DEPTH-DEPENDENT TEMPERATURE VARIABILITY IN THE SOUTHERN CALIFORNIA BIGHT WITH IMPLICATIONS FOR SURVIVAL OF THE COLD-WATER GORGONIAN OCTOCORAL <i>Adelogorgia phyllosclera</i>
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Gugliotti, Elizabeth Fraser
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Abstract
Water temperature is an important determinant of cold-water coral distribution as these taxa are adapted to stenothermal conditions. In recent years, several marine heatwave events have impacted marine ecosystems, including in the northeast Pacific Ocean. However, little is known about how these extreme ocean temperatures might impact cold-water corals. Determining the upper thermal limits of cold-water octocorals is an important first step in identifying if these warm-water events pose a potential threat. Accordingly, temperature data loggers were placed in the Channel Islands National Marine Sanctuary (CINMS) prior to the 2015-2016 El Niño Southern Oscillation (ENSO) event. High frequency data from these temperature loggers and historical temperature data from the California Cooperative Fisheries Investigations (CalCOFI) indicated that warm-water anomalies occurred frequently at 50 and 100 m and most anomalies occurred during strong ENSO months. Live colonies of the common gorgonian octocoral, <i>Adelogorgia phyllosclera</i>, were collected from the CINMS using a remotely operated vehicle (ROV). A laboratory study investigated the health, polyp activity and estimated survival of <i>A. phyllosclera</i> through a series of thermal exposure assays. Results of the temperature analysis indicated that warm-water anomalies occurred frequently at 50 and 100 m, with most of these falling during strong ENSO months. The experimental results suggest that the upper thermal limit of <i>A. phyllosclera</i> could lie near 20℃. This upper thermal limit was not exceeded frequently during the 2015-2016 ENSO event. Understanding the thermal stress responses of cold-water corals enables prediction of their resilience to predicted ocean warming.