They might be a kind of cyanobacteria called nostoc that sometime grows in round balls.
From the image, it would seem to be bubble algae. According to Wikipedia,
Valonia ventricosa, also known as "bubble algae" and "sailors’ eyeballs," is a species of algae found in oceans throughout the world in tropical and subtropical regions. It is one of the largest single-cell organisms.
Valonia ventricosa typically grow individually, but in rare cases they can grow in groups. They appear in tidal zones of tropical and subtropical areas, like the Caribbean, north through Florida, south to Brazil, and in the Indo-Pacific.Overall, they inhabit virtually every ocean throughout the world, often living in coral rubble. The single-cell organism has forms ranging from spherical to ovoid, and the color varies from grass green to dark green, although in water they may appear to be silver, teal, or even blackish. This is determined by the quantity of chloroplasts of the specimen. The surface of the cell shines like glass.
Credit:stackoverflow.com‘