Implications of Pyrosoma atlanticum range expansion on phytoplankton standing stocks in the Northern California Current. (October 2020)

• Record Type: Journal Article
• Authors: O'Loughlin, Jessica H.; Bernard, Kim S.; Daly, Elizabeth A.; Zeman, Samantha; Fisher, Jennifer L.; Brodeur, Richard D.; Hurst, Thomas P.
• Is Part Of: Progress in oceanography. Volume 188(2020)
• Publication Date: 2020-10
• Subjects: Pyrosome -- Tunicate -- Abundance -- Grazing impact -- Northern California Current; Oceanography -- Periodicals; 551.4605
• DOI: 10.1016/j.pocean.2020.102424
• Languages: English
• ISSNs: 0079-6611

Abstract

Highlights: Blooms of pelagic tunicate, Pyrosoma atlanticum, found beyond typical range. Colonies of P. atlanticum doubled in size in less than two months off Oregon coast. P. atlanticum removed up to 22% phytoplankton stock daily off Oregon coast. Abstract: Coinciding with the marine heat wave in 2014 and a strong El Niño in 2016, blooms of the tropical-temperate pelagic colonial tunicate, Pyrosoma atlanticum, expanded into the Northern California Current (NCC). Given the high densities of P. atlanticum colonies observed in the NCC, and their potential for high grazing rates, we hypothesized that the species could have a substantial negative effect on the phytoplankton standing stock in the Northeastern Pacific Ocean. In the late winter, spring and early autumn of 2018, we measured abundances and length frequencies of P. atlanticum colonies off the coast of Oregon and estimated their spring grazing impact on the local phytoplankton standing stock. Abundances of P. atlanticum peaked in late winter (0.7 colonies m −3 ), dropped off in spring (0.42 colonies m −3 ), and declined to near-absent in early autumn (0.07 colonies m −3 ). We observed a doubling in the median size of P. atlanticum colonies from late winter to spring, followed by a decline in size in early autumn. With their high individual colony gut pigment contents and bloom densities, the overall spring grazing impact of P. atlanticum was substantial, reaching a maximum of 22% of the available phytoplankton standing stock.