title: Ocean acidification reverses the positive effects of seawater pH fluctuations on growth and photosynthesis of the habitat-forming kelp, Ecklonia radiata.
abstract: Ocean acidification (OA) is the reduction in seawater pH due to the absorption of human-released CO2 by the world's oceans. The average surface oceanic pH is predicted to decline by 0.4 units by 2100. However, kelp metabolically modifies seawater pH via photosynthesis and respiration in some temperate coastal systems, resulting in daily pH fluctuations of up to ±0.45 units. It is unknown how these fluctuations in pH influence the growth and physiology of the kelp, or how this might change with OA. In laboratory experiments that mimicked the most extreme pH fluctuations measured within beds of the canopy-forming kelp Ecklonia radiata in Tasmania, the growth and photosynthetic rates of juvenile E. radiata were greater under fluctuating pH (8.4 in the day, 7.8 at night) than in static pH treatments (8.4, 8.1, 7.8). However, pH fluctuations had no effect on growth rates and a negative effect on photosynthesis when the mean pH of each treatment was reduced by 0.3 units. Currently, pH fluctuations have a positive effect on E. radiata but this effect could be reversed in the future under OA, which is likely to impact the future ecological dynamics and productivity of habitats dominated by E. radiata.
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7001, Australia.
authors.forename: Damon
authors.initials: D
authors.lastname: Britton
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7001, Australia.|School of Earth and Environment, Oceans Institute, &ARC Centre of Excellence for Coral Reef Studies, University of Western Australia, Crawley, WA 6009, Australia.
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Cornwall
authors.affiliation: CSIRO Oceans and Atmosphere, Hobart, TAS, Australia.
authors.forename: Andrew T
authors.initials: AT
authors.lastname: Revill
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7001, Australia.
authors.forename: Catriona L
authors.initials: CL
authors.lastname: Hurd
authors.affiliation: Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS 7001, Australia.
authors.forename: Craig R
authors.initials: CR
authors.lastname: Johnson
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D048708:Cell Growth Processes; D057231:Climate Change; D017753:Ecosystem; D006863:Hydrogen-Ion Concentration; D008386:Marine Biology; D009792:Oceans and Seas; D000459:Phaeophyceae / Q000502:physiology*; D010788:Photosynthesis; D012623:Seawater / Q000737:chemistry*; D013648:Tasmania
chemical_list: D002245:Carbon Dioxide