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Observations on the development of seaweed communities on concretepanels suspended at three different slope angles – 0° (horizontal),45° (inclined) and 90° (vertical) – were carried out atUranouchi Inlet, Tosa Bay, southern Japan. Each panel had two opposite20 × 20 cm areas, which were affixed with six pieces of 6 × 9 cmacrylic plate on which algal communities were allowed to colonize. The panelswere suspended 1 m below the sea surface from a floating platform fora period of 6 weeks. The experiments were repeated nine times fromAugust 1996 to October 1997. Young thalli could already be recognized on the panels after 3–4 weeks. Thetype of algal community developing on a panel varied with the slope angleas well as the period of suspension. These were classified into the threedominant green algal genera: Ulva, Enteromorpha and Cladophora. The cover and biomass of particular species were clearlyinfluenced by the slope of the substratum.