Impact of crustose coralline algae, ocean acidification, and ocean warming on larval pinto abalone settlement and juvenile survival

Since 1994, Washington State (USA) has experienced a 97 % drop in the native pinto abalone population. Since 2007, conservation aquaculture initiatives have been underway to return the population to a self-sustaining level. Successful restoration, however, depends on both the ability to successfully raise juveniles in hatchery settings and the capacity of outplanted pinto abalone to survive and reproduce in the wild as threats of ocean acidification and warming continue to increase. Crustose coralline algae (CCA) can play an important role in restoration efforts by acting as natural inducers of larval settlement. Additionally, studies have shown that CCA can create a boundary layer with elevated pH, potentially providing a refuge for benthic species. We examined the settlement of pinto abalone under different environmental conditions (7.90 pH/14 °C (ambient), 7.90 pH/18 °C, 7.55 pH/14 °C; and 7.55 pH/18 °C) using two substrates: CCA-covered rocks and clean rocks with GABA (a chemical settlement inducer). Low pH negatively impacted larval settlement. Though settlement was higher with CCA than with GABA, this difference was not statistically significant. Juvenile survival was negatively impacted by low pH, but positively impacted by CCA presence, demonstrating the potential of CCA to increase juvenile pinto abalone survival and ameliorate the negative effects of low pH. Using CCA in hatchery culture and selecting sites with CCA cover for pinto abalone outplants may improve the efficiency of restoration in Washington. • Ocean acidification reduced pinto abalone settlement and survival in the hatchery. • Ocean acidification is likely a greater threat than warming to Washington pinto abalone. • Use of a natural settlement inducer improves abalone settlement and survival. • Coralline algae may improve survival of pinto abalone under ocean acidification.