Abstract
Climate change has profound impacts on marine biodiversity and biodiversity changes in turn might affect the community sensitivity to impacts of abiotic changes. We used mesocosm experiments and Next Generation Sequencing to study the response of the natural Baltic and Mediterranean unicellular eukaryotic plankton communities (control and +6°C heat shock) to subsequent salinity changes (-5 psu, +5 psu). The impact on Operational Taxonomic Unit (OTU) richness, taxonomic and functional composition and rRNA:rDNA ratios were examined. Our results showed that heat shock leads to lower OTU richness (21% fewer OTUs in the Baltic and 14% fewer in the Mediterranean) and a shift in composition toward pico- and nanophytoplankton and heterotrophic related OTUs. Heat shock also leads to increased rRNA:rDNA ratios for pico- and micrograzers. Less than 18% of shared OTUs were found among the different salinities indicating the crucial role of salinity in shaping communities. The response of rRNA:rDNA ratios varied highly after salinity changes. In both experiments the diversity decrease brought about by heat shock influenced the sensitivity to salinity changes. The heat shock either decreased or increased the sensitivity of the remaining community, depending on whether it removed the more salinity-sensitive or the salinity-tolerant taxa.
Highlights
Multiple components of climate change are projected to affect all levels of biodiversity and ecosystems structure and resilience (Bellard et al, 2012)
In the Mediterranean experiment, Dinophyceae was the taxonomic group with the highest number of Operational Taxonomic Unit (OTU) (403) followed by Fungi (239 OTUs) and Bacillariophyceae (178 OTUs) (Figure 1) and mixotrophs were the trophic group with the highest OTU richness (298) followed by picograzers (270 OTUs) and parasites (212 OTUs) (Supplementary Table 2B)
In this study we examined the influence of biodiversity changes caused by an intermittent heat-shock on the sensitivity of plankton community to subsequent salinity changes
Summary
Multiple components of climate change are projected to affect all levels of biodiversity and ecosystems structure and resilience (Bellard et al, 2012). Based on current knowledge (Intergovernmental Panel on Climate Change [IPCC], 2014), sea surface temperature is predicted to increase up to 3–5◦C by the year 2100 with even stronger increases in semi-enclosed coastal seas. For Thermaikos Bay, Krestenitis et al (2012) found a salinity decrease of almost 1 psu for the period 1994–2007 with a continuous trend. Physical changes like these will lead to changes in community composition, biodiversity and functional attributes which in turn will influence the responsiveness of communities to further physical changes, as has been conceptualized by the doublestressor concept of Vinebrooke et al (2004). The impact of different aspects of climate change on plankton communities has been studied quite extensively (e.g., Yvon-Durocher et al, 2015; Kaur-Kahlon et al, 2016; Moustaka-Gouni et al, 2016), while the effect of plankton community changes on the sensitivity to environmental pressures has not been the focus of experimental studies
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