The seaward platform is the outer portion of the reef edge that gently slopes and merges with the reef slope. It typically is lacking in loose coral rubble and often has a high amount of living coral cover; other areas are cemented by encrusting coralline algae. On the southern side of Heron Island Reef this zone is exposed to the prevailing southeast swell and dominated by massive and tight-branching corals. On the northside, plate corals are more dominant.