Skeletal trade-offs in coralline algae in response to ocean acidification

• Published in: Nature climate change 2014-08, Vol.4 (8), p.719-723
• Main Authors: McCoy, S. J., Ragazzola, F.
• Format: Article
• Language: English
• Subjects: 121/135; 631/158/853; 704/158/2165; Acidification; Algae; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; Calcium carbonate; Chemical analysis; Climate Change; Climate Change/Climate Change Impacts; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on plants and fungi; Environment; Environmental Law/Policy/Ecojustice; Fundamental and applied biological sciences. Psychology; letter; Marine environment; Observational studies; Ocean acidification; Physiological responses; Seawater; Water analysis
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/nclimate2273

Crustose coralline algae (CCA) are potential ‘poster children’ of ocean acidification stress, yet their stress responses have been poorly studied in a natural or ecological context. Now, a comparison of historical and modern specimens from a site with a declining pH trend over a 30-year period reveals trade-offs in skeletal traits tied to calcium carbonate use in response to ocean acidification in four CCA species. Ocean acidification is changing the marine environment, with potentially serious consequences for many organisms. Much of our understanding of ocean acidification effects comes from laboratory experiments, which demonstrate physiological responses over relatively short timescales 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . Observational studies and, more recently, experimental studies in natural systems suggest that ocean acidification will alter the structure of seaweed communities 11 , 12 , 13 . Here, we provide a mechanistic understanding of altered competitive dynamics among a group of seaweeds, the crustose coralline algae (CCA). We compare CCA from historical experiments (1981–1997) with specimens from recent, identical experiments (2012) to describe morphological changes over this time period, which coincides with acidification of seawater in the Northeastern Pacific 14 , 15 , 16 . Traditionally thick species decreased in thickness by a factor of 2.0–2.3, but did not experience a change in internal skeletal metrics. In contrast, traditionally thin species remained approximately the same thickness but reduced their total carbonate tissue by making thinner inter-filament cell walls. These changes represent alternative mechanisms for the reduction of calcium carbonate production in CCA and suggest energetic trade-offs related to the cost of building and maintaining a calcium carbonate skeleton as pH declines. Our classification of stress response by morphological type may be generalizable to CCA at other sites, as well as to other calcifying organisms with species-specific differences in morphological types.