Light-driven synchrony of Prochlorococcus growth and mortality in the subtropical Pacific gyre

Francois Ribalet, , Sophie Clayton, Valeria Jiménez, Sebastian Sudek, Yajuan Lin, Zackary I. Johnson, Alexandra Z. Worden, E. Virginia Armbrust
June 2015
PDF Cite DOI

Abstract

Theoretical studies predict that competition for limited resources reduces biodiversity to the point of ecological instability, whereas strong predator/prey interactions enhance the number of coexisting species and limit fluctuations in abundances. In open ocean ecosystems, competition for low availability of essential nutrients results in relatively few abundant microbial species. The remarkable stability in overall cell abundance of the dominant photosynthetic cyanobacterium Prochlorococcus is assumed to reflect a simple food web structure strongly controlled by grazers and/or viruses. This hypothesized link between stability and ecological interactions, however, has been difficult to test with open ocean microbes because sampling methods commonly have poor temporal and spatial resolution. Here we use continuous techniques on two different winter-time cruises to show that Prochlorococcus cell production and mortality rates are tightly synchronized to the day/night cycle across the subtropical Pacific Ocean. In warmer waters, we observed harmonic oscillations in cell production and mortality rates, with a peak in mortality rate consistently occurring ∼6 h after the peak in cell production. Essentially no cell mortality was observed during daylight. Our results are best explained as a synchronized two-component trophic interaction with the per-capita rates of Prochlorococcus consumption driven either directly by the day/night cycle or indirectly by Prochlorococcus cell production. Light-driven synchrony of food web dynamics in which most of the newly produced Prochlorococcus cells are consumed each night likely enforces ecosystem stability across vast expanses of the open ocean.

Type
2
Publication
Proceedings of the National Academy of Sciences
Cell Division Cyanobacteria Flow Cytometry Mortality SeaFlow
Francois Ribalet
Francois Ribalet
Research Associate Professor

Our work combines high-resolution ocean observations and statistical modeling to reveal how environmental changes affect the growth of marine microbial communities, helping us understand their role in marine ecosystems and global carbon cycling.

Senior Research Engineer

I develop new instrumentation to study the complex structure of microbial communities in the oceans. My work spans the fields of optical, mechanical, software and electrical/electronic engineering. Instruments such as the SeaFlow sheathless flow cytometer are designed and built from the ground up in my laboratory and machine shop. SeaFlow is currently being operated monthly on Hawaii Ocean Time-Series cruises and annual SCOPE funded cruises. I am currently working on a new flow cytometer for autonomous platforms. This cytometer, named PipeCyte, uses an immersion primary optic combined with sheathless detection optics to perform in situ single cell measurements in any fluid scaled to any size. The first target platform will be on board a CTD to perform continuous depth profiles of the phytoplankton community.