Stefano Bonaglia examines the experimental sediments at the Askö Laboratory.

Few species colonize the bottom sediments in the Baltic Sea but the ones that occur have important roles and are usually abundant if conditions are favourable. They often provide oxygen to organisms below the sediment surface due to their burrowing and are important for the decomposition of organic material.

Links to eutrophication

Field sampling in the Baltic Sea.

Stefano Bonaglia at the Department of Geological Sciences at Stockholm University and his co-authors have recently published results that indicate that both Marenzelleria, a polychaete that recently colonized the Baltic, and meiofauna, benthic invertebrates < 1 millimetres, affect nitrogen cycling to a much larger extent than earlier believed.

- Even though meiofauna is orders of magnitude more abundant than macrofauna and has a very diverse community structure, its role for mediating nitrogen cycling processes has not been well understood, says Stefano. We have now demonstrated that meiofaunal communities indirectly stimulate microbial denitrification, providing an important ecosystem service that can counteract eutrophication. These results were recently published in the prestigious journal Nature Communications (1).

Another performed experiment showed that the invasive polychaetes Marenzelleria spp. do not stimulate denitrification, as most of infauna organisms generally do (2).

- On the contrary, this species complex enhances dissimilatory nitrate reduction to ammonium (DNRA), a process that leads to retention of nitrogen in the system, Stefano explains. By enhancing DNRA and suppressing denitrification, eutrophication might in fact be stimulated.

For further information
Stefano Bonaglia, Department of Geological Sciences, Stockholm University
Phone: (+46) 8 16 47 96

Volker Brüchert, Department of Geological Sciences, Stockholm University
Phone: (+46) 8 164 7 55


  1. Meiofauna increases bacterial denitrification in marine sediments
  2. Effect of reoxygenation and Marenzelleria spp. bioturbation on Baltic Sea sediment metabolism

Funding programme
Baltic Ecosystem Adaptive Management (BEAM) is a research programme aimed to support ecosystem-based management of the Baltic Sea environment. It combines the University’s successful research on Baltic ecosystems, contaminants, natural resource management and ecological models for environmental management and is part of Stockholm University’s profile area: Climate, Seas and Environment.