AME 80:139-152 (2017)  -  DOI: https://doi.org/10.3354/ame01848

ABSTRACT: Ocean acidification will likely have significant impacts on phytoplankton growth in marine ecosystems over the course of this century. Coastal waters, which can be strongly influenced by suspended sediments, can also be particularly sensitive to ocean acidification. While the individual effects of trace metal inputs and ocean acidification have each been well documented, the combined effects of high trace metal concentrations due to mobilization from sediments and high dissolved CO₂ concentrations (low seawater pH) on the growth of marine phytoplankton are not known. In this study, a batch culture experiment was performed using the model organism Cochlodinium polykrikoides over 35 d under a range of CO₂ concentrations (400, 800, and 1200 ppmv) following sediment additions. At high CO₂, dissolved iron (Fe) and nickel (Ni) concentrations increased over time. Dissolved Ni concentrations were significantly higher after 35 d at 1200 ppmv CO₂ compared to the other treatments and corresponded to significant decreases in C. polykrikoides growth rates. In addition, a toxicity bioassay experiment was performed over 29 d under a range of Ni or cadmium (Cd) concentrations at ambient CO₂. The growth responses of C. polykrikoides were dose-dependent and were significantly lower under increasing Ni or Cd concentrations. The findings suggest that a combination of elevated total dissolved Ni supplied from sediments and high CO₂ conditions could suppress the growth rates and photosynthesis of C. polykrikoides in coastal marine ecosystems. This is the first study to examine the synergistic, toxic effects of lithogenic trace metals and CO₂ on phytoplankton growth.

KEY WORDS: Cochlodinium polykrikoides · Sediment · Toxicity · Carbon dioxide · Nickel · Cadmium · Trace metals · Ocean acidification