DISTRIBUTION OF PELAGIC THALIACEANS, THETYS VAGINA AND PYROSOMA ATLANTICUM, DURING A PERIOD OF MASS OCCURRENCE WITHIN THE CALIFORNIA CURRENT

The spatial distribution, abundance, and size variability of two pelagic tunicate species, Thetys vagina and Pyrosoma atlanticutn, were examined from midwater trawl surveys to assess the historical context and geographical aspects of a major mass occurrence event throughout the California Current Large Marine Ecosystem during 2012-19. Off central California, abundance of both species were significantly greater in 2012-19 compared to 1983-2001, and their recent persistent multiyear abundance peaks were unprecedented. Coastwide abundance and distribution of T. vagina during 201319 was patchy, with no discernible shifts in distribution or changes in mean length. From 2013-18, abundance and distribution of P. atlanticum demonstrated a temporal trend of increasing abundance from south to north, and in northern areas, average P. atlanticum colony length increased over time. In 2019, high abundances of P. atlanticum occurred south of Monterey Bay, but were not found in the northern California Current. We discuss how in situ and regional-scale environmental drivers may have contributed to this recent multiyear gelatinous mass occurrence, and potential consequences to forage community structure and ecosystem function.