Around Heron Island, the inner and outer reef flat zone merge together. Moving from the inner or sandy zone to the outer or living coral zone there is an increase in coral cover with the sandy area often forming channels and pools between the large coral colonies. The outer reef flat zone merges with the boulder zone at the reef edge, which includes the rubble crest. Many sessile animals can be observed encrusting the inner, dead regions of branching coral stands and on the under side of rubble plates. A diversity of gastropods and crabs can be observed in this region, particularly at night.