SEASONAL CHANGES IN TRICHODESMIUM CONCENTRATIONS AND SIZE IN THE NORTH PACIFIC SUBTROPICAL GYRE

Trichodesmium is considered one of the largest suppliers of bioavailable nitrogen in the oligotrophic gyres, potentially accounting for significant fractions of total nitrogen fixation and new production when abundant. This study examines seasonal changes in Trichodesmium abundance and size via near-monthly sampling of the North Pacific Subtropical Gyre in coordination with the Hawaiian Ocean Time-series. Multiple instruments were used to capture free filament and colony morphologies, which collectively span from tens of microns to up to a millimeter in size. Surface seawater was sampled with an Imaging Flow CytoBot (IFCB), imaging primarily single Trichodesmium filaments. A towed Digital Autonomous Video Plankton Recorder (VPR) imaged colonies (‘puffs’, ‘tufts’, and ‘bowties’) while undulating through the upper 100 m of the water column. Trichodesmium free filament and colony abundance increased yearly during summer months. Seasonal enhancements varied in magnitude and duration between years. Colony abundance appeared to persist longer than free filaments in some years, increasing even after free filament abundance began to decline, perhaps suggesting aggregation. When Trichodesmium abundance was low, filament length was decreased and colonies were largely absent. Understanding the factors that influence Trichodesmium abundance and morphology is critical for understanding the impact of Trichodesmium on pelagic productivity and nutrient cycling, particularly in quantifying new production.

Presentation Preference: Oral

Primary Presenter: Andrew Hirzel, University of Hawaiʻi at Mānoa (drewhirzel@gmail.com)

Authors:

Andrew Hirzel, University of Hawaiʻi at Mānoa  (ahirzel@hawaii.edu)

Fernanda Henderikx Freitas, University of Hawaiʻi at Mānoa  (fhenderi@hawaii.edu)

Angelicque White, University of Hawaiʻi at Mānoa  (aewhite@hawaii.edu)