Catriona L. Hurd
Institute of Marine and Antarctic Studies, University of Tasmania, Hobart, Australia.
Since ~1750, the world’s oceans have absorbed 40% of the CO2 released by human industrial activities, resulting in ongoing alterations to the seawater carbonate system: in surface waters, levels of dissolved CO2 and H+ are predicted to increase by ~150% by 2100 resulting in a 0.4 reduction in pH and a 55% decline in the saturation state of calcium carbonate (Ω) – each of these factors has implications for the ability of calcifying organism (e.g. coralline algae, molluscs, sea urchins) to maintain net calcification. However, compared to the open ocean pH in coastal waters is highly variable due to biological activity, particularly from primary producers because photosynthesis causes H+ (and hence pH) to increase during the day, whereas at night pH declines due to respiration. Kelp forests also attenuate seawater flow, which leads to seawater within and near to the beds having a higher pH than that of the surrounding seawater. Kelp beds have therefore been implicated as refugia for calcifying organisms from future ocean acidification: Here I will discuss evidence for this.