Background
The authors write that "although seagrasses and marine macroalgae (macro-autotrophs) play critical ecological roles in reef, lagoon, coastal and open-water ecosystems, their response to ocean acidification (OA) and climate change is not well understood," and, therefore, they proceed to review the scientific literature as it pertains to these subjects in these two groups of aquatic plants.

What was done
Koch et al. say they examined "marine macro-autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon (DIC), carbon dioxide (CO2), and lower carbonate (CO3^2-) and pH," while also exploring "the effects of increasing temperature under climate change and the interactions of elevated temperature and CO2."

What was learned
The four researchers determined that their "literature review of >100 species revealed that marine macro-autotroph photosynthesis is overwhelmingly C3 (>=85%) with most species capable of utilizing HCO3^-," and that "most are not saturated at current ocean DIC," which results lead them to conclude that "photosynthetic and growth rates of marine macro-autotrophs are likely to increase under elevated CO2 similar to terrestrial C3 species."

What it means
Noting that "the photosynthesis of the majority of the species examined was not saturated at the current levels of DIC in the ocean and responded to an increase in CO2," Koch et al. conclude that seagrasses and many marine macroalgae have the potential to respond positively, in terms of photosynthesis and growth, under elevated ocean CO2 and OA.