Effects of warm ocean temperatures on bull kelp forests in the Salish Sea

Kelp beds are marine sanctuaries, providing some of the most productive ecosystems on the planet and serving as critical habitat and refuge for many species, including juvenile salmon. Rising ocean temperature associated with climate change is a major stressor contributing to declines of kelp forests worldwide. In the Salish Sea, we identified bull kelp (Nereocystis leutkeana) populations growing under two different temperature regimes. Since 2011, kelp growing in the central Strait of Georgia has been exposed to sea surface temperatures (SSTs) of 15-21 degreesC in the summer months, which is 5-6 degreesC warmer than temperatures in the Strait of Juan De Fuca. To assess the effects of high summer SSTs, populations growing at a warm and a cold site (Stanley Park and French Beach respectively) were sampled in the summer and fall of 2017. Warmer summer SSTs at Stanley Park correlated with significant declines in spore production, indicating negative effects on the reproductive capacity of that population. Growth and development of healthy spores from either population was reduced when incubated in the lab at temperatures above ~ 17 degreesC and temperatures of ~ 20 degreesC resulted in mortality of nearly all spores. Analyses of stress levels in spores exposed to different temperatures, based on the production of reactive oxygen species, is now underway. This research continues to provide crucial data needed for habitat restoration efforts as they will allow for the selection of stress-resilient kelp stocks that are better adapted for survival in warmer oceans.