Impact of polychaete infauna on enzymatic protein degradation in marine sediments affected by intensive milkfish farming

Marine sediments at intensive fish farming sites in Bolinao-Anda, northwestern Philippines, are characterized by strong oxygen depletion and the widespread predominance of sulphidic conditions precluding macrobenthic infauna. In less affected areas, however, small macrobenthos (Spionide polychaetes) was present. Experimental sediment mesocosms containing burrowing polychaetes were set up to investigate the possible links between macrofaunal bioturbation of the sediment and its proteolytic capacity to recycle protein-rich fish farming waste. Relative to polychaete-free sediment, the addition of small Spionide polychaetes had no significant effect on the proteolytic capacity but caused an increase in the redox potential. On the other hand, the addition of large Eunicide polychaetes caused an increase in both the proteolytic capacity and the redox potential. The deposition of commercial fish feed particles increased the proteolytic activities but decreased the redox potential particularly at a higher deposition rate (250 g m-2 day-1). Accumulation of hydrogen sulphide increased at deposition rates above 83 g m-2 day-1 and limited the survival of large polychaetes.