My first thought upon seeing my very first sea pearl clinging to a reef off the coast of Honduras on my first ever salt water dive was that our dive master was playing another joke. Earlier in the dive, he signaled me to stop at the entrance to a cave while he swam above me shredding an entire loaf of bread. As soon as the bread crumbs began drifting about my head, I found myself in the middle of a huge, disorienting, swirling ball made up of thousands of small fish that had rushed out of the cave.
Now here was the dive master once again, signaling me to stop as he pointed to an orb, approximately the size of a tennis ball, that appeared to be some kind of gazing ball much like the larger ones seen in gardens. I was not going to fall for another of his jokes so I ignored the ball and swam on. Soon I began seeing more of them and decided they might warrant a closer look, given that our fearless leader had no way of carrying that many balls to surreptitiously seed along the reef for the benefit of unsuspecting new divers.
When the dive ended and we were all back onboard the boat, I asked our leader from whence the silvery balls had come, assuming that they were manmade, not naturally-occurring. Jessie advised that they were sea pearls, also known as “sailors’ eyeballs,” an alga from a group commonly called bubble algae. Further research that night revealed that early mariners named this particular bubble algae “sailors’ eyeballs” after peering into the water and seeing what seemed to be eyes peering back at them! Others called it sea pearl due to its resemblance to a fine Tahitian pearl.
The sea pearl or sailor’s eyeball algae are considered the largest of the bubble algae with each of them being a single celled photosynthetic organism; one single cell the size of a tennis ball at their maximum. Ventricaria ventricosa, or Valonia ventricosa, lives only in salt water and is found throughout the Caribbean, north through Florida, south to Brazil, and in the Pacific and Indian Oceans. As with most algae, the sea pearl is green; however, due to the loss of visible coloration as one descends through the water column they can appear to be silver, teal, or even blackish. Generally, sea pearls have a reflective characteristic due to the cellulose structure in the cell walls but they are often covered in other algal species leaving them looking rather whitish and fuzzy.
Not only is the single celled sea pearl the largest of the bubble algae but it is also thought to be one of the largest single-celled organisms in the world. The globe-like body or vesicle, aka the thallus, is anchored to a substrate by minute hair-like appendages called rhizoids that create a surprisingly strong hold. The roundish shape of the sea pearl is maintained by the water-filled thallus.
Due to its size, the large, single celled sea pearl has long been an object of scientific study. According to a report from Cornell University published in Nature, a scientific journal, early studies of the cell walls of mature sea pearl alga produced a wealth of information on cellulose, the main component in the cell walls of alga and plants as well as information on how cell walls develop. As most of us know, plant-sourced celluloid became a key ingredient in plastics, lacquers, synthetic fibers, paper, cardboard, and even gunpowder.
Current studies include the electrophysiology (branch of medicine related to the study of electrical activity in living things) of sea pearls and the unique single celled, multinuclear structure of this macro algae. Perhaps we will one day read that, thanks to the little gazing balls in the sea, science has redefined the accepted definition of a cell…one cell, one nucleus; not so with the sea pearls.
After 30 years as a wild and domestic animal rescuer, rehabber, and educator in the states, Becky Bauer became a scuba instructor and award-winning journalist covering the marine environment in the Caribbean. She is a contributing photographer to NOAA.