Red Abalone Shell, Haliotis rufescens

Red Abalone Shell, Haliotis rufescens. Shell collected from coastal waters off San Diego, California, June 2009. Size: 26 cm (10.2 inches) x 21 cm (8.3 inches). Collection, photograph and identification courtesy of Bob Hillis, Ivins, Utah.

Phylogeny: The Red Abalone Shell, Haliotis rufescens (Swainson, 1822), is a gastropod mollusk that is a member of the Haliotidae Family of Abalone Shells. The genus Haliotis is the only genus in this family, and there are sixty-nine species in this genus. They are known in Mexico as Abulón Colorado.

Description: Red Abalone are the largest abalone species in the world. The shell has an oval profile and is somewhat flattened. There are four open holes or three holes and a notch along the margin. The shell is sculpted by fine spiral ridges and radiating waves. The exterior of the shell is a dull brick-red in color that usually extends onto the lip of the shell, opposite the line of holes. The interior of the shell is an iridescent mix of blue, green, silver, pink, and brown with pink being the dominant color. The epipodium is black with white fringe and black tentacles. Red Abalone Shells reach a maximum of 31.3 cm (12.3 inches) in length and 25.3 cm (10.0 inches) in height. Red Abalone readily hybridize with other abalone species, making an identification difficult.

Habitat and Distribution: Red Abalone are found on rocks and in crevasses from just below the low water mark to depths up to 165 m (540 feet). They are a temperate to subtropical Eastern Pacific species that have a limited distribution in Mexican waters of the Pacific Ocean being found north of Bahía Tortugas, Baja California Sur, along the central and northwest coasts of the Baja Peninsula.

Ecology and Behavior: Red Abalone are nocturnal herbivorous grazers that feed primarily on red and brown algae. They’ll eat attached or drift algae. Their predators include, fish, marine mammals, octopuses and sea stars. They are gonochoric and reproduce sexually, through broadcast spawning, with external fertilization. Spawning takes place between mid-February and mid- April. They are sexually mature at around four years, and can live for more than  twenty years. They are known to host multiple species of epibionts, including algae, barnacles, bryozoans, hydroids and sponges. As many as 90 species of small living gastropods have been found living on the shells. Some of these epibionts are ectoparasites such as the Odostome Snail, Evalea tenuisculpta. They also host ciliates, endoparasitic coccidians, haplosporidians, nematodes and protists, which can cause a disease called “abalone wasting disease”. From a conservation perspective the Red Abalone is current considered to be Critically Endangered. Red Abalone were used by indigenous cultures as a food source, and the shells used as tools and jewelry. They have historically been the target of commercial and recreational fisheries. Severe overfishing and the abalone wasting disease have caused Red Abalone populations to plummet and recovery efforts have been slow and unpredictable.

Synonyms: Haliotis californiana, Haliotis hattorii, Haliotis ponderosa, and Haliotis rufescens hattorii.