Award: OCE-1316198

Janet Kübler and Steve Dudgeon and their students performed experiments using artificially mixed atmospheres, temperatures and nutrient additions that mimic scenarios expected to be common as the climate changes. Ocean acidification happens as more carbon dioxide (CO2) dissolves in ocean water. The focus of the work was to assess the impacts of ocean acidification on the algae that are likely to be most positively affected, under the conditions that are mostly likely to stimulate macroalgal blooms. There were three main categories thereof. First, are species that have no mechanisms to take up charged forms of CO2 from the water and may currently have their growth limited by carbon supply. Second, are species that may have energetic savings when the pH is lower and may grow faster at lower pH. Third, species that accumulate under eutrophic conditions that may grow even faster when pH is low and nutrient concentrations are high, as is expected in most coastal waters in the near future. They found that hypothesized positive effects of ocean acidification were often small, and decreased over the duration of longer experiments. Very high carbon dioxide concentrations, expected for the end of the 21st century, were actually detrimental to the growth of seaweeds. At carbon dioxide concentrations expected by the middle of the century, algal growth rates were stimulated directly. Ocean acidification affected growth rates under stress conditions but not when the algae were already growing quickly. In a sense, the added carbon dioxide acted as a supplement to rescue growth under otherwise stressful conditions. That result suggests that ocean acidification may allow macroalgal blooms to initiate and to persist longer than they would if there was not more carbon dioxide dissolved in the ocean. The sea lettuce, Ulva was found to adjust its metabolism to more efficiently take up the abundant carbon dioxide in the water under ocean acidification. Ulva from different locations differed in their responses to ocean acidification. That suggests that some local populations will expand and others will decline as the amount of carbon dioxide dissolved in the ocean increases. Nitrogen and warming had much larger effects on macroalgal growth rates than ocean acidification did. Increasing temperatures and increasing coastal nutrient concentrations are bigger challenges for macroalgal populations than is ocean acidification. But, those challenges will be occurring together as the entire atmosphere and ocean has increasing carbon dioxide concentrations. Overall, coastal conditions expected in the coming few decades, will favor the growth of macroalgae, compared to current conditions. Exactly how much, will depend on complex interactions between many environmental variables. Data from this project are being made available through the Biological and Chemical Oceanography Data Management Office, under project number 2275. The project provided training for two Masters degree graduate students, three undergraduate students and one research technician. Two of three undergraduate students are from background traditionally under-represented in the sciences. One graduate student has matriculated in a doctoral program, the other student is working in the aquarium industry. Impacts of the work beyond publications to the scientific community and student training include K-12 educational outreach in local public schools in the San Fernando Valley and communication with shellfish growers and the seaweed aquaculture industry about ocean acidification and impacts and opportunities with macroalgae in commercial settings. Last Modified: 02/13/2018 Submitted by: Steven R Dudgeon