Functional group-specific traits drive phytoplankton dynamics in the oligotrophic ocean

Area of Science:

• Marine microbial ecology
• Ocean biogeochemistry
• Phytoplankton physiology

Background:

• Oceanic primary production is largely driven by diverse microbial assemblages.
• Nutrient loading in oligotrophic systems can promote blooms of large eukaryotic phytoplankton.
• Understanding the metabolic traits of bloom-forming phytoplankton is crucial for biogeochemical models.

Purpose of the Study:

• To identify the metabolic basis of functional group-specific traits in eukaryotic phytoplankton.
• To investigate the shift between net heterotrophy and autotrophy in response to nutrient loading.
• To analyze the transcriptional responses of different phytoplankton groups during simulated blooms.

Main Methods:

• Eukaryotic metatranscriptomic analysis was employed.
• Simulated blooms were created by adding deep seawater (DSW) to North Pacific Subtropical Gyre surface waters.
• Transcriptional responses of diatom, haptophyte, and dinoflagellate functional groups were quantified.

Main Results:

• Diatom and haptophyte metabolic fingerprints significantly shifted post-DSW addition, unlike dinoflagellates.
• Differentially abundant genes highlighted co-limitation by nutrients, metals, and vitamins in bloom formation.
• Transcript allocation ratios varied between diatoms and haptophytes, suggesting different growth strategies.

Conclusions:

• Eukaryotic phytoplankton possess metabolic potential for bloom formation, but physical and biogeochemical factors are critical.
• Simulated blooms revealed distinct metabolic responses among phytoplankton groups, indicating varied adaptations.
• Climate change impacts on ocean physics and chemistry may alter phytoplankton bloom dynamics.