Sea Pearl Algae – A Species Spotlight

Round and glassy-looking, a sea pearl photographed at Curacao.

IF IT LOOKS LIKE A RUBBER BALL AND IT FEELS LIKE A RUBBER BALL, IT MUST BE…ALGAE, a version commonly called a sea pearl (Ventricaria ventricosa). Sea pearl algae is an occasional reef denizen found worldwide that stands out because it so often looks like a delicate glass ball.

Typically about the size of a golf ball, sea pearls are remarkable for their structure. Each one is a single cell, all by itself. Its round, glassy oddness also means that sometimes it’s nicknamed the “sailor’s eyeball.” Also, “bubble algae.” Also Valonia ventricosa.


Sea pearls don’t actually do much. Actually, they don’t do anything beyond lying around tucked into various sheltered spots on the reef. You may see several of them together from time to time, but typically, they’re solitary.

They’re found on the reefs, in seagrass beds, on the roots in mangrove groves – anywhere they can find a solid substrate. They’re attached to their hard settings by hair-like rhizoids, or runners.


The shape of sea pearl algae can vary from round to oblong. They’re usually green, often dark green. As algal cells, they have chloroplasts, specialized compartments that perform photosynthesis, and the number of chloroplasts affects their degree of green color.

On the other hand, underwater they can look more silvery and glassy. This may reflect the fact that they’re often covered with thin, silvery to light lavender algae. They reproduce by cell division.

Sea pearl algae can take an oblong, or egg, shape.
Sometimes V. ventricosa takes an oblong shape.


Because of their single cell size and unusual internal structures, sea pearl algae have been studied in laboratories a lot. For one thing, cellulose fibers in their cell walls are formed in unusual patterns for a cellular structure – parallel, crossing and swirling. They’re been studied for their osmosis capabilities – they don’t seem to have any pores for stuff to pass through – and for their high electrical potential versus surrounding seawater.


A single cell of algae probably should be called an alga. But that sounds weird, if technically accurate. For one thing, doesn’t even have a separate entry for alga. For another, it’s relatively unusual to encounter solitary alga cells, so you’re always talking about algae.  As a result, here, it’s an algae, single cell or not.

PRINCIPAL SOURCES: “Sea Pearl,” Reef Coral Identification, Florida, Caribbean, Bahamas, Paul Humann, Ned DeLoach;  Sea Pearl, Marine Species Identification Portal; “Sea Perl,” Florent’s Guide To The Florida, Bahamas & Caribbean Reefs; Valonia ventricosa,”