Common life forms include clams, abalone, limpets, chitons, hermit crabs and flower-like anemones. Tiny worms build huge honeycomb homes on shallow rocky ledges. Nutrients from seal and sea lion wastes seem to fertilize the lush aquatic plant growth, so that rockfish and bottom fish abound in offshore waters. A o Nuevo Island and the adjacent mainland beaches make up one of the most important pinniped rookery and resting areas in central and northern California. Northern elephant seals are the largest, and, in many ways, the most impressive of these animals.
Harbor seals are much smaller and quite wary and elusive.
The tawny brown or yellowish Steller sea lions, which mate on the rocks around the island from mid August, are most often seen on the rocky outer portions of the island. Dark brown California sea lions do not breed at A o Nuevo, but hundreds of them, mostly males, visit the island in September and October, when they use it as a resting place on their annual feeding migration northward from rookeries in Mexico. The characteristic bark of the males is both loud and incessant and can be heard for miles. By contrast, the forlorn, almost human wail of a female who has lost her pup stands out in sharp relief from the cacophony of the males. May. They can often be seen bobbing in the surf just off the reserve's beaches, with only their heads out of the water.