Ocean Acidification Differentially Affects the Photosynthesis of Key New England Macrophytes
Abstract
While the influence of anthropogenic CO2 emissions on seawater chemistry is detrimental to calcification among CaCO3 reliant organisms such as commercially important shellfish species, non-calcareous macrophytes like seagrasses and seaweeds can experience enhanced growth under elevated pCO2 conditions and may be a substantial, if ephemeral, CO2 sink. Most marine macrophytes rely on enzyme conversion of HCO3- to supply the inorganic carbon necessary for photosynthesis; the ability to down-regulate this energetically expensive carbon acquisition under high pCO2 conditions could determine future species success. We exposed four commercially and ecologically relevant New England macrophytes (Saccharina latissima, Fucus vesiculosus, Ulva lactuca, and Zostera marina) to pre-industrial (280 uatm), present (400 and 520 utam - recorded in Casco Bay) and future (640, 880 and 1120 uatm - as predicted by the IPCC) pCO2 levels in 1.5 hr long respirometry assays after 72 hrs acclimation. CO2 consumption, photosynthetic quotient (Q = CO2 consumed:O2 evolved), and change in carbonate saturation state (Ωcalcite) were calculated for each sample using differences in initial and final carbonate chemistry and dissolved oxygen concentrations. All species experienced increases in rate of CO2 uptake and Q under elevated pCO2 treatments, but response level differed across species. Saccharina latissima had the greatest relative effect on all parameters measured, consuming 4 times more carbon at high pCO2 levels than the lowest performing species. While all macrophytes were able to raise Ωcalcite, the magnitude of change decreased at higher pCO2 levels, suggesting a limitation to the degree to which photosynthesis can locally raise calcification potential for sensitive native or farmed populations of shellfish in the future. The varied responses observed across species have implications for future community structures and for phytoremediation efforts.
- Publication:
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American Geophysical Union, Ocean Sciences Meeting
- Pub Date:
- February 2016
- Bibcode:
- 2016AGUOSED14A1613F
- Keywords:
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- 0810 Post-secondary education;
- EDUCATIONDE: 0855 Diversity;
- EDUCATIONDE: 6630 Workforce;
- PUBLIC ISSUES