SEASONALITY OF PLANKTONIC PROKARYOTES FROM SURFACE WATERS TO THE SEAFLOOR IN THE NORTH PACIFIC SUBTROPICAL GYRE

Documenting the seasonal cycles as well as stochastic environmental responses of open ocean marine prokaryotes can assist in assessing how environmental change may impact microbial communities and ocean ecosystem processes. We report here on the seasonality of open ocean suspended prokaryotes in high resolution depth profiles (5 m to 4000 m) over 8.5 years in the North Pacific Subtropical Gyre at Station ALOHA. In the upper water column (>150 m), recurrent annual periodicity was observed across the entire microbial community, with 69.4% of individual bacterial and archaeal taxa exhibiting robust annual cycles.  Prochlorococcus variants dominated the annually periodic prokaryotes in surface waters in winter, while the majority of their annual maxima shifted to spring and summer in the subsurface of the photic zone. Surface water heterotrophs dominated the annually periodic prokaryote taxa that peaked in spring, summer and fall. Subsurface photic zone winter and fall maxima were dominated by heterotrophs and chemolithoautotrophs. This may be due to decreased photon fluxes in fall and winter, accompanied by decreased photoautotroph abundances and less competition for macronutrients in these seasons and depths.  Notably, although the number of taxa exhibiting annual cycles diminished at depths below 150 m, some bacteria and archaea at meso- and bathypelagic depths also displayed robust annual periodicities. Specifically, the percentage of total prokaryote taxa displaying significant annual periodicity at depths of 1000 m, 2000 m, 3000 m and 4000 m, were 11.6%, 7.5%, 11.1% and 2.8% respectively. Some annually periodic taxa recovered from deeper waters actually originated from the surface, presumably reflecting recurrent annual cycles of export. Most annually cycling taxa recovered in deep sea samples, however, were autochtonous in origin. Our study provides new perspective on the seasonality of suspended planktonic prokaryotes throughout the open ocean water column, and how these microbial communities respond to variable ocean ecosystem processes and climate change.

Presentation Preference: Oral

Primary Presenter: Fuyan Li, C-MORE, University of Hawaii at Manoa (fuyanli@hawaii.edu)

Authors:

Fuyan Li, Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai‘i at Mānoa, Honolulu, HI, USA  (fuyanli@hawaii.edu)

Andrew Burger, Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai‘i at Mānoa, Honolulu, HI, USA  (aburger@hawaii.edu)

John Eppley, Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai‘i at Mānoa, Honolulu, HI, USA  (jmeppley@hawaii.edu)

Edward DeLong, Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawai‘i at Mānoa, Honolulu, HI, USA  (edelong@hawaii.edu)