Halimeda green algae (Halimeda cuneata). A large amount of almost white sand is associated with coral reefs, some being produced by Halimeda algae.

One of the most ubiquitous of these sand-producing plants is this green leafy alga which deposits granular calcium carbonate in its tissues. When the plant dies (the dead areas appear white), the decayed grains fall free as instant sand. Among the many tropical species of Halimeda, this is the only one known to reach the southern Australian coast.