Quantifying Physiological, Behavioral and Ecological Consequences of Hypoxic Events in Kelp Forest

Rocky reef kelp forests that extend along the coast of central California, like many habitats in upwelling systems, often experience inundations of low dissolved oxygen (DO) or hypoxic waters. These events have the potential to influence the structure and function of coastal ecosystems. The ecological consequences of hypoxia for these systems will be mediated by physiological thresholds and behavioral responses of resident organisms in the context of the spatial and temporal variability of DO, and other potential stressors. Our research focuses on Sebastes (i.e. rockfish) because of their commercial, recreational and ecological importance, high abundance across near shore habitats and the potentially severe impacts of physiological stress due to hypoxia. In the lab, to investigate how hypoxic events physiologically effect rockfish, we exposed young of the year (YOY) of 5 species and two life stages of blue rockfish, S. mystinus (YOY and 1+), to DO concentrations representative of upwelling conditions and measured a suite of whole organisms and tissue level responses including metabolic rate, ventilation, tissue-level metabolism, and blood biochemistry. Results demonstrate species and life stage specific differences in physiological stress under upwelling driven hypoxic conditions and suggest YOY rockfishes may currently be living near their physiological limits. In the laboratory we further explored if physiological impacts result in behavioral consequences by examining the startle response of YOY rockfish, a relative measure of predator avoidance ability, under a range of DO concentrations and exposure durations. To further explore behavioral responses of rockfish to low in DO within the kelp forest we are using two approaches, monitoring the vertical distribution of fish communities across the water column using an acoustic imaging camera (ARIS 3000, Soundmetrics Inc.) and acoustic tagging, with 3-D positioning ability (VPS, VEMCO Inc.), of larger blue rockfish . In conjunction with monitoring of in situ conditions and additional physiological lab studies on larger rockfish, we are using these approaches to develop a framework to understand how physiological limits and spatial and temporal variability in DO impact the behavior and ecology of rockfish in kelp forests within upwelling systems.