Sand flats
Subtidal sandflats cover a large area of the Cook Island Aquatic Reserve, extending from the shallow reef around the island out to the deepest parts of the reserve.
Close to the rocky reef, the sediment comprises a mixture of coral rubble, small rocks and sand. With increased distance from the island the sand grains become finer and more uniform.
Marine life
Differences in sediment across the aquatic reserve support a variety of invertebrate and marine plant communities that live on or within the sediment. Invertebrates include molluscs (e.g. snails and bivalves), worms, and crustaceans.
Fish feeding on these invertebrates include whiting, goatfish, tarwhine, trevally, crested morwong, eagle rays, and bluespotted maskrays.
Larger invertebrates like sea cucumbers, sea stars and brittle stars are also found on the sand flats. Sea cucumbers feed on the sand and break down the tiny particles of algae, microscopic organisms and detritus, excreting clean sand and helping to recycle nutrients as they go.
Various species of sharks and rays, like leopard sharks, and grey carpet sharks, can often be seen resting on the sandy bottom near the reef.
The sand flats also provide a place for seagrasses and some species of macroalgae to grow.
Leopard shark resting on sand flats
(Photo: Rudi Vir)
Swift-footed hermit crab camouflaged with algae, sand and shell grit on its shell
(Photo: Rudi Vir)
Giant Queensland grouper, a protected fish in NSW, cruising over the sand flats (Photo: Leigh Edwards)
Holothuria sea cucumber and Guilding’s sea star on the edge of the sand flats (Photo: Ecological Service Professionals)
