Marine heatwaves and optimal temperatures for microbial assemblage activity

Area of Science:

• Marine microbiology
• Biogeochemistry
• Oceanography

Background:

• Microbial assemblages play a crucial role in marine biogeochemical processes.
• Understanding microbial responses to temperature is vital, especially in the context of climate change.
• Seasonal variations in coastal water temperatures influence microbial community dynamics.

Purpose of the Study:

• To investigate the response of microbial assemblages to instantaneous temperature changes in the western English Channel.
• To determine seasonal patterns in bacterial abundance and temperature optima.
• To assess the potential impact of rising sea surface temperatures and marine heatwaves on microbial activity.

Main Methods:

• Seasonal sampling over 13 months (November 1999-December 2000).
• Measurement of bacterial abundance via 3H-leucine incorporation across a temperature gradient (5°C to 38°C).
• Calculation of Q10 values and determination of optimal assemblage temperature (Topt).

Main Results:

• Bacterial Q10 values exhibited seasonal variation, with higher values (>3) in autumn compared to spring and summer (around 2).
• The optimal temperature for microbial assemblages (Topt) showed a seasonal pattern, often out of phase with sea surface temperature.
• In winter, Topt was significantly higher (approx. 20°C) than ambient sea surface temperature, while in summer, it was only slightly higher (2.8°C).

Conclusions:

• Discrete periods of anomalously high sea surface temperatures may approach or surpass temperatures critical for maximum microbial activity.
• Increasing frequency and intensity of marine heatwaves due to climate change could significantly alter microbial assemblage function.
• Changes in microbial activity under extreme temperatures may have profound implications for marine biogeochemical processes.