Photosynthetic activity buffers ocean acidification in seagrass meadows

Authors

I. E. Hendriks, Instituto Mediterráneo de Estudios Avanzados
Y. S. Olsen, Instituto Mediterráneo de Estudios Avanzados; University of Western Australia
L. Ramajo, Instituto Mediterráneo de Estudios Avanzados; Facultad de Ciencias Universidad Santo Tomás
L. Basso, Instituto Mediterráneo de Estudios Avanzados
T. S. Moore, Instituto Mediterráneo de Estudios Avanzados
J. Howard, Department of Biological Sciences, Florida International University
C. M. Duarte, Instituto Mediterráneo de Estudios Avanzados; University of Western Australia

Date of this Version

1-28-2014

Document Type

Article

Abstract

Macrophytes growing in shallow coastal zones characterised by intense metabolic activity have the capacity to modify pH within their canopy and beyond. We observed diel pH changes in shallow (5–12 m) seagrass (Posidonia oceanica) meadows spanning 0.06 pH units in September to 0.24 units in June. The carbonate system (pH, DIC, and aragonite saturation state (Ω_Ar)) and O₂ within the meadows displayed strong diel variability driven by primary productivity, and changes in chemistry were related to structural parameters of the meadow, in particular, the leaf surface area available for photosynthesis (LAI). LAI was positively correlated to mean, max and range pH_NBS and max and range Ω_Ar. In June, vertical mixing (as Turbulent Kinetic Energy) influenced max and min Ω_Ar, while in September there was no effect of hydrodynamics on the carbonate system within the canopy. Max and range Ω_Ar within the meadow showed a positive trend with the calcium carbonate load of the leaves, pointing to a possible link between structural parameters, Ω_Ar and carbonate deposition. Calcifying organisms, e.g. epiphytes with carbonate skeletons, may benefit from the modification of the carbonate system by the meadow. There is, however, concern for the ability of seagrasses to provide modifications of similar importance in the future. The predicted decline of seagrass meadows may alter the scope for alteration of pH within a seagrass meadow and in the water column above the meadow, particularly if shoot density and biomass decline, on which LAI is based. Organisms associated with seagrass communities may therefore suffer from the loss of pH buffering capacity in degraded meadows.

Comments

Originally published in Biogeosciences.

Creative Commons License

This work is licensed under a Creative Commons Attribution 3.0 License.

Recommended Citation

Hendriks, I. E., Olsen, Y. S., Ramajo, L., Basso, L., Steckbauer, A., Moore, T. S., Howard, J., and Duarte, C. M.: Photosynthetic activity buffers ocean acidification in seagrass meadows, Biogeosciences, 11, 333-346, doi:10.5194/bg-11-333-2014, 2014.