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Marine Ecology Progress Series

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MEPS 595:55-69 (2018)  -  DOI:

Ocean warming has greater and more consistent negative effects than ocean acidification on the growth and health of subtropical macroalgae

Alexia Graba-Landry1,2,*, Andrew S. Hoey2, Jordan K. Matley3, Hannah Sheppard-Brennand1, Alistair G. B. Poore4, Maria Byrne5, Symon A. Dworjanyn1

1National Marine Science Centre, Southern Cross University, PO Box J321, Coffs Harbour, NSW 2450, Australia
2ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia
3Centre for Marine and Environmental Studies, University of the Virgin Islands, St. Thomas, VI 00802, USA
4Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia
5Schools of Medical and Life and Environmental Sciences, University of Sydney, Sydney, NSW 2006, Australia
*Corresponding author:

ABSTRACT: Macroalgae are the major habitat-forming organisms in many coastal temperate and subtropical marine systems. Although climate change has been identified as a major threat to the persistence of macroalgal beds, the combined effects of ocean warming and ocean acidification on algal performance are poorly understood. Here we investigate the effects of increased temperature and acidification on the growth, calcification and nutritional content of 6 common subtropical macroalgae; Sargassum linearifolium, Ulva sp., Amphiroa anceps, Corallina officinalis, Delisea pulchra and Laurencia decussata. Algae were reared in a factorial cross of 3 temperatures (23°C [ambient], 26°C and 28°C) and 3 pH levels (8.1 [ambient], 7.8 and 7.6) for 2 wk. The highest (28°C) temperature decreased the growth of all 6 macroalgal species, irrespective of the pH levels. In contrast, the effect of decreased pH on growth was variable. The growth of Ulva sp. and C. officinalis increased, L. decussata decreased, while the remaining 3 species were unaffected. Interestingly, the differential responses of macroalgae to ocean acidification were unrelated to whether or not a species was a calcifying alga, or their carbon-uptake mechanism—2 processes that are predicted to be sensitive to decreased pH. The growth of the calcifying algae (C. officinalis and A. anceps) was not affected by reduced pH but calcification of these 2 algae was reduced when exposed to a combination of reduced pH and elevated temperature. The 3 species capable of uptake of bicarbonate, S. linearifolium, L. decussata and Ulva sp., displayed positive, negative and neutral changes in growth, respectively, in response to reduced pH. The C:N ratio for 5 of the 6 species was unaffected by either pH or temperature. The consistent and predictable negative effects of temperature on the growth and calcification of subtropical macroalgae suggests that this stressor poses a greater threat to the persistence of subtropical macroalgal populations than ocean acidification under ongoing and future climate change.

KEY WORDS: Carbon-concentrating mechanisms · Primary production · Climate change · Coralline algae · Macroalgae

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Cite this article as: Graba-Landry A, Hoey AS, Matley JK, Sheppard-Brennand H, Poore AGB, Byrne M, Dworjanyn SA (2018) Ocean warming has greater and more consistent negative effects than ocean acidification on the growth and health of subtropical macroalgae. Mar Ecol Prog Ser 595:55-69.

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