A climate sensitive watch list for alien species in South African kelp forests

Following establishment, the probability of successful eradication of marine alien species is limited.In the context of kelp forest systems, this is particularly concerning as alien species can lead to dramatic changes in ecosystem structure and even the total loss of kelp.In South Africa, little is known about the status of alien species in kelp forests and there is a need for regular monitoring to support the early detection of incursions and maximise the potential for effective management interventions.However, limited resources dictate that monitoring be done in a cost-efficient manner.Watch lists can support such monitoring.In this study a watch list of alien species with the potential to invade South African kelp forests was developed through a climate-sensitive horizon-scanning approach that accounted for current conditions and predicted climate change.Temperature-matching was used to determine the suitability of the Benguela and Agulhas ecoregions for the watch list species under present and future climatic conditions.The watch list included seven species (the bryozoan Membranipora membranacea, and the algae Bonnemaisonia hamifera, Dasysiphonia japonica, Fucus serratus, Sargassum muticum, Sargassum horneri, and Undaria pinnatifida), some of which have had profound impacts in kelp forest ecosystems in other parts of the world.Overall, kelp forests in the cool temperate Benguela ecoregion appear most vulnerable to invasion, as current and future conditions closely match those under which the watch list species are known to occur elsewhere.This, together with the presence of important ports in the region, highlights the vulnerability of South African west coast kelp forests to invasions and the potential impacts that could result.