Microbial biomass and productivity in seagrass beds

Area of Science:

• Marine ecology
• Microbial ecology
• Biogeochemistry

Background:

• Understanding seagrass and bacterial productivity is key to marine ecosystem functioning.
• The nitrogen cycle plays a vital role in coastal environments.

Purpose of the Study:

• To compare seagrass (Zostera capricorni) net production with bacterial production in sediments.
• To investigate interrelationships between these production rates and the nitrogen cycle.
• To evaluate different methods for measuring bacterial production.

Main Methods:

• Seagrass productivity estimated using the plastochrone interval (leaf stapling technique).
• Bacterial productivity measured via tritiated thymidine incorporation into DNA and 32P incorporation into phospholipid.
• Microbial biomass and community structure analyzed using phospholipid techniques.
• Sulfate reduction and methanogenesis rates quantified.

Main Results:

• Seagrass productivity averaged 1.28 g C m-2 day-1; bacterial productivity averaged 33 mg C m-2 day-1 in sediment and 23 mg C m-2 day-1 in water.
• Spatial variability exceeded seasonal variation for both seagrass and bacterial productivity.
• Anaerobic processes predominated in sediments, with strictly anaerobic bacteria being the main microbial components.
• Nitrogen cycling, particularly ammonia turnover, is rapid and likely driven by microbial activity.

Conclusions:

• Bacterial production is a significant component of coastal sediment ecosystems.
• Strictly anaerobic bacteria play a dominant role in the microbial biomass and biogeochemical processes.
• Rapid nitrogen recycling by bacteria and grazers is essential for seagrass productivity.