Absorption of anthropogenic CO2 by the world’s oceans is decreasing ocean pH globally, resulting in the phenomenon termed ocean acidification (OA). Some surface waters of the California Current System (CCS) found along the West Coast of North America are naturally exposed to low-pH conditions when acidic deeper-ocean water is lifted into nearshore habitats during seasonal upwelling. Variation in this process creates a mosaic of pH conditions along the West Coast, and populations of organisms inhabiting particular sectors of this mosaic may be pre-adapted to future OA through selection imposed by this recurring historical exposure to low-pH conditions. We compared the response of two populations of red abalone (Haliotis rufescens), a marine species of conservation concern, sourced from different regions of the CCS; one that experiences high levels of upwelling activity (Mendocino, CA) and one that experiences less intense upwelling (Santa Barbara, CA). Animals were cultured from the embryonic stage to post settlement juveniles under both contemporary pH values (8.1 pH, 400 μatm CO2) and acidic conditions that are experienced now during upwelling (7.6 pH, 1200 μatm CO2) and which are expected to become increasingly common in the future.
Results/Conclusions
Abalone sourced from Mendocino exhibited significantly greater lipid concentrations during the larval and post-settlement phases. We failed to observe any reduction in survival in this population under low pH, whereas a 40% reduction in survival was observed in the Santa Barbara population. Moreover, this response varied significantly with settlement habitat (crustose coralline algae vs. diatoms) indicating that the effects of OA can be modulated by complex factors in nature. Notably, a minority of family lineages from the Santa Barbara population were resilient to OA, failing to exhibit a significant increase in mortality under high CO2 exposure. These results suggest that OA-resistant genotype combinations exist within the abalone metapopulation, which may be adaptive in future environments. The heritability of these differences is now being investigated through trials on second generation offspring, with the goal of identifying adaptive genetic variation for use in future abalone aquaculture and conservation.