Several species of molluscs related to the limpets. Also known as ormer, sea ear, or earshell, the abalone (four syllables, the final e being sounded) somewhat resembles a snail, the body being little more than a muscular foot with a head at one end, bearing a pair of eyes and sensory tentacles. The body is also fringed with tentacles.
Along the side of the shell is a line of holes, through which water is exhaled after it has been drawn in under the shell and over the gills to extract oxygen. New holes are formed as the shell grows forward, while the old holes become covered over, so that only a few younger holes are open at any one time, the rest appearing as a line of bumps.
Some abalones are among the largest shellfish: they range in size from the 1 in. long and very rare Haliotis pourtalese to the red abalone of California, which is up to 10 in. across
Distribution, habitat and habits
Abalones are to be found in many parts of the world: along the coasts of the Mediterranean, Africa, Australia, New Zealand, the Pacific islands, and the western coast of North America. In the Atantic they are found as far north as St. Malo and the Channel Islands. The rare species Haliotis pourtalese is found off Florida. It is known mainly from specimens washed up on the shore, as it lives at depths of 350—1,200 ft. It is thus the deepest-living of all abalones the rest live between the extreme low-water mark and a depth of about 60 ft along rocky shores where there is no sand to clog the gills or in rocky pools large enough not to be heated too quickly by the sun. The only other exception is the black abalone, which lives in the splash zone where waves breaking against rocks alternately and expose it
Unlike their limpet relatives, abalones have no “home”, no spot on a rock where they return after feeding. They simply hide up in a crevice or under a rock, avoiding the light and coming out at night. When disturbed an abalone grips the rock face, using its foot as a suction pad: the two main muscles of the body exert a tremendous force—up to 400 Ib in a 4 in specimen Unlike the limpet, the abalone cannot bring its shell down over the whole of its body: the edge of the foot, with its frill of tentacles, is left sticking out.
Abalones move in the same way as limpets and snails. Waves of muscular contraction pass along the foot, pushing it forward. As each part expands it is fixed to the ground by slimy mucus: the part in front, expanding in turn, is pressed forward and then itself stuck down. Abalones differ from limpets and snails in having a sort of bipedal movement pass down either side of the foot, so that as part of one side is moving the corresponding part of the other side stays fixed. The rate of travel is vert rapid for a shellfish: a speed of 5-6 yd/min has been recorded – although no abalone would cover this distance in one dash.
Many-toothed tongue for feeding
Abalones are vegetarians, crawling over rock faces and browsing on seaweeds that they seek out with their sensitive tentacles. Their favourite foods are the delicate red weeds and green sea lettuces, although they also scrape tissue off fragments of kelp that have been torn away by waves. Young abalones eat the forms of life that encrust rocks, such as the coral-like plant Corallina.
Food is scraped up and chewed into small pieces by the rasp-like action of the radula, a tongue made up of large numbers of small, chalky teeth
100,000 eggs laid
Some molluscs are hermaphrodite but all individual abalones are of one sex or other. They reach sexual maturity at 6 years. The germ cells, or gametes, are shed directly into the sea, causing great wastage. Thus a female will liberate 100,000 or more eggs, and the sea around a male turns milky over a radius of 3 ft when he sheds his milt. To reduce wastage, however, female does not shed eggs until induced by the presence of sperms around her.
The fertilised eggs are covered by a gelatinous coat and float freely in the sea until they few hours later as minute trochophore larvae. These trochophore larvae are top-shaped and swim around by means of a band of hair-like cilia around the thickest part. Within a day the trochophore develops into a veliger — a miniature version of the adult complete with shell but still with the band of cilia, sinks to the bottom and starts to develop into an adult, a process that takes several weeks.
The free-swimming larvae have advantages in that they are the means by which the otherwise rather sedentary abalones can spread, but they are very vulnerable and are
eaten in their millions by plankton-eating fish like anchovies and herrings.
Although mortality is heaviest during the free-swimming stage, adult abalones also have several enemies. Fish, sea birds, sea otters, crabs and _ starfish dislodge the abalones or chew bits off them. Their only protection lies in their tenacity in clinging to rocks and the protective camouflage of the shell and foot. This camouflage is improved by the seaweeds and sedentary animals that settle on the shell. Also, it has been found that when young abalones feed on red weeds their shells become red.
On the other hand abalones are more vulnerable due to the boring sponge Cliona lobata, which erodes holes in their shells and so opens them up to other predators. In the Channel Islands as many as 95% of a sample of abalones have been found to be infected with boring sponges.
Dark pearls, called blister pearls, are sometimes found in abalones. Like the real pearls of oysters, these are formed by the animal to cover up a source of irritation — in this case a minute parasitic clam, Pholadidea parva, that bores through the abalone’s shell and into its tissues.
Prized for shell and meat
The shells of abalones are prized because, although they are superficially rough and dull, cleaning reveals the gleam of mother of pearl. This and the large size of the shell make abalones popular with shell collectors, and they are also used for making costume jewellery. The body itself is much esteemed as food. The large foot is cut into strips, beaten with a mallet to make it soft, and then fried. The edge of the foot is trimmed off to make chowder.
The popularity of abalones and the ease with which they can be collected from the shore has led to stocks being severely depleted. In California, which is the centre of the abalone industry, only strict laws have prevented its extinction. As abalones do not breed until they are six years old and perhaps 4 in. long, there is a minimum length at which they can be taken: for the common red abalone this is 7 in., corresponding to about 12 years of age. There is a close season though it abalones breed all the year round — and catches are limited to five a day and can only be taken by a licence-holder
Finally, abalone meat cannot be exported from the State of California. This does not mean, however, that it cannot be obtained outside California, as tinned abalone meat is exported from Mexico and Japan, and today most of the abalone eaten in the United States are imported from Mexico. The abalone breathes through the line of holes along its shell. As it grows, new ones form and others are covered over.