Description

Also known as Brittle-disc Seaweed, Coralline Algae, Green Algae, Green Siphonous Algae, Marine Algae, Prostrate Sea Cactus, Watercress Algae.

Found in clumps attached to the substrate, around dead corals, mangroves, and seagrass beds, of shallow lagoons, coral and rocky reefs.
Length - 17cm
Depth - 0-25m
Widespread Atlantic Ocean, Mediterranean, Indo-Pacific

As many as 9000 species of algae are spread across the worlds oceans, some can be as much as 30 metres across while others are just a slippery scum over rocks.
Algae grows wherever there is enough light and life supporting conditions.
They support a huge number of marine life both for food and as a home. (edit) Ref: https://www.sealifebase.ca/summary/Halimeda-opuntia.html