Abstract
Abstract. Diatoms account for up to 50 % of marine primary production and are considered to be key players in the biological carbon pump. Ocean acidification (OA) is expected to affect diatoms primarily by changing the availability of CO2 as a substrate for photosynthesis or through altered ecological interactions within the marine food web. Yet, there is little consensus how entire diatom communities will respond to increasing CO2. To address this question, we synthesized the literature from over a decade of OA-experiments with natural diatom communities to uncover the following: (1) if and how bulk diatom communities respond to elevated CO2 with respect to abundance or biomass and (2) if shifts within the diatom communities could be expected and how they are expressed with respect to taxonomic affiliation and size structure. We found that bulk diatom communities responded to high CO2 in ∼60 % of the experiments and in this case more often positively (56 %) than negatively (32 %) (12 % did not report the direction of change). Shifts among different diatom species were observed in 65 % of the experiments. Our synthesis supports the hypothesis that high CO2 particularly favours larger species as 12 out of 13 experiments which investigated cell size found a shift towards larger species. Unravelling winners and losers with respect to taxonomic affiliation was difficult due to a limited database. The OA-induced changes in diatom competitiveness and assemblage structure may alter key ecosystem services due to the pivotal role diatoms play in trophic transfer and biogeochemical cycles.
Highlights
The global net primary production (NPP) of all terrestrial and marine autotrophs amounts to approximately 105 petagrams (Pg) of carbon per year (Field et al, 1998)
We explored the response of diatom assemblages to high CO2 by searching the literature for relevant results with Google Scholar (15 December 2017) using the following search query: “diatom” OR “Bacillariophyceae” AND “ocean acidification” OR “high CO2” or “carbon dioxide” OR “elevated CO2” OR “elevated carbon dioxide” OR “low pH” OR “decreased pH”
We found 54 relevant publications on CO2 experiments with natural diatom assemblages
Summary
The global net primary production (NPP) of all terrestrial and marine autotrophs amounts to approximately 105 petagrams (Pg) of carbon per year (Field et al, 1998). A taxonomically diverse group of cosmopolitan phytoplankton, were estimated to contribute up to 25 % (26 Pg C yr−1) to this number, which is more than the annual primary production in any biome on land (Field et al, 1998; Nelson et al, 1995; Tréguer and De La Rocha, 2013). Since the formation of this shell requires dissolved silicate, diatoms are often limited by silicon as a nutrient rather than by nitrogen or phosphate (Brzezinski and Nelson, 1996). When dissolved silicate is available, diatoms benefit from their high nutrient uptake and growth rates, allowing them to outcompete other phytoplankton and form intense blooms in many ocean regions (Sarthou et al, 2005)
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