A coral reef rivals even a rainforest for its diversity of life. Built by tiny creatures, less than half of 1% of the sea floor is covered with coral reef, yet it can support a quarter of all marine species. Some coral reefs are found in areas where food is scarce, so the creatures that live here have had to adopt a different and highly specialised way go get enough food. From large fan-like arms which collect plankton, to sticky arms and even cannibalism, all are useful attributes and strategies to help something gather a nourishing scrap. Porcelain crabs have a fan of filaments on their front legs; a boxer crab attaches a tiny sea anenome on each fist using its sticky tentacles to gather passing plankton. A orangutan crab is coated entirely with sticky hairs. A sea cucumber uses its tentacles to grab food from the sediment. There are hunters too, like the sea slugs. Their vibrant colours are a warning that they're toxic. There are over 3,000 species of sea slug, many of which hunt only one thing and some of which hunt each other.