Haliotis rufescens (red abalone) is a species of very large edible sea snail in the family Haliotidae, the abalone, ormers (British) or pāua. It is distributed from British Columbia, Canada, to Baja California, Mexico. It is most common in the southern half of its range. Red abalone is the largest and most common abalone found in the northern part of the state of California, United States.
Habitat Red abalone live in rocky areas with kelp. They feed on the kelp species that grow in their home range, including giant kelp (Macrocystis pyrifera), feather boa kelp (Egregia menziesii), and bull kelp (Nereocystis luetkeana). Juveniles eat coralline algae, bacteria, and diatoms. They are found from the intertidal zone to water more than 180 m (590 ft) deep, but are most common between 6 and 40 m (20 and 131 ft).
Shell description The red abalone's shell length can reach a maximum of 31 cm (12 in), making it the largest species of abalone in the world. The shell is large, thick, dome-shaped, and usually covered with barnacles, vegetation, or other marine growth making the color and shell sculpture difficult to determine. It is usually a dull brick red color externally. Typically the shell has three to four slightly raised oval holes or respiratory pores, although specimens with no holes and others with more than four have been found. These holes collectively make up what is known as the selenizone which form as the shell grows. The inside of the shell appears polished and is strongly iridescent. A central, prominent muscle scar is easily visible in the shells of most Red Abalone, marking the location at which Haliotis rufescen's strong columellar muscle attaches. This species was used as the subject in a study of the microscopic development of nacre.
Tentacles, foot and epipdodium Below the edge of the shell, the black epipodium and tentacles can be seen. The underside of the foot is yellowish white in color.
Sex ratio Female members of dioecious molluscan species have been known to be more common than males. In populations that experience human predation, this difference can be exacerbated, as is the case with populations of Haliotis rufescens. From 1972-1973, researchers studying red abalone populations at Point Cabrillo Lighthouse Station and Van Damme State Park found that the level at which human predation occurs can have profound effects on the age class structure of each population. For many years, the abalone at Van Damme were heavily fished and the population structure reflected a notable lack of larger, older individuals. At Point Cabrillo, abalone harvesting had halted for some time, and populations of red abalone showed the development of a natural age class structure and sex ratio.
Diseases Red abalone are subject to a chronic, progressive and lethal disease: the withering syndrome or abalone wasting disease caused by Rickettsiales-like prokaryotes. This disease has had a historically grim effect on the species overall, decimating populations across their native habitat. Today, the effects of withering syndrome on current populations are poorly understood, but populations are still low. Elevated water temperatures have been shown to speed up the progression and transmission of withering syndrome in infected individuals. Exposed abalone experiencing starvation at 18.0 °C are far more likely to become infected than exposed individuals at 12.3 °C. This was shown in a 2005 study which was the first to indicate that temperature has a significant effect on Rickettsiales-like, prokaryote induced wasting syndrome transmission.
History of human use Red abalone has been used since prehistoric times—red abalone shells have been found in Channel Island archaeological sites dated to nearly 12,000 years old. Red abalone middens—refuse deposits where red abalone shells are a major constituent—are abundant in archaeological sites of the Northern Channel Islands dated between about 7500 and 3500 years ago. The Native American Chumash peoples also harvested this species along the Central California coast in the pre-contact era. The Chumash and other California Indians also used red abalone shells to make a variety of fishhooks, beads, ornaments, and other artifacts.
History of diseases
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