As the process of ocean acidification alters seawater carbon chemistry, physiological processes such as skeletal accretion are expected to become more difficult for calcifying organisms. The crustose coralline red algae (Corallinales, Rhodophyta) form an important guild of calcifying primary producers in the temperate Northeast Pacific. The morphology of important ecological traits, namely skeletal density and thallus thickness near the growing edge, were evaluated inPseudolithophyllum muricatum (Foslie) Steneck & R.T. Paine, the competitively dominant alga within this guild. Pseudolithophyllum muricatum shows a morphological response to increased ocean acidification in the temperate Northeast Pacific. Comparing historical (1981-1997) and modern (2012) samples from the field, crust thickness near the growing edge was approximately half as thick in modern samples compared with historical samples, while crust calcite density showed no significant change between the two sample groups. Morphological changes at the growing edge have important consequences for mediating competitive interactions within this guild of algae, and may affect the role of crustose coralline algal beds as hosts to infaunal communities and facilitators of recruitment in many invertebrate and macroalgal species.

McCoy S. J., in press. Morphology of the crustose coralline alga Pseudolithophyllum muricatum (Corallinales, Rhodophyta) responds to 30 years of ocean acidification in the Northeast Pacific. Journal of Phycology. Article (subscription required).