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 CO 2 removal method. Ocean alkalinity enhancement works by converting seawater CO 2 into and by electrochemical methods or the addition of alkaline minerals. Although OAE does not require biology to remove CO 2 , 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 μ mol kg −1 alkalinity additions using NaOH as an alkalinity source. Following this, spores from reproductive adults cultured under control and +600 μ mol kg −1 alkalinity treatments were released into control, +300, and +600 μ mol 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 μ mol kg −1 treatment and less recruits developed from spores released into +600 μ mol kg −1 alkalinity conditions. No negative effects were detected under +300 μ mol 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.