Abalones: Characteristics, Feeding, Reproduction | Sea Life, Islands and Oceania

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ABALONES

Haliotidae (abalones)
ass's-ear abalone (Haliotis asinina)
South African abalone (Haliotis midae)
variously coloured abalone (Haliotis diversicolor)
red abalone (Haliotis rufescens)
green ormer (Haliotis tuberculata)
Abalones are plant-eating marine snails. They are greatly valued by humans. The meat from the foot is considered a delicacy, especially in Asia, and the pearly, iridescent inside of their shells in prized in jewelry making. The meat is marketed fresh, dried, powdered, or frozen in fillets and steaks. The bulk goes to restaurants all over the world. Abalone are also a favorite food of sea otters and the source of nacre, or mother of pearl, a thick iridescent material. They are much less common than they were in the past and some species are in danger of extinction.

Abalones are native to the Pacific. Their shell is ear shaped. The animal crawls around on the bottom of the sea or attaches itself to rocks with the shell facing upwards. It is a grazing animal that feeds on algae and microscopic plants. There are white, red, pink, green and black varieties of abalone. The dispersion of abalone populations tends to depend on food accessibility and habitat structure.

Most abalones are found in cold waters. They attach themselves to rocks with their large muscular foot, which is also edible and highly esteemed. Abalone grow to 30 centimeters (one foot) across. Large abalones, those measuring six inches in length and greater, and found mostly in cool seas in kelp forest. Kelp is their preferred food. They often hang out in crevices and wait for bits of kelp to rain on them.

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Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems

Abalone Characteristics

Abalones are primitive, snail-like, univalve creatures with myopic eyes on the end of retractable stalks, long jet-black tentacles, a large cupped mouth, and a epipodeum (a lateral ridge or fold along either side of the foot bearing appendages and sensory organs). The animals have powerful muscles designed to prevent predators from prying them off rocks. Their blood doesn't have coagulants like mammals so it is easy for them to bleed to death from a minor cut. An abalone's eyes can detect only vague contrasts between light and dark. Its nervous system does not contain a brain. It instead it uses a nerve center with nerve chords leading to ganglia, which control the animal's movements. [Source: NOAA, Candice Middlebrook, Animal Diversity Web (ADW)]

Black abalone anatomy

Abalone have distinctive series of holes in their shells through which water enters the gills, waste products are expelled and sperm and eggs and reproduction are released. The holes fill up and are replaced by new holes as the abalone ages. The abalone's strong, muscular “foot” allows them to hold tightly to rocks and other hard surfaces while The epipodium is an extension of the foot with tentacles used to sense the surrounding environment. [Source: NOAA]

The green abalone reaches lengths of 13 centimeters (5.12 inches). According to Animal Diversity Web: It has a flattened univalve shell scored with wavy lines; five to seven raised holes lie along the shell margin. These holes are used for excurrent water flow in the process of respiration. Its shell length approaches 13 centimeters, and ranges in color from dark shades of maroon to brown.

The inside of the shell is coated with nacre of a lustrous blue-green color. A ruffle of tissue (called the epipodium) lines the edge of the wide, muscular foot which the animal uses to crawl over hard substrata. The foot is cream and brown in color, with tubercles along the edges. [Source: Joshua Williams and Sarah Yesil, Animal Diversity Web (ADW)]

Abalone Shells and the Strong Materials They Are Made From

Abalones are famously known by their desirable iridescent shells. All abalones have natural holes that run along one side, which allow them to draw in seawater for breathing purposes. They vary in size, from an inch to a foot and are roundish, with two to three spirals. The inner spiral is grown into a large "ear"-like shape, which explains their other common name 'ear-shell'. The shell of the Paua abalone ("Haliotis iris") are known for their bright turquoise color. [Source: Heather Hall, AZ Animals, December 27, 2022]

The abalone's shell is an asymmetrical oval in shape, broad and not very convex. It protects them from predators. The iridescent greens, blues, pinks and copper colored layers in the interior of the shell is used as a source of mother-of-pearl for art, and it is also found in many common decorative items such as buttons, ornaments, and trinkets

abalone shell

Abalones makes their shell out of calcium carbonate, the same material of which chalk is made. The innermost layer of abalones are made of a type of calcium carbonate called nacre, or mother-of-pearl, which in the past was widely used for jewelry and other decorative arts. Colors vary from different species but the inside of abalone shells are often beautifully shiny, from silvery white to turquoise, green, blue and red mother-of-pearl. [Source: Nicholas Argent, Citrus Reef]

The shells of abalones are also known for being exceptionally strong. They are as tough as Kevlar and 3000 times harder than chalk. Their strength is derived from the way the material is organized the into staggered, nanoscale bricks through a subtle play of 15 different proteins. Several teams of scientists are studying the structure and hoping to replicate it but still they admit they don’t even really understand the most basic things about it. Materials modeled on abalone nacre, or mother or pearl, are as strong as steel at half the weight and perform very well in bullet stopping tests: a tungsten rod forced at 2,000mph made it only halfway through the abalone-like material.

Abalone Behavior

Abalone are slow-moving bottom dwellers. They attach to rocks and other hard surfaces using their muscular foot and, when disturbed, they become difficult or impossible to remove. An abalone can also use its foot to move across surfaces. Metabolic rates are influenced by temperatures. Grazing and reproduction occupy most of the life of an abalone. [Source: NOAA]

Abalone live sedentary lives, remaining in the same general area all its life. They move around by shuffling forward their massive muscular foot, which has a surface area usually equal to the shell diameter. There is a very powerful huge suction cup with considerable surface adhesion. Because of this foot, the abalone has a remarkable way of protecting itself and becoming nearly invulnerable to its predators, which are mainly rock crabs, octopus, bottom-feeding fish, and the sea otter. Using its foot, it can both propel forward at a considerable speed, and cling firmly to a rock. [Source: By Candice Middlebrook, Animal Diversity Web (ADW)]

pinto abalone shell and animal

Green abalone are nocturnal, solitary creatures that lives under rocks and in crevices in shallow areas. They only move around if algae is scarce. Otherwise they are sedentary, sