The La Jolla submarine canyon is rife with life but the California sea hare (Aplysia californica) surely wins the award for stand-out species of this past summer. Divers could not miss their large numbers (in the hundreds), size (more than a foot long), and singular activity (unrestrained orgies). The moniker “sea hare” is both a nod to the curled tentacles atop the head, called rhinophores, which resemble rabbit ears, and the overall body shape, which mirrors a crouching rabbit. Soft-bodied with a muscular foot that nearly covers the entire underside, a sea hare moves its mottled, wine-hued body in inchworm-like fashion along the seafloor. Pinpoint-sized black eyes, invisible to all but the highly observant, dot the base of the head’s rhinophores, but a sea hare only senses light from them. Instead of vision as we know it, sea hare eyes are used as a 12-hour clock to synchronize the body’s biological rhythms. Thus, a hare’s real vision, as it were, is left to the rhinophores and pair of large tentacles at the front of the head, two sensory organs that allow the hare to easily find food, detect danger and meet up with others of its ilk. A sea hare changes food sources as it grows. Though a permanent herbivore, it targets red algae when first settling out of the plankton, not only to derive nutrition but also to absorb the pigments that achieve its purple presence. After gradually moving closer to shore, brown and green algae broaden the diet. Not a food fuss, if a preferred algal species isn’t available, a sea hare makes do from what is. The sea hare emigration from greater canyon depths is blatantly apparent. As if responding to a fire drill, groups of hares march (albeit at a snail’s pace) together toward shallower depths, all identically oriented, until they reach their spawning destination. There they cling together in close-knit aggregations of up to 30 individuals from my count. A sea hare is hermaphroditic, meaning it carries both male and female reproductive parts. Mating sea hares may look haphazardly glommed onto each other but they know their roles, which change when each sea hare alternates being male and female on different days. The eggs are fertilized from a sperm storage chamber just before they are laid in long, tangled, yellow strings. While I see some hares mating in pairs, “the more the merrier” approach holds sway. Mating continues for several hours, followed by an hour or more of egg laying. I’ve revisited clumps of mating hares over multiple days and no one appears to have moved, even for a snack break. Only fresh, yellow spaghetti harboring millions of embryos continues to spill out and under the mounds of bodies. Aside from this seasonal, mesmerizing spectacle, a sea hare’s dark, squishy frame and sleepwalker stride typically garner yawns from most divers. Not so Eric Kandel, who must be a lifetime fan. In 2000, the Columbia University professor was awarded a Nobel Prize in Physiology or Medicine for his research on Aplysia. The groundbreaking work led to a basic understanding of how learning and memory take place, and also shed light on how psychoactive drugs and medications are processed at the cellular level. Why he chose Aplysia as his model is quite simple, literally. The hare’s unique physical properties (such as a gigantic neuron) and simply organized nervous system (such as having only a few neurons) make the animal a one-of-a-kind model ideally suited for neuroscience studies. With our billions of neurons, humans are far too complex to study, but because we evolved from simpler organisms like the sea hare, scientists study it to learn about basic processes. You could say that we are the fully loaded model while a sea hare is the stripped-down version. Studying this animal then means much more than merely understanding the workings of a sea hare nervous system (though nothing wrong with that). Insights gained from such work translate into understanding how other organisms, like us, operate. The California sea hare is both a model neuroscience subject and a sea critter intrinsically valuable to the marine ecosystem. Moreover, at the right time of year in our part of the world’s ocean, a fascinating true-life drama unfolds, rewarding intrepid scuba divers with an opportunity to closely observe an otherwise stealth animal in its natural habitat and in the midst of a most important job — assuring its continued survival as a species. — Judith Lea Garfield, biologist and underwater photographer, has authored two natural history books about the underwater park off La Jolla Cove and La Jolla Shores. www.judith.garfield.org. Questions, comments or suggestions? Email [email protected].