AME prepress abstract  -  DOI: https://doi.org/10.3354/ame01868

Shifts in phytoplankton community structure modify bacterial production, abundance, and community composition

Maria T. Camarena-Gómez*, Tobias Lipsewers, Jonna Piiparinen, Eeva Eronen-Rasimus, Daniel Perez-Quemaliños, Laura Hoikkala, Cristina Sobrino, Kristian Spilling

*Email: maria.camarena@environment.fi

ABSTRACT: In recent decades, the phytoplankton community has shifted from diatom dominance to co-occurrence of diatoms and dinoflagellates during the spring bloom in parts of the Baltic Sea. We investigated whether this shift affects bacterial production (BP), abundance, and community composition (BCC). Two mesocosm experiments were carried out with water from the SW coast of Finland during the winters of 2012 and 2013. The water was collected before the onset of the spring bloom. Natural seawater was used as a control, and various inocula of diatom and dinoflagellate cultures were used as treatments. After the phytoplankton bloom development, BP (thymidine-BPT and leucine-BPL) was significantly higher in the diatom treatments than in the controls and dinoflagellate treatments (BPT-L in 2012 and BPL in 2013). In 2013, the BCC was significantly different between the diatom and dinoflagellate treatments and there was a temporal shift in both experiments. Alphaproteobacteria predominated in all the treatments at the beginning of the experiments and shifted to flavobacterial (2012) and betaproteobacterial predominance (2013) during the chlorophyll a peak. Towards the end of the experiment, Actinobacteria and Betaproteobacteria predominated in the diatom treatment in 2012, whereas in 2013 Flavobacteriia (all treatments) predominated together with Gammaproteobacteria and Cytophagia (diatom treatments). The results demonstrated that bacterial physiology and community structure are affected by relatively small changes in the phytoplankton community. Thus, the ongoing changes in the phytoplankton community resulting from co-occurrence of diatoms and dinoflagellates may decrease pelagic remineralization of carbon and reduce organic matter fluxes through the microbial loop.