Red Abalone

The red abalone’s shell exterior is brick red to pink, with 3-4 oval, open respiratory pores that are externally raised above the shell surface. Abalone “breathe” through these pores, under which their gill chambers are located. Algae growth often obscures their coloration. Their shell interior is iridescent with a large, oval muscle scar. Their mantle and tentacles are black, and the underside of the foot is slightly yellow. The shape of the shell depends on its habitat – if they grow into an adult in a rocky crevice where there are strong currents, the shell forms into a flat, low profile. If the abalone grows into an adult in an open area with little current, its shell will be highly rounded.

Abalone are slow-growing, and most California abalones mature between 3-7 years and can live up to 35-54 years. Wild red abalone can grow up to 10 in (26 cm). They are the largest in the Haliotis genus. Farmed abalone average about 4 in in length (10 cm) and can take 3-4 years to reach marketable size. When abalone grows, the mantle edge adds new material to the shell’s outer rim, increasing the shell diameter and adding new layers to the inside, which thickens the shell.

Red abalone are herbivores and feed on algae like drift kelp. During El Niño events when ocean temperatures are higher, kelp abundance decreases, which slows down shell growth, especially in Southern California. Their main predators are sea otters and humans.

They are broadcast spawners and spawn in the spring and early summer. Fecundity is directly related to adult size, so older and larger individuals are significantly more productive. A large adult can spawn as many as 6 million eggs, while a young female can only broadcast a few thousand. Because abalone are broadcast spawners, successful fertilization is also heavily reliant on other large adult populations living in close proximity. A minimum density of spawners no more than 5 ft (1.5 m) apart is essential for successful fertilization. The spawning season in Northern California occurs from April to July, which reflects the seasonal availability of kelp.  In Southern California, spawning can occur year-round. When one abalone begins to spawn, it triggers the spawning of others in the aggregation. Embryos develop into planktonic larvae and juveniles develop two ciliated flaps for swimming and feeding, eventually maturing into fully grown adults.