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The straight scoop on kelp curlers

If I had eight pairs of limbs, I’m certain I’d be constantly in knots. Fortunately amphipods — small, shrimplike crustaceans with said number of limbs — intrinsically know what pairs of limbs to use when and where. Ampithoe humeralis, commonly called a kelp curler, measure about 1 inch long. The package is made up of a j-shaped body, which is flattened from side to side, an oval head from which two super-long antennae spout, and lots of limbs.

Deciphering the jobs of the limbs is easier described than visually untangled. The pair closest to the head are short and fused at the base. They act as mouth parts. The longer and larger second and third limb pairs have pincerlike structures to gather food. The lower six limb pairs are all about mobility. Though not specially accessorized, these limbs are unique to other crustacea in the way the pairs are arranged: The first three pairs are adapted for swimming, and the three pair below them permit walking and jumping.

A kelp curler’s world revolves around kelp. Found throughout the giant kelp (Macrocystis pyrifera) forests of California, the herbivorous curler not only depends on the seaweed for food but lodging as well.

The blueprint for kelp curler home construction is simplicity at its best. First, choose a healthy leaflike kelp frond; second, lie down on the blade and pull one end of the frond over lengthwise until it touches the frond’s other edge: third, “sew” together the curled frond with sticky homemade threads (a gluey substance) often referred to as “amphipod silk.” The resulting domicile loosely resembles a pea pod and is variable in size. Often, the hollow interior can be quite roomy, a plus for any female protecting a growing brood. Yet, a kelp curler isn’t a prisoner of its dwelling because both ends of the pod have a small opening to permit comings and goings.

I’ve rarely seen a kelp curler out in the open because if it’s not cloistered in its jury-rigged kelp shanty, having near transparency makes for an ideal camouflage. Recently, I discovered lots of kelp curlers in folded-over giant kelp fronds off of La Jolla Shores. I watched how a curler leaves its home, first by sampling the great outdoors with long sensory tentacles to assure the coast is clear, then zipping out like a shot. They are fast movers as they race and hop from one frond to another. If what I describe sounds like paranoid behavior, I’d act the same way if I were a kelp curler because amphipods are on the menu of most any small fish and many other invertebrates.

In general, curlers don’t bite the hand that feeds them. Usually there aren’t enough kelp curlers to seriously damage the host plant with all the population checks in place, but the crustaceans can overgraze if there are enough of them and the kelp is otherwise weakened. As far as impacts to kelp from curler home construction, studies in other Macrocystis and kelp curler species show that a kelp frond continues growing, albeit slower. The first three rules in real estate don’t seem to apply to curlers because I find them (or their abandoned lairs) at all depths along a vertical kelp stand (from about 60 feet deep to the surface), which makes sense since every view is oceanfront.

As with most noncommercially important species, a kelp curler’s role in the health and stability of a kelp forest community is poorly understood. This is concerning because, for example, we can’t finely manage commercially important fish stocks like yellowtail, which are closer to the top of the food web, if we are ignorant of what’s going on at the lower reaches of the food chain. If this food chain were a building, yellowtail would be part of the roof. Amphipods, being near the bottom of the food chain, make up part of a building’s foundation. Here’s why: many other fish rely on amphipods for part of their diet, and those fish are themselves preyed upon by other fish species, and so on, until a fish distantly connected to the kelp curler is scarfed down by a hungry yellowtail. No doubt, a solid, stable foundation supports the rest of any structure. Fisheries management via single species is finally beginning to go the way of the dinosaur, having lost favor to the modern strategy of ecosystem-based management, which includes marine protected areas. I hope greater effort will be put toward understanding critters like the kelp curler, because the health of the kelp ecosystem, and the ocean ecosystem at large, rests to some degree on the shoulders of these small, secretive and silent partners.


— 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