Ocean Acidification

The burning of fossil fuels has increased atmospheric CO₂ at an unprecedented rate. The world’s oceans have absorbed much of this carbon dioxide, resulting in a decrease of pH and an increase in the partial pressure of CO2 in seawater in a process referred to as ocean acidification. Ocean acidification (OA) can cause a variety of detrimental effects on the physiology and ecology of larval fishes. Despite a preponderance of negative effects, studies of how OA affects the early life stages of fishes have produced mixed results and have tended to focus on a limited set of responses. In this study, I tested the effects of OA on energy intake, as measured by feeding rate, and energy expenditure, as measured by metabolic rate, then compared these results to growth and development in the California grunion (Leuresthes tenuis). I also created family groupings to analyze genetic variation underlying these responses. My pCO2 treatments ranged from a control with a central value of 550 μatm, followed by 1080 μatm, 1760 μatm, and 2820 μatm. Each experiment lasted for a period of 12 days, and I ran a total of 12 experiments. Within an experiment, measures of metabolic rate, feeding rate, growth, and development were conducted multiple times. Mortality rates were measured continuously. By analyzing the similarities in the responses of related larvae to CO2, I was able to estimate broad sense heritability’s for metabolic rate, feeding rate, growth, and mortality. I found that at 6-days post hatch, larvae developing in high CO2 conditions exerted significantly more energy on routine metabolic rate. This increase in energetic expenditure with CO2 was not matched by an increase in feeding. Paradoxically, however, growth in mass had a positive relationship with CO2. To explore the consequences of these results, I examined development via allometric analysis of organ growth. I found that the relative growth of the eyes and stomachs of larvae were significantly slower when larvae developed under high pCO2 conditions. Furthermore, I found that both growth and metabolic rates showed significant genetic variation in sensitivity to OA, suggesting considerable evolutionary potential in these traits. I also present evidence that maternal effects are highly influential within the first 6 days after hatch. Overall, my results suggest that OA can cause both an energy deficit and abnormalities in the development of California grunion. The developmental abnormalities observed may be a symptom of an allocation of resources that prioritizes growth at the expense of internal organ development. These changes are likely to have long-term effects on recruitment in natural populations. Additionally, our results suggest that there is appreciable standing genetic variation within the population for the phenotypes studied here.

Cole T. R., 2026. Effects of ocean acidification on the energetics and larval development of a coastal fish, the California grunion (Leuresthes tenuis). MSc thesis, California State University, 77 p. Thesis.