Phytoplankton competition and resilience under fluctuating temperature

Area of Science:

• Marine ecology
• Phytoplankton dynamics
• Environmental variability

Background:

• Environmental variability complicates predictions of species interactions.
• Non-linear responses of species to abiotic factors hinder accurate predictions.
• Influence of thermal fluctuations on phytoplankton growth and competition is largely unknown.

Purpose of the Study:

• Investigate the limits of coexistence in variable environments.
• Determine the impact of temperature fluctuations on marine diatom competition.
• Assess the role of nitrogen availability in modulating responses to thermal variability.

Main Methods:

• Stable mixed cultures of *Phaeodactylum tricornutum* and *Thalassiosira pseudonana* were used.
• Cultures were exposed to 17 different temperature fluctuation regimes.
• Experiments were conducted under both high and low nitrogen conditions.

Main Results:

• Phytoplankton demonstrated significant resilience to temperature variability.
• Coexistence disruption occurred at high temperature fluctuation amplitudes (±8.2°C) under high nitrogen.
• Nitrogen limitation lowered the disruption threshold to ±5.9°C.
• Species exhibited differential recovery rates from temperature fluctuations.

Conclusions:

• Environmental cycles can reduce species replacement rates below certain fluctuation thresholds.
• Above these thresholds, competitive exclusion may accelerate, impacting phytoplankton communities.
• Aquatic heatwaves and nitrogen availability can drive abrupt community restructuring.