Informing and inspiring everyone about California’s underwater world

All Columns

Reflections on a painted cave_Sydney's Ocean Log

Another day dawns hot and muggy, and here I am in my fur coat all dressed up and ready for saltwater lubrication. Truth be told, I’m not much into car rides but when they're brief and end with the waves lapping at my ankles, I’m in. Flat sea conditions settled the decision to explore La Jolla’s sea caves. My faithful companion and I bellied up to the hollow openings to ooh and aah at the lavender- and pink-doused rocks and boulders. This is the life. Nature sure got passionate with buckets of paint.

Crustose coralline algae grow very slowly because the process that makes these algae hard (calcification by calcium carbonate) takes a lot of energy. © I know the colors coating the rock walls and undersea boulders don’t look alive but they are. Called red algae, specifically coralline algae, and more specifically, crustose (crusty) coralline algae, the plantlike photosynthesizers are as hard and brittle as the most disappointed human you’ve met. While these stonelike algae do not build skyscraper forests in the sea like giant amber kelp, they may still span impressive lateral acreage, although their crusts are less than skin deep. And you can’t beat (or should I say beet) the pigment for drama. But the color is lavender, not beet red, you bark. First off, leave the barking to me and know that crusty red algae can also be lavender or pink.

We aren’t the only ones to have crustose reds in our coastal midst. Tropical corals share a close-knit relationship with these algae. Of course, algae can’t be coral kin because corals are animals and algae just aren’t. Still, both make the hard stuff, calcium carbonate, which brings us to the “reef” in coral reef. Corals couldn’t construct reefs without their trusty crusty-red partners. Living coral animals can only make the bricks of the reefs. They do so by extracting calcium and carbonate from the water and then building it into their skeletons. However, as every mason knows, bricks alone do not hold a structure together; you need mortar, too.

Enter the cement of the reef, stonelike red algae, which deposit calcium carbonate in their cell walls. Tropical red algal species spread over and fill gaps between the coral "bricks," thus gluing together the whole shebang. It’s not fair that corals get all the credit in the name of coral reefs, when crusty reds majorly subsidize corals’ activities. We should pay homage to these thankless underdogs of the reef and more rightfully call them algal reefs. Like that’s ever gonna happen. 

Snail shells are rocklike and make great settle-down spots for crusty red algae. ©www.TideLines.orgLa Jolla’s cave walls are not the only painted surfaces. A slew of snails, invisible to me at first, had their shells identically tint-tagged by the algal graffiti artists. It must be a muddle for snail predators to find such prey. It’d be like trying to separate a Samoyed from a snowstorm. Stony reds themselves don’t much worry about predators because not many grazers like munching on the equivalent of marble. Still, as substrate, these algae roll out their crusty welcome mat to the wider community, especially juvenile invertebrates. In fact, encrusting red algae are the hosts with the most—species that is—compared to areas where no such algae live.

When crustose coralline algae die, they bleach to snow-white just like corals. ©www.TideLines.orgCrusty reds look and feel stone solid but they face a formidable foe: warming of the ocean from climate change. Like corals, crustose algae may be weakened by long, warm spells in the sea. I see dead, encrusted reds here and there in my swim travels; they bleach just like corals do. Scientists are now bending their brains to the problems facing the many species of crustose coralline algae. I hope these stone-coating reds keep being a part of the ocean's future. No one can take their place, and they do a heck of a paint job on cave interiors.


Sydney the Golden Seal is a retriever-husky who has logged miles of ocean swims. She writes her column, “Sydney’s Ocean Log,” about the wonders of our watery world. When not dog paddling or opining, Sydney pursues archaeology research in her backyard. Write to Sydney using the Contact page, and put Sydney the Golden Seal in the Subject line.


— Judith Lea Garfield, naturalist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. Send comments to