Phytoplankton phenology through gene expression during the North Atlantic spring bloom decline

Area of Science:

• Marine ecology
• Ocean biogeochemistry
• Phytoplankton physiology

Background:

• North Atlantic spring bloom phytoplankton dynamics are known, but the physiological drivers and biogeochemical impacts are less understood.
• Phytoplankton metabolism critically influences nutrient cycling, primary production, and carbon export in marine systems.

Purpose of the Study:

• To evaluate relationships between phytoplankton physiology, community structure, and environmental parameters during the North Atlantic spring bloom.
• To understand the role of dominant phytoplankton groups (diatoms, dinoflagellates, haptophytes, chlorophytes) in bloom dynamics and biogeochemistry.

Main Methods:

• Measured phytoplankton biomass, biological rates, and gene expression alongside environmental parameters during a North Atlantic campaign (NASA EXport Processes in the Ocean from RemoTe Sensing).
• Analyzed data to identify relationships within and between four dominant phytoplankton groups.

Main Results:

• Observed a bloom transition from diatom dominance (Phase I) to non-diatom dominance (Phase II).
• Silicic acid depletion limited overall production, reduced diatom competition, and enhanced haptophyte contributions.
• Diatom gene expression for silicon transport was uncoupled from nitrogen assimilation and photosynthesis, indicating altered growth strategies.

Conclusions:

• Variable silicic acid concentrations significantly affect phytoplankton community structure and regulate primary production.
• Silicic acid availability plays a key role in the decline of the North Atlantic spring bloom and influences carbon export pathways.