significant effects on barnacles' survival and growth. Comparing the substrates, survival and growth of B. improvisus were significantly larger on Plexiglas and not, as expected, on Fucus. Thus, pH fluctuations induced by the DBL of Fucus significantly affected the response negatively, even under ocean acidification. The conclusions of this study are, that (1) warming in spring acts as a boosting factor for barnacles' performance, (2) B. improvisus from Kiel Fjord shows a high tolerance towards ocean acidification, regardless of its life-stage, (3) pH fluctuations simulating those induced by a macrophyte bed do not affect barnacles' performance and that (4) pH fluctuations induced by the DBL - or other characteristics of Fucus - hamper barnacles' performance.

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