In this project we investigated the effect of ocean acidification and extreme climatic events on California coastal marine ecosystem by focusing primarily on three important calcifying species of conservation and fishery interest, namely, the red, green and pink abalone. To study this problem, we used a unique combination of (a) field data to characterize exposure to climatic stressors (warming, hypoxia, acidification) along the Pacific coast,  (b) cutting edge ocean models to quantify exposure of coastal abalone populations to these stressors in future climate scenarios, (c) novel laboratory experiments with variable stressors to elucidate effects of exposure on larvae and juvenile abalone, and (d) a new generation of population dynamics models to estimate for the first time the impact of ongoing and future climate change on abalone conservation and fishery management.

Our work provided key insights concerning the potential effects of future ocean changes for calcifying species in the California coast. The analysis of ocean data documented immense variability in exposure both at the regional and local scales, with frequent but short low oxygen and low pH events in central California and more persistent and intensive events in Baja California. According to oceanographic simulations, the intensity, frequency and duration of these events is projected to increase under climate change.  Laboratory experiments that simulated tidal cycles under present and future regimes of climate change showed that fertilization success (a key process for abalone reproduction) was not very sensitive to low oxygen in water but it was strongly affected by an increase in ocean acidification. The effect was not linear, i.e., there was a tipping point in ocean acidification, beyond which fertilization dramatically decreases. Yet, this negative effect was partially compensated by a temperature increase.

Laboratory experiments also showed that juvenile abalone grow slower under projected levels of ocean acidification. While differences in body size might seem minimal, our demographic models showed that a small reduction in body growth might have a multiplicative impact on the persistence and productivity of abalone populations, as mortality is higher and fecundity lower in small abalones. Both laboratory experiments and modelling simulations showed that indirect effects of ocean acidification and extreme climatic events – i.e., those effects mediated by species interaction, whether through predation, marine disease or ecological competition for space and resources - can be relevant and contribute to shape our future ocean ecosystem.

Our modelling simulations also showed that the combination of fishing mortality and natural mortality caused by heat waves or low oxygen, highly acidic water increased the likelihood that harvested populations drop below the density at which breeding success collapses making species particularly vulnerable to local extinction. Anyway, there is a bright spot in our research: our models showed that suitable network of marine protected areas can preserve pockets of high density populations with large, highly fecund abalone which, altogether, enhance reproductive success in spite of climate change, and allow to supplement recruitment outside the protected areas where abalone are intensively harvested, thus maintaining fishery catch. Therefore, it is possible to partially compensate the combined effect of climate change and fishing mortality via spatial management of fishing effort, a win-win solution that is good for nature and people. This is especially intriguing given the high variability in exposure we documented over small spatial scales.

The results of our project, summarized also at our web site https://upwelling.stanford.edu, contributed to the growing body of knowledge on how animals in the ocean may respond to future climate conditions and that variability in conditions at short time-scales has a strong potential to mediate these outcomes. How variability alters the response of populations will have enormous ramifications for not only our understanding of what the future ocean may look like, but also how integrated social-economic systems that depend on the ocean, such as fisheries, may be affected by future ocean change. In addition to these results, our project also designed and built a unique, highly sophisticated upwelling experimental system able to reproduce how cycles (tides, solar, weather) modulate oxygen, pH and temperature in time and thus to simulate in more realistic terms the effect of alternative scenarios of increasing frequency, intensity and durations of extreme events.

To support STEM education, we offered lectures, seminars and courses on ocean acidification and climate change and provided research opportunities in our laboratories for high school girls, underrepresented minorities, college, graduate and post-doctoral students. As it is crucial to promote awareness of the problem in the new generation of tomorrow’s leaders, we also developed a unique Ocean Acidification Activity Book, in English and Spanish, to introduce late-elementary and early-middle school students to the complex problem of ocean acidification, its direct and indirect impacts on the integrity of our ocean, and simple ways we can all contribute to reduce the cause of ocean acidification and climate change, i.e., human emissions of carbon dioxide.

Last Modified: 09/29/2018
Modified by: C. Brock Woodson