Date

Fall 2021

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

The California Current ecosystem is experiencing dramatic changes in ocean chemistry resulting in ocean acidification (i.e., decreasing pH) and lower dissolved oxygen [DO] levels. These changes are exacerbated by increases in upwelling intensity and the shoaling of the oxygen minimum zone. Gopher rockfish (Sebastes carnatus) and blue rockfish (Sebastes mystinus) are ecologically and economically valuable rockfish species, whose habitat is becoming increasingly inundated with low pH and low DO water. To test how ocean acidification and hypoxia may interact to influence the reproductive process in rockfishes, I exposed gravid females of both species to four treatments throughout the gestation period: 1) low pH (7.5); 2) low DO (DO 4.0 mg/L); 3) combined stressor (7.5 pH x DO 4.0 mg/L); and 4) control (~8.0 pH x ~DO 8.0). Post-parturition, larvae from each brood were seeded into each of the four treatments to evaluate survivorship, metabolism, and hypoxia tolerance as a function of the prior maternal treatment conditions and the subsequent larval treatment. I assessed the impact of maternal rockfish exposure to climate change stressors on fecundity, percent deformity, and larval morphology. My research indicates that Gopher rockfish larvae are resilient to low pH (pH 7.5) and low DO (DO 4.0mg/L) based on both maternal and larval exposures to these stressors. Gopher rockfish may be adapted or acclimatized to gestating in these conditions because their reproductive season overlaps with Spring upwelling on the central California coast. Blue rockfish also exhibited resiliency; larval survivorship, metabolic rate, hypoxia tolerance, and percent deformity were not impacted by low pH, low DO or combined stressor. However, blue rockfish larval morphology was impacted by gestating in the combined stressor treatment, resulting in a reduction in larval eye size. Adult blue rockfish peak reproductive season is in winter and they may not be as well adapted or acclimatized to gestating in upwelling conditions as gopher rockfish. While both gopher rockfish and blue rockfish had predominantly successful broods in 7.5 pH, 4.0 mg/L DO, and combined stressor (7.5 pH x 4.0 mg/L) treatments, it is unknown how they will respond to more extreme low pH and low DO events that are projected to become more common in the California Current coastal habitat as climate change progresses.

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