ROBUST: The role of buffering capacities in stabilising coastal lagoon ecosystems

The main information about Robust project:

During the running of the ROBUST projects so-called "Buffer capacities" has been defined in ecology as a holistic concept, but it also turn out that it can also be worked in several mechanistic studies. The concept of "buffering capacities" was applied to understand the limited "local stability" in seagrass ecosystems and their vulnerability towards structural changes into macro-algal dominated communities.

The following processes and studied were explored and it realized that they could confer buffering capacities to the seagrass ecosystem:

• net autotrophy was persistent in Zostera noltli meadows where plant assimilation acts as a sink for nutrients, this contrasted with the Ulva system that shifted back and forth between net autotrophy and net heterotrophy
• the Zostera noltii ecosystem possesses a certain albeit rather limited capacity to modify the balance between nitrogen fixation and denitrification, ( it was found that in situ nitrogen fixation always exceeded denitrification)
• the nitrogen demand of organoheterotrophic bacteria in the sediment results in nitrogen retention of N in the sediment and hence a buffer against release of nitrogen compounds from sediments
• habitat diversification in seagrass meadows provided shelter for meiofauna and hence buffering against adverse conditions sedimentary iron provides a buffer against noxious sulfide (note: bacterial sulfide production is enhanced in anoxic sediment niches by increased organic matter loading).
  

On the other hand, in the ROBUST project the coastal system were studied, sedimentary iron appears less important as a redox-coupled buffer system against phosphate loading. This is because most inorganic phosphate is bound to calcium rather than to iron. In addition, our studies have highlighted the importance of plant-microbe interactions in the seagrass meadows.