COS 146-2 - Examining the reproductive success of bull kelp (Nereocystis luetkeana) under climate change conditions

Background/Question/Methods

Climate change has the potential to affect marine ecosystems through warming temperatures and ocean acidification. From 2013-2017, an extensive marine heatwave extended along the west coast of North America and had devastating effects on numerous species during this period, including bull kelp (Nereocystis luetkeana). Bull kelp is an important foundation species in coastal ecosystems, but the impacts of climate change events such as marine heat waves and ocean acidification on specific parts of the bull kelp life cycle have not been fully investigated. Previous work suggests increasing temperatures negatively affect kelp growth and survival, but that acidification can have positive impacts. To determine the effects of changing temperatures and carbonate levels on Northern California’s bull kelp populations, we collected sporophylls from mature bull kelp individuals in Point Arena, CA. At Bodega Marine Laboratory, we released spores and proceeded to culture microscopic bull kelp gametophytes in a common garden experiment with a factorial design crossing modern conditions (11.63±0.54°C and 7.93±0.26 pH) with projected future conditions under climate change (15.56±0.83°C and 7.64±0.32 pH). Our experiment sought to answer the question of how will increasing temperatures and decreasing pH impact the reproductive success of bull kelp?

Results/Conclusions

Our results found that both increasing temperatures and decreasing pH influenced growth and egg production of bull kelp microscopic stages. We found that increased temperature and decreased pH had interacting effects on both sporophyte growth and egg production. Increased temperature generally resulted in decreased in growth and egg production. In contrast, decreasing pH had less of an effect than temperature on growth and egg production, but generally resulted in increased growth and egg production. Our findings allow ecologists and managers to better predict the impacts of climate change on coastal ecosystems as well as providing key insight into environmental dynamics regulating the bull kelp lifecycle.