Moderate ocean alkalinity enhancement likely to have minimal effects on a habitat‐forming kelp across multiple life stages

Abstract

Ocean alkalinity enhancement (OAE) is a widely considered marine CO2 removal method. Ocean alkalinity enhancement works by converting seawater CO2 into and by electrochemical methods or the addition of alkaline minerals. Although OAE does not require biology to remove CO2, the perturbations caused by OAE may affect marine organisms. Due to logistical challenges, it is likely that alkalinity additions will occur in coastal regions, yet the effects on coastal species are unknown. Along temperate coasts, kelp forests are important communities that provide habitat for numerous species. However, it is unclear how kelps will respond to OAE and whether responses differ across life stages. To address this, we conducted a laboratory culture experiment on adults of the kelp Ecklonia radiata. Individuals were exposed to control, +300, and +600 μmol kg−1 alkalinity additions using NaOH as an alkalinity source. Following this, spores from reproductive adults cultured under control and +600 μmol kg−1 alkalinity treatments were released into control, +300, and +600 μmol kg−1 alkalinity conditions to determine the effect on the development of new recruits. Negative effects were only evident under extreme alkalinity enhancement conditions across both life stages. Adults displayed a decline in growth rates in the +600 μmol kg−1 treatment and less recruits developed from spores released into +600 μmol kg−1 alkalinity conditions. No negative effects were detected under +300 μmol kg−1 alkalinity increases across both life stages. These findings suggest chemical OAE methods are unlikely to have substantial impacts on E. radiata except under extreme conditions.