Following the reef flat is a vertical
drop-off of 3-6 meters which leads to the main Puako reef. This is area of caves and crevices
filled with encrusting corals and sponges. Tube corals (Tubastraea
coccinea), best observed at night, cover many of the walls
creating orange carpets. Other corals, such as species of the
genus Leptoseris and Pavona, are also common. Black
sea urchins, mainly Echinothrix diadema and E. calamaris,
are common in holes on the walls. Green sea turtles (Chelonia
midas) are commonly found sleeping in caves. This threatened species feeds
on seaweeds growing on the vertical cliffs and reef flat,
especially members of the red seaweed genus Pterocladia.
Turtles are also commonly seen sleeping in depressions on the
main reef and gracefully swimming over the bottom. Schools of
small fish may occasionally be seen feeding off the seaweeds and
encrusting invertebrates on the backs of green sea turtles.