Worldwide, abalones tend to be small, in the range of 2 to 4 inches across, according to evolutionary biologist David Lindberg, professor and chair of integrative biology at the University of California, Berkeley, and a former abalone diver himself. Along the California and Pacific Northwest coast, however, abalones have grown much bigger, culminating in the 12-inch diameter red abalone, Haliotis gigantea, avidly sought by divers and once the center of a thriving commercial fishery.
A surge in the last century in the sea otter population, however, killed off the commercial abalone industry along the central and southern California coast and made it hard for sport divers to find any abalones, let alone large, 12-inch ones. Many divers, fishermen and even wildlife biologists worry that the otter is driving the abalone to extinction.
A new study of the interaction between abalones and California's coastal kelp forests, however, suggests that the sea otter played a key role in driving up the size of the abalones. Unlike kelp and algae in tropical waters, kelp in cold waters like those along the California coast have not developed toxic chemicals to ward off voracious grazers like sea urchins and snails. As a result, abalones, which live off the drifting, dead kelp so abundant along the Pacific coast, thrive and grow huge on the highly nutritious food.
The researchers speculate that the sea otter helped set up this state of affairs. By ruthlessly preying on sea urchins and smaller snails, otters kept the herbivores at bay, and the kelp had no need to develop chemical deterrents. Abalones could, for the most part, hide from otters in rock crevices while gorging like couch potatoes on the tasty kelp washed
Contact: Robert Sanders
University of California - Berkeley