High Frequency Multi-Year Variability in Baltic Sea Microbial Plankton Stocks and Activities

Area of Science:

• Marine microbial ecology
• Biogeochemical cycling
• Aquatic microbial ecology

Background:

• Marine bacterioplankton are crucial for global nutrient cycling and organic matter decomposition.
• Previous studies, often using monthly sampling, established the influence of environmental factors on bacterioplankton communities and productivity.
• Fine-scale seasonal microbial activities and their underlying biological drivers remain poorly understood.

Purpose of the Study:

• To investigate the high-frequency temporal dynamics of marine bacterioplankton communities and their activities over four consecutive years in the Baltic Proper.
• To understand the relationships between microbial variables, abiotic factors, and biotic interactions.
• To assess the impact of sampling frequency on capturing microbial dynamics.

Main Methods:

• Conducted four years of high-frequency time-series sampling in the Baltic Proper.
• Measured bacterial heterotrophic production, plankton biomass, extracellular enzyme activities, substrate uptake rate constants (glucose, pyruvate, acetate, amino acids, leucine), and nutrient limitation bioassays.
• Analyzed temporal variations in microbial variables and their correlation with abiotic factors (temperature, nutrients) and biotic factors (phytoplankton blooms).

Main Results:

• Observed pronounced temporal dynamics in most microbial variables, occurring on time scales of days to weeks.
• Bacterial heterotrophic production and abundance increased following diatom, dinoflagellate, and cyanobacterial blooms.
• Substrate uptake rate constants correlated strongly with bacterial productivity, temperature, and cyanobacterial abundance, indicating nutrient limitation influenced microbial processes.

Conclusions:

• High-frequency sampling is essential to capture the rapid temporal dynamics of marine bacterioplankton, which may be missed by lower-resolution sampling.
• Bacterioplankton responses to phytoplankton blooms and nutrient availability are complex and occur on short timescales.
• Understanding these fine-scale microbial dynamics is critical for developing accurate biogeochemical and food web models.