Bubbles on crab shell?

Never seen this before. Hermit crazy has maybe 10 bubbles on its shell. Thanks in advance for any advice.

Those are bubble algae, algae in the genus Valonia. Not a lot of animals eat them.

Agree. Looksd like bubble algae. Many will take it out and scrub it off then put the crab back.

Thank you! How does that happen when there’s no bubble algae in tank?

The way I understand it isn’t only takes one spore. Can come in on shells, rocks, coral, etc.

Bubble algae can come on the rock or hard shell of animals, or spores in water. It grows due to nutrient problem. some of these species do not require a great deal of light. Essentially it is likely to be in your aquarium even if it is not visible to the naked eye. Best way to manage it is to keep your nutrients in check. Normally it cause no problem. Interesting corals, conversational plant in the tank.