Artificial reefs are very effective devices for attracting and supporting large populations of fish. They can provide complex, hard surface habitat in areas where only soft bottoms occur, which includes much of Hong Kong waters. Large artificial reef structures also provide improved feeding opportunities for many fish by changing water flow patterns. Localised areas of high flow are created as moving water passes over and around large artificial reef structures and low flows are established in sheltered areas inside the structure and at the downstream side. High current flows attract plankton feeding fish and their predators. Artificial reefs also provide good opportunities for planktonic fouling organisms to settle and develop. These fouling organisms, which include polychaetes, barnacles and mussels, flourish on artificial reefs and attract many predators, such as crabs, shrimps and fish, to feed and be fed. Artificial reefs create new and complex food webs in areas that are habitat-limiting.