Abalone
Abalone, in singular "an abalone", are sea snails in the genus Haliotis, the only genus in the family Haliotidae. Abalone shells are distinctive for their flattened, ear-like shape, nacreous interior, and row of holes used for respiration. The flesh of abalone is widely considered to be a delicacy, and is consumed raw or cooked by a variety of cuisines. Abalone are globally distributed, with approximately 70 known species alive today. Though some species are small, the largest abalone can attain a length of.
Names
Other common names for abalone are ear shells, sea ears, and, now rarely, muttonfish or muttonshells in parts of Australia, ormer in the United Kingdom, perlemoen in South Africa, and pāua in New Zealand.Description
Most abalone vary in size from to. The largest species, Haliotis rufescens, reaches.The shells of abalone have a low, open spiral structure, and are characterized by several open respiratory pores in a row near the shell's outer edge. The thick inner layer of the shell is composed of nacre, which in many species is highly iridescent, giving rise to a range of strong, changeable colors which make the shells attractive to humans as ornaments, jewelry, and as a source of colorful mother-of-pearl.
The shell of abalone is convex, rounded to oval in shape, and may be highly arched or very flattened. The shell of the majority of species has a small, flat spire and two to three whorls. The last whorl, known as the body whorl, is auriform, meaning that the shell resembles an ear, giving rise to the common name "ear shell". Haliotis asinina has a somewhat different shape, as it is more elongated and distended. The shell of Haliotis cracherodii cracherodii is also unusual as it has an ovate form, is imperforate, shows an exserted spire, and has prickly ribs.
A mantle cleft in the shell impresses a groove in the shell, in which are the row of holes characteristic of the genus. These holes are respiratory apertures for venting water from the gills and for releasing sperm and eggs into the water column. They make up what is known as the selenizone, which forms as the shell grows. This series of eight to 38 holes is near the anterior margin. Only a small number is generally open. The older holes are gradually sealed up as the shell grows and new holes form. Each species has a typical number of open holes, between four and 10, in the selenizone. An abalone has no operculum. The aperture of the shell is very wide and nacreous.
The exterior of the shell is striated and dull. The color of the shell is very variable from species to species, which may reflect the animal's diet. The iridescent nacre that lines the inside of the shell varies in color from silvery white, to pink, red and green-red to deep blue, green to purple.
The animal has fimbriated head lobes and side lobes that are fimbriated and cirrated. The radula has small median teeth, and the lateral teeth are single and beam-like. They have about 70 uncini, with denticulated hooks, the first four very large. The rounded foot is very large in comparison to most molluscs. The soft body is coiled around the columellar muscle, and its insertion, instead of being on the columella, is on the middle of the inner wall of the shell. The gills are symmetrical and both well developed.
These snails cling solidly with their broad, muscular foot to rocky surfaces at sublittoral depths, although some species such as Haliotis cracherodii used to be common in the intertidal zone. Abalone reach maturity at a relatively small size. Their fecundity is high and increases with their size, laying from 10,000 to 11 million eggs at a time. The spermatozoa are filiform and pointed at one end, and the anterior end is a rounded head.
The larvae are lecithotrophic. The adults are herbivorous and feed with their rhipidoglossan radula on macroalgae, preferring red or brown algae. Sizes vary from to, while Haliotis rufescens is the largest of the genus at.
Distribution
The haliotid family has a worldwide distribution, along the coastal waters of every continent, except the Pacific coast of South America, the Atlantic coast of North America, the Arctic, and Antarctica. The majority of abalone species are found in cold waters, such as off the coasts of New Zealand, South Africa, Australia, Western North America, and Japan.Evolutionary history
Abalone are members of the clade Vetigastropoda, though their precise position within the clade is uncertain. Despite their inclusion in the order Lepetellida, they do not appear to be particularly closely related to other members of the order and may be more closely related to Trochoidea, or alternatively outside of a clade uniting Trochoidea with the rest of Lepetellida. The earliest known fossil abalone are known from the Campanian age of the Late Cretaceous. The few known Cretaceous abalone fossils have all been found in North America, suggesting that the group may have originated there, although other possibilities have been suggested, including a central Indo-Pacific origin based on where abalone are most diverse today. Haliotidae may have evolved from the pleurotomariidan families Temnotropidae or Trochotomidae. Trochotoma frydai, from the Campanian of Spain, closely resembles the Cretaceous abalone Haliotis antillesensis except in having a slit instead of a row of tremata.Structure and properties of the shell
The shell of the abalone is exceptionally strong and is composed of a tightly packed calcium carbonate matrix. Layered among the matrix is an endogenous protein further strengthening the shell. Due to the unique structure of the shell, a force applied directly to the shell matrix will more likely cause the shedding of layers as opposed to cracking or shattering. Material scientists are currently studying this structure for insight into stronger ablative protective tools such as body armor.The dust created by grinding and cutting abalone shell is dangerous; appropriate safeguards must be taken to protect people from inhaling these particles.
