The role of macroalgal habitats as ocean acidification refugia within coastal seascapes

Abstract

Ocean acidification (OA) refers to a global decline in the average pH of seawater driven by the absorption of atmospheric carbon dioxide (CO 2 ). Marine macroalgae, while affected by this pH change, are also able to modify seawater pH through their own interaction with inorganic carbon in the carbonate system. Through this action, macroalgae-dominated habitats are potential refugia from OA for associated marine species. This review summarises the most prominent literature on the role of macroalgae in OA mitigation and the potential of macroalgal habitats to serve as OA refugia. It includes a brief overview of macroalgal distribution in an effort to illustrate where such refugia might be most prevalent. Macroalgae influence seawater carbonate chemistry through the absorption of CO 2 and HCO 3 (cid:1) during photosynthesis, raising surrounding seawater pH in the process. This transient effect on seawater chemistry could provide some respite from the negative effects of OA for many marine species. This refuge role varies over a range of scales along with macroalgal architecture, which varies in size from low-growing turfs to large canopy-forming stands. The associated pH changes can range over various temporal (daily and seasonal) and spatial (from centimetre to kilometre) scales. Areas of high macroalgal biomass are likely to play an important role as significant OA refugia. Such communities are distributed widely throughout the globe. Large brown macroalgae (Laminariales) dominated communities are common in temperate regions, while members of the Fucales are responsible for substantial macroalgal stands in warmer tropical regions. These marine fields and forests have great potential to serve as localised refuges from OA. While more work needs to be done to clarify the effect of macroalgal communities on seawater pH