Mollusc - Abalone

Abalone,
common name for any marine snail or Gastropod in the Mollusc phylum, genus Haliotidae.

KINGDOM:
Animalia

PHYLUM:
Mollusca

CLASS:
Gastropoda

SUB-CLASS:
Prosobranchia

SUB-ORDER:
Archaeogastropoda

GENUS:
Haliotidae


Red Abalone
Haliotis rufescens
Abalone are primitive, single shelled molluscs that attach themselves to rocks along the open ocean coastline where the water is less than 35 m deep. They are found in all warm seas except for the western Atlantic Ocean. They do not occur where there is freshwater outflow and are not usually found out in the open on barren rocky reefs. The preferred environment for abalone are crevices, caves, under ledges and the gaps between large boulders.

Because they live in the swell zone, abalone have evolved a strong muscular foot with which they hang onto the substrate. This foot is sought as a delicacy.

There are about 100 species of abalone in the world and around 13 of these are found around the Australian coastline. The blacklip abalone, Haliotis ruber, is found along the coast of New South Wales.

Abalone feed on seaweed. They have flattened, ovoid shells that are asymmetrical, sometimes 30 cm long. The shape resembles the human ear, hence another common name, ear shell, or sea ear. The abalone’s shell is streamlined for minimal resistance to the movements of its intertidal, or shallow-water habitats.

Holes along the side of the abalone’s shell occur naturally and allow waste and the water currents from which the animal obtains oxygen to exchange freely. As the abalone grows, these holes fill up and new ones appear.

Growth is extremely variable but, generally, blacklip abalone are 3 years old when they reach maturity (about 95 mm) and 4-5 years old when they reach the legal minimum length for harvesting of 115 mm.

Abalone have separate sexes that do not change, unlike other species such as the oyster. The gonad (sex gland) is a cone-shaped appendage to the gut. It is white or cream in males but varies from green to grey or brown in females.

Spawning occurs over summer to autumn, and varies from place to place and between years, probably depending on the water temperature. the male spawns first by pumping sperm into the surrounding water through the shell pores. The female responds by doing the same with her eggs.

Fertilization occurs in the water. After 3 to 6 days a shell forms and the abalone settles on a suitable substrate.

there is some evidence that the settling juveniles are attracted to the slime trails of adults, or that in some other way they are guided to settle only on surfaces where adult abalone e nearby.

Once they settle, juveniles make random movements around their environment looking for food and a suitable homesite. They will select homesites where drift algae are carried to them by water movement, and after they reach about 2 years of age, may never move again. If they do move , it will not be far. The maximum recorded movements for abalone are about 200 m.


Abalone shell
The shells are used by humans in the manufacture of decorative objects, such as, buttons and jewelry. (Mother-of-Pearl).

Mother-of-Pearl, is the hard, iridescent inner layer of certain shells, such as that of the abalone, pearl oyster, and mussel. Also called nacre, it is composed chiefly of calcium carbonate deposited in thin, overlapping layers, together with some organic matter. The iridescent play of colors is caused by the interference of reflected light waves.

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