Co‐creating solutions to the hidden impacts of climate change on Canada's Pacific kelp forests

Abstract Co‐designed research driven by the information needs of coastal communities can enhance social‐ecological resilience to climate change. On the Central Coast of British Columbia, Canada, the 2014–2015 marine heatwave triggered an outbreak of an encrusting bryozoan ( Membranipora spp.) on giant kelp ( Macrocystis tenuifolia ), an ecologically, culturally and economically important seaweed to coastal Indigenous Peoples that is also under direct threat from ocean warming and extreme heat events. In response, Indigenous stewardship departments and academic researchers co‐designed field surveys examining potential impacts of bryozoans on kelp at 10 sites over 2 years, encompassing spatial and interannual variation in ocean temperatures. The susceptibility of kelp beds to bryozoan outbreaks increased with higher kelp canopy cover and warmer sea surface temperatures yet decreased with greater wave exposure. During 2021, maximum bryozoan cover on kelp occurred ≈2.5 months earlier than in 2020, which correlated with the timing of anomalously early warming of seawater. This result illustrates how ocean warming can indirectly impact kelp. Adaptive management strategies include selection of cooler and more wave‐exposed sites for kelp harvests, reduced harvests in warmer years and seasonally earlier harvests during years with anomalously early warming. Our study demonstrates how engagement with local knowledge holders and collaborative monitoring can inform adaptive management strategies aimed at increasing social‐ecological resilience at local scales relevant to Indigenous governance and coastal economies. Read the free Plain Language Summary for this article on the Journal blog.