EFFECTS OF OCEAN ACIDIFICATION ON ANTARCTICA MICROBIAL COMMUNITIES

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RESEARCH PROJECT TOPIC ON EFFECTS OF OCEAN ACIDIFICATION ON ANTARCTICA MICROBIAL COMMUNITIES

Abstract
The ocean absorbs about 25-30% of the anthropogenic CO2 emissions which has already
lowered the pH in the oceans by 0.1 units compared to preindustrial levels. Given that the
CO2 in the atmosphere reaches 1000 ppm in year 2100, the ocean pH is predicted to decrease
by 0.4 pH units during the coming 90 years. This ocean acidification (OA) is expected to have
impacts on processes such as nitrogen and carbon cycling. Bacteria are of great importance
for these processes, and effects on the structure and activity of bacterial communities could
potentially alter the availability of nitrogen and carbon for other organisms and affect the
entire food web. OA is predicted to make certain metals and antibiotics more bioavailable,
which would create a stronger selection pressure for resistance. The aim of the project was to
investigate the response of bacterial communities to ocean acidification in a mesocosm study.
Ten mesocosms were placed in the Gullmar Fjord; five were treated with 1000 µatm CO2
(high) and five were left untreated (control). Samples were collected once a week during the
period 8th of March to 15th of May. The responses investigated were: changes in bacterial
community composition by PCR-DGGE, enumeration of total bacterial abundance by
epifluorescence microscopy of DAPI-stained bacteria, and the prevalence of copper and
antibiotic resistance by spreading water on agar plates containing copper or antibiotics. The
results showed a change in community composition at the peak of the first phytoplankton
bloom and at the decline of the second phytoplankton bloom, although the species richness
remained the same. Effects of OA on the community composition have been found in
previous mesocosm and microcosm studies and have been proposed to influence the carbon
pump in the ocean. There was a decrease in bacterial abundance in the high CO2 mesocosms
at the peak of the second spring bloom. No effect of OA could be seen for the prevalence of
antibiotic or copper resistance. Which species or functional groups of bacteria shifted in the
community composition were not investigated during this project. In future studies, this
would be interesting to investigate in order to assess which effect the change in community
composition might have on the pelagic ecosystem

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