Understanding how climate change may influence ecosystems depends substantially on its effects on foundation species, such as the ecologically important giant kelp (Macrocystis pyrifera). Despite its broad distribution along strong temperature and pH gradients and strong barriers to dispersal, the potential for local adaptation to climate change variables among kelp populations remains poorly understood. We assessed this potential by exposing giant kelp early life stages from genetically disparate populations in Chile and California to current and projected temperature and pH levels in common garden experiments. We observed high resistance at the haploid life stage to elevated temperatures with developmental failure appearing at the egg and sporophyte production stages among Chilean and high-latitude California populations, suggesting a greater vulnerability to climate- or ENSO-driven warming events. Additionally, populations that experience low pH events via strong upwelling, internal waves, or estuarine processes, produced more eggs per female under experimental low-pH conditions, which could increase fertilization success. These results enhance our ability to predict population extinctions and ecosystem range shifts under projected declines in ocean pH and increases in ocean temperature.

In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2019) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation by seacarb is 2020-05-6.