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Aquatic Microbial Ecology

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AME 51:105-115 (2008)  -  DOI:

Climate warming in winter affects the coupling between phytoplankton and bacteria during the spring bloom: a mesocosm study

Hans-Georg Hoppe1,*, Petra Breithaupt1, Katja Walther2, Regine Koppe1, Stephan Bleck1, Ulrich Sommer1, Klaus Jürgens2

1Leibniz Institute of Marine Science, IfM-GEOMAR, Düsternbrooker Weg 20, 24105 Kiel, Germany
2Leibniz Institute of Baltic Sea Research (IOW), Seestrasse 15, 18119 Rostock, Germany

ABSTRACT: The response of the phytoplankton and bacterial spring succession to the predicted warming of sea surface temperature in temperate climate zones during winter was studied using an indoor-mesocosm approach. The mesocosms were filled with winter water from the Kiel Fjord, Baltic Sea. Two of them were started at ~2°C and the temperature was subsequently increased according to the decadal temperature profile of the fjord (ΔT 0°C, baseline treatment). The other mesocosms were run at 3 elevated temperatures with differences of ΔT +2, +4 and +6°C. All mesocosms were exposed to the same light conditions. Timing of peak phytoplankton primary production (PP) during the experimental spring bloom was not significantly influenced by increasing temperatures, whereas the peak of bacterial secondary production (BSP) was accelerated by about 2 d per °C. This suggests that, in case of warming, the spring peak of bacterial degradation of organic matter (in terms of BSP) would occur earlier in the year. Furthermore, the lag time between the peaks of PP and BSP (about 16 d for ΔT 0°C) would diminish progressively at elevated temperatures. The average ratio between BSP and PP increased significantly from 0.37 in the coldest mesocosms to 0.63 in the warmest ones. Community respiration and the contribution of picoplankton (<3 µm fraction) to this also increased at elevated temperatures. Our results lead to the prediction that climate warming during the winter/ early spring in temperate climate zones will favor bacterial degradation of organic matter by tightening the coupling between phytoplankton and bacteria. However, if PP is reduced by warming, as in our experiments, this will not necessarily lead to increased recycling of organic matter (and CO2).

KEY WORDS: Bacterial secondary production · Baltic Sea · Climate change · Global warming · Marine bacteria · Mesocosm · Primary production · Respiration

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Cite this article as: Hoppe HG, Breithaupt P, Walther K, Koppe R, Bleck S, Sommer U, Jürgens K (2008) Climate warming in winter affects the coupling between phytoplankton and bacteria during the spring bloom: a mesocosm study. Aquat Microb Ecol 51:105-115.

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