Identifying South African Marine Protected Areas at risk from marine heatwaves and cold spells
Abstract
Marine thermal extremes (i.e. marine heatwaves (MHWs) and marine cold-spells (MCSs)) are not currently accounted for in the design of South Africa’s Marine Protected Area (MPA) network. As such, the implications of thermal extremes cannot be addressed through spatial conservation management. Consequently, this study aimed to characterize MHWs and MCSs in MPAs across the six South African marine ecoregions. In so doing, a novel index was developed to enable the comparison of thermal event severity and the relative challenge posed by extreme thermal events in each MPA. Thermal events declined in duration and intensity from west to east, with the least severe thermal events recorded in the Delagoa ecoregion. Walker Bay MPA, within the Agulhas ecoregion, was identified as the MPA most at risk from extreme thermal events, with MHW and MCS severity indices almost double that of any other MPA. These thermal events may challenge the ability of this cetacean sanctuary MPA to meet its primary conservation objectives, as climate-driven changes in temperature can affect whale distribution, movement and reproduction. Understanding the variation in nature of thermal extremes across ecoregions and among MPAs will assist in prioritizing sites for in situ monitoring of water temperatures and studies of the local impacts of extreme thermal events, as well as identifying areas for expansion of refugia. Notably, if past trends in the number and cumulative intensity of MHWs are indicative of future trends, 62% of South African MPAs could experience more severe heatwaves in the future. The use of this approach to identify MPAs most vulnerable to thermal events can help to support adaptive management and secure the effectiveness of MPAs into the future.