The importance of fouling the harbour of Ostend in 1964

1. Frames with slides of different nature were submerged in the harbour of Ostend, Belgium, on the first of June 1964, to detect qualitative and quantitative differences in their fouling. 2. After two months the devices were covered with a black mud-layer of several centimeters in thickness, which made a detailed analysis of the slides impossible. 3. Examination of this mud revealed that the tubulous polychaete Polydora ciliata (Johnston) was the primary cause of this enormous overgrowth. 4. A list of the species found in the mud is given