Algea ID. Stiff/hard, growing in balls on sand and hard to remove from rock

[Mike-sk]

Does anybody know what algae this is?

 

[ISpeakForTheSeas]

Welcome to Reef2Reef!

The below would be my best guess at this point:

Possibly a Lychaete sp.? For example:

Lychaete herpestica Filamentous Green Algae

Lychaete herpesticais commonly referred to as Filamentous Green Algae. Difficulty in the aquarium: Not suitable for aquarium keeping. Toxicity: Toxic hazard unknown.

www.reeflex.net

If not, I'd lean toward it being something else from that family (Cladophoraceae), as the bubble tubes are pretty unique - they're too long to be Valonia or similar, and too translucent to be Codium.

Edit: To show another, similar-looking member of the family:

Luxuriant Cladophora, Cladophora catenata