Diseases and pests
Abalone are subject to various infectious diseases. The Victorian Department of Primary Industries said in 2007 that ganglioneuritis killed up to 90% of stock in affected regions. Abalone possess very little clotting factor, meaning even a mild to moderate skin-piercing injury can result in death from fluid loss. Members of the Spionidae of the polychaetes are known as pests of abalone.Human use
Abalone have been harvested as a seafood and esthetics since prehistory. Abalone shells and associated materials, like their claw-like pearls and nacre, have been used as jewelry and for buttons, buckles and inlay. These shells have been found in archaeological sites around the world, ranging from 100,000-year-old deposits at Blombos Cave in South Africa to historic Chinese abalone middens on California's Northern Channel Islands. For at least 12,000 years, abalone were harvested to such an extent around the Channel Islands that shells in the area decreased in size four thousand years ago.Farming
of abalone as a meat product began in the late 1950s and early 1960s in Japan and China. Since the mid-1990s, there have been many increasingly successful endeavors to commercially farm abalone for the purpose of consumption. Overfishing and poaching have reduced wild populations to such an extent that farmed abalone now supplies most of the abalone meat consumed. The principal abalone farming regions are Mainland China, Taiwan, Japan and South Korea. Abalone is also farmed in Australia, Canada, Chile, France, Iceland, Ireland, Mexico, Namibia, New Zealand, South Africa, Spain, Thailand and the United States.After trials in 2012, a commercial "sea ranch" was set up in Flinders Bay, Western Australia to raise abalone. The ranch is based on an artificial reef made up of 5,000 separate concrete abalone habitat units, which can host 400 abalone each. The reef is seeded with young abalone from an onshore hatchery.
The abalone feed on seaweed that grows naturally on the habitats; the ecosystem enrichment of the bay also results in growing numbers of dhufish, pink snapper, wrasse, and Samson fish among other species.
Consumption
Abalone have long been a valuable food source for humans in every area of the world where a species is abundant. The meat of this mollusc is considered a delicacy in certain parts of Latin America, France, New Zealand, East Asia and Southeast Asia.In the Greater China region and among overseas Chinese communities, abalone is commonly known as bao yu, and sometimes forms part of a Chinese banquet as one of the four sea delicacies of Chinese cuisine. In the same way as shark fin soup or bird's nest soup, abalone is considered a luxury item, and is traditionally reserved for celebrations.
In Japan, live and raw abalone are used in sushi or served steamed, salted, boiled, chopped, or simmered in soy sauce. Salted, fermented abalone entrails are the main component of tottsuru, a local dish from Honshū. Tottsuru is mainly enjoyed with sake.
In South Korea, abalone is called Jeonbok and used in various recipes. Jeonbok porridge and pan-fried abalone steak with butter are popular but also commonly used in soups or ramyeon.
In California, US, abalone meat can be found on pizza, sautéed with caramelized mango, or in steak form dusted with cracker meal and flour. As abalone became more popular and less common, the prices adjusted accordingly. In the 1920s, a restaurant-served portion of abalone, about, would cost about US$7; by 2004, the price had risen to US$75. In the United States, prior to this time, abalone was predominantly eaten, gathered, and prepared by Chinese immigrants. Before that, abalone were collected to be eaten, and used for other purposes by Native American tribes. By 1900, laws were passed in California to outlaw the taking of abalone above the intertidal zone. This forced the Chinese out of the market and the Japanese perfected diving, with or without gear, to enter the market. Abalone started to become popular in the US after the Panama–Pacific International Exposition in 1915, which exhibited 365 varieties of fish with cooking demonstrations, and a 1,300-seat dining hall.