Ocean Acidification Increases the Accumulation of Toxic Phenolic Compounds Across Trophic Levels

Prof. Kunshan Gao (from State Key Laboratory of Marine Environmental Science, Xiamen University) and other professors collaboratively published "Ocean Acidification Increases the Accumulation of Toxic Phenolic Compounds Across Trophic Levels" inNature Communications in October, 2015.

Increasing atmospheric CO₂ concentration is causing ocean acidification (OA), altering carbonate chemistry with consequences for marine organisms. The article shows that OA increases by 46-212% the production of phenolic compounds in phytoplankton grown under the elevated CO₂ concentration projected for the end of this century, compared with the ambientCO₂ level. At the same time, mitochondrial respiration rate is enhancedby 130-160% under the elevatedCO₂ concentrations in a single species or mixed phytoplankton assemblage. When fed with phytoplankton cells grown under OA, zooplankton assemblages have significantly higher phenolic compound content, by about 28-48%. The functional consequences of the increased accumulation of toxic phenolic compounds in primary and secondary producers have the potential to cause profound influence to marine ecosystem and seafood quality, with the possibility that fishery industry could be influenced as a result of progressive ocean changes.

To address this issue, researchers here employ a proteomics approach to investigate the responses of a coccolithophorid, Emiliania huxleyi (CCMP 1516), to elevate CO₂ at the molecular level. On the basis of the proteomics study findings, they hypothesize that OA could enhance some metabolic pathways, leading to increasing production of phenolic compounds. To prove this, they measured the levels of phenolic compounds and mitochondrial respiration rates of phytoplankton in monospecific laboratory cultures and in mixed phytoplankton assemblages, which were grown under different levels ofCO₂. Subsequently, zooplankton assemblages were fed with phytoplankton cells grown under the elevatedCO₂ concentration to examine possible food chain effects. The results show that OA increases the levels of phenolic compounds in phytoplankton by enhancing β-oxidation, Krebs cycle and mitochondrial respiration, and the accumulated phenolic compounds are transferred to higher trophic levels (zooplankton).