Date

Spring 2019

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Natural Sciences

Abstract

In the Northeast Pacific, seasonal upwelling periodically exposes nearshore organisms to elevated levels of pCO 2 and hypoxia. Upwelling is projected to intensify under climate change as more frequent and intense alongshore wind events bring deeper, more acidic and hypoxic seawater to shallower depths and into nearshore ecosystems. Previous work demonstrated that blue rockfish (Sebastes mystinus) are relatively tolerant to high levels of pCO 2 at multiple biological scales compared with copper rockfish (S. caurinus) following chronic exposure for multiple months. To investigate the tolerance of juvenile blue rockfish over shorter, more ecologically relevant periods, I measured changes in muscle tissue gene expression at 12 h, 24 h and two weeks of exposure to elevated pCO 2 (1200 µatm), hypoxia (4.0 mg/L) and combined high pCO2/hypoxia. I also measured the activities of key metabolic enzymes (citrate synthase and lactate dehydrogenase) under combined high pCO 2 /hypoxia to assess the stressors' effects at the biochemical level. I found that gene expression patterns over time varied significantly among the three treatments, with little functional overlap among genes responsive to each treatment. In response to elevated pCO 2 , blue rockfish increased expression of genes encoding muscular contractile proteins as well as genes involved in ATP metabolism pathways, possibly indicating shifts in muscle composition and heightened basal metabolism. Under hypoxia, blue rockfish also up-regulated genes encoding ATP metabolic proteins, but also up-regulated important ionoregulatory proteins like carbonic anhydrase. Under combined high pCO 2 and hypoxia, I observed differential expression of genes involved in various signaling pathways and oxygen carrying capacity, but observed no changes in metabolic enzyme activities. While blue rockfish up-regulated many of the same genes under combined high pCO 2 /hypoxia that were observed under each independent stressor, the response under both stressors was not additive but varied with exposure time between synergism and antagonism. My findings indicate that juvenile blue rockfish may be equipped to cope with moderate high pCO2 and hypoxia in the short term, and that the species may be sufficiently responsive to employ different gene suites under each stressor. If rockfishes in general display tolerance to these stressors, annual recruitment may continue to play a larger role in determining abundances than climate-related oceanographic shifts. If changing conditions are shown to adversely impact some rockfish species more than others, however, environmental forecasting data may merit inclusion in California groundfish fishery management.

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