Bubble algae is a bottle green coloured single-celled algae which forms jelly bean or round, marble-like shapes in the marine aquarium. It often starts at the base of corals but can plague if uncontrolled, blocking pumps, weir intake slots and overgrowing corals.
Large growths can be removed by hand but there is one specific critter that reefkeepers use to deal with it. The Emerald Crab, Mithrax sculptus, grows to 2” across and comes from the Caribbean. Like most crabs, it is omnivorous but will also graze algae and importantly, Valonia spp. Bubble Algae.
Look closely and the Emerald crab has spoon-shaped pincers which it uses to grab, pierce and tear the bubbles. They are largely reef safe and the only animal prescribed to deal with Bubble Algae. They are suitable for nano reefs and large reef tanks and for bad manifestations add three or more. Sometimes also available in a reddish colour.
Image credit By Philippe Bourjon – Don de l’auteur, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31572933