Impact of Biodeposition on Macrofaunal Communities in Intertidal Sandflats

Abstract

Abstract. This investigation deals with the changes in macrofaunal communities in intertidal sandflats caused by the input of organic material via biodeposition produced by mussel beds. The area of investigation was the back barrier tidal flat system behind the East Frisian Island of Spiekeroog. Due to erosion by the ebb current a plume of biodeposits extended from an area of mussel beds (Mytilus edulis) towards the adjacent sandy sediments. This plume represented a gradient of decreasing contents of organic material. Five stations were installed along this gradient to analyse the effects of this organic input on the macrofaunal communities; a control station was placed on sandy sediments.The macrofaunal communities differed along the transect. In the mussel patches oligochaetes dominated, whereas deposit‐feeding polychaetes increased along the transect. These polychaetes were different from the communities of the sand flats. The changes in the macrofaunal communities discussed in the framework of the organic carbon contents of sediments and interspecific relationships.After a cover of green algae during summer and after a cold winter, the mussels were almost completely eliminated from the area of investigation and reaggregated in another area of the flat. The layer of biodeposits eroded as well. After the decrease in contents of organic matter, the macrofaunal communities no longer followed the transitional distribution but showed a diffuse and seasonally influenced distribution.The results indicate that biodeposits changed the quality of the sediment structure of the sand flats and that the amount of organic matter (TOC) is a main structuring factor for the macrofaunal communities.