Effects of warming on the phytoplankton succession and trophic interactions

Lewandowska, Aleksandra M. (2011) Effects of warming on the phytoplankton succession and trophic interactions (Doctoral thesis/PhD), Christian-Albrechts-Universität, Kiel, Germany, 89 pp

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Abstract

There is now a good evidence of ecological impacts of recent climate change on ecosystems worldwide. A major challenge in climate change research on phytoplankton succession is to understand the multiple factors, which drive ecological changes in phytoplankton communities. Increasing sea surface temperature is likely to alter phytoplankton bloom dynamic, phenology and community structure. Recent studies on the global primary production showed decline in size and productivity of marine phytoplankton in relation to climate warming. Reorganisation of phytoplankton community with warming can change community interactions and energy flow through
the whole marine food web. The aim of this study was to examine the impact of light and temperature on the
spring phytoplankton bloom and disentangle direct and indirect effects of warming on phytoplankton. I conducted two indoor mesocosm experiments with the natural winter plankton community from the Kiel Bay, Baltic Sea. In the first experiment the combined effects of the factors light and temperature were tested and in the second experiment the factors temperature and zooplankton density were crossed. Additionally, I also included the data from four earlier experiments performed with the same experimental system in a metaanalysis on the effects of warming on primary productivity and an analysis of the pathways between temperature, diversity and productivity of phytoplankton.
In the first chapter of this thesis, I described the results of performed metaanalysis and presented the interactions between temperature, phytoplankton diversity and primary productivity. This analysis allowed me to expand an earlier experimental work on the overall effects of warming on phytoplankton succession. I found a general direct positive temperature effect on the specific primary productivity and an independent positive effect of phytoplankton species richness on the net and specific primary productivity.
I concluded, that there are other factors than temperature (e.g. grazing, nutrient limitation), which might affect phytoplankton diversity and change diversity-productivity
relationship. My experimental work, presented in chapters 2 and 3, focused on combined light and temperature or consumer density and temperature impacts on the phytoplankton succession. Overall, the phytoplankton bloom started earlier in warmer conditions. Surprisingly, light intensity within the range studied (32 to 64% of sea surface irradiance on cloudless days) had only a weak effect on phytoplankton bloom phenology and
community composition, whereas the temperature effects were stronger. In general, I observed a decline of phytoplankton standing biomass and a decline in phytoplankton size with warming, which effects were related to increased grazing pressure under higher temperature. Higher consumer activity changed community composition and dominance of phytoplankton species and increased phytoplankton diversity (richness and evenness). In the chapter 3, I show that warming can shift community composition of copepods, the main phytoplankton grazers. Furthermore, the identity of copepods could be meaningful for changes in phytoplankton diversity. Thus, I suggested that the species specific interactions might be crucial to understand changes in phytoplankton community in response to climate warming.
To summarize my experimental studies and data analyses, I developed a conceptual model of temperature impacts on biotic interactions in marine plankton. In this model temperature can directly act on specific primary productivity and indirectly (via consumers) affect phytoplankton biomass and diversity. I concluded that the primary productivity in marine pelagic ecosystem depends on the relative strength between direct and indirect temperature effects and on the consumer-producer interactions. My work, described in this thesis, highlights the importance of the complex studies on phytoplankton community for understanding ecological processes in aquatic ecosystems and their response to predicted climate warming. This complexity might be achieved by combining field work with experimental studies and testing multiple factors, which affect phytoplankton community.

Document Type: Thesis (Doctoral thesis/PhD)
Thesis Advisors: UNSPECIFIED
Keywords: Food Webs; Ecology; AQUASHIFT; phytoplankton
Research affiliation: OceanRep > GEOMAR > FB3 Marine Ecology > FB3-EOE-N Experimental Ecology - Food Webs
Date Deposited: 19 May 2011 11:41
Last Modified: 13 Dec 2013 11:30
URI: http://eprints.uni-kiel.de/id/eprint/11862

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