Coastal ecosystems that are characterized by kelp forests encounter daily pH fluctuations, driven by photosynthesis and respiration, which are larger than pH changes owing to ocean acidification (OA) projected for surface ocean waters by 2100. We investigated whether mimicry of biologically mediated diurnal shifts in pH—based for the first time on pH time-series measurements within a kelp forest—would offset or amplify the negative effects of OA on calcifiers. In a 40-day laboratory experiment, the calcifying coralline macro- alga, Arthrocardia corymbosa, was exposed to two mean pH treatments (8.05 or 7.65). For each mean, two experimental pH manipulations were applied. In one treatment, pH was held constant. In the second treatment, pH was manipulated around the mean (as a step-function), 0.4 pH units higher during daylight and 0.4 units lower during darkness to approximate diurnal fluctuations in a kelp forest. In all cases, growth rates were lower at a reduced mean pH, and fluctuations in pH acted additively to further reduce growth. Photosynthesis, recruitment and elemental composition did not change with pH, but d13C increased at lower mean pH. Including environmental hetero- geneity in experimental design will assist with a more accurate assessment of the responses of calcifiers to OA.

Item Type:	Refereed Article
Keywords:	ocean acidification
Research Division:	Environmental Sciences
Research Group:	Ecological Applications
Research Field:	Ecological Impacts of Climate Change
Objective Division:	Environment
Objective Group:	Climate and Climate Change
Objective Field:	Ecosystem Adaptation to Climate Change
UTAS Author:	Cornwall, CE (Dr Chris Cornwall)
UTAS Author:	Boyd, PW (Professor Philip Boyd)
UTAS Author:	Hurd, CL (Professor Catriona Hurd)
ID Code:	89038
Year Published:	2013
Web of Science® Times Cited:	82
Deposited By:	IMAS Research and Education Centre
Deposited On:	2014-02-24
Last Modified:	2014-06-12
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