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Blade runner stalks rocky reefs

Recent flat conditions make for sublime snorkeling, swimming and diving explorations, water temperatures not withstanding. The place to visit is the submerged shallow rocky reef habitat of the La Jolla Ecological Reserve.

Enter either from La Jolla Cove or La Jolla Shores, because the reef extends the length from one entrance to the other. From the Cove, take one step into the water and you’re there. At the Shores, you’ll need to access the leafy-covered substrate from the Marine Room.

From under water, the labyrinth of submerged rocks and boulders are evidence that the cliffs above won’t stand forever. Those who resist change may lament the erosion above the waterline, but the underwater world benefits from the fallout. The boulders themselves may not be alive like corals that make up a tropical reef but for both, the habitat that is formed attracts myriad life.

The giant kelp (Macrocystis pyrifera) prefers anchoring a bit further out, but the shorter, tougher algal species prevail in the rocky arena abutting the cliffs, caves and shore. This setting attracts various red, brown and green plant and plantlike growth. The lush foliage provides an inviting foundation that attracts other life to come and stay.

One resident ideally suited to make a home here is the giant kelpfish (Heterostichus rostratus). With a sharp, pointed snout and forked tail, giant kelpfish are impossible to mistake for other local fish — that is, if you can find one. Though relatively abundant, many long-time divers have never laid eyes on one of these stealth beauties because they travel solo and masterfully blend into their background using a variety of disguises. Females may be red, brown or green (like the foliage) and grow to more than a foot long. Males top out at about a half-foot long and can’t muster colors beyond brown to olive-green. Both sexes may add stripes, bars or mottling, whatever best matches their immediate surroundings or emotions. Be they patterned or plain, as an added cloaking device the giant kelpfish body is flattened and elongated to mirror the shape of the weedy blades. Further, giant kelpfish orient themselves to the angle of the fronds and sway in rhythm with the surge, just like their algal alter egos.

Kelpfish spawn year-round, but spring is high season. Each male safeguards his nest of algae to which a female lays eggs that sport entangling threads for adhesion. Males remain vigilant for a couple of weeks until the eggs hatch. The resulting larvae drift in the sea soup for another couple of weeks, then juvenile kelpfish settle, especially around the giant kelp fronds, schooling with others of their size and ilk while feeding on tiny crustaceans.

Kelpfish coloration follows development. Half-inch-long youngsters are transparent, and inch-long ones are amber-colored with white blotches. Unlike adults, juveniles remain in clear view within the kelp canopy, but once they grow to a couple of inches long, they descend deeper and go it alone. This makes sense, because hanging out with others would likely sabotage the many traits that allow these fish to hide in plain sight.

If I were to choose a favorite fish, it might be the giant kelpfish, and not because they are challenging to find. Each is like a snowflake or fingerprint because no two are identically colored and patterned. Every sighting, then, is a surprise, because I have no idea what one-of-a-kind outfit any giant kelpfish will be wearing. Au couture!

— 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 jgarfield@ucsd.edu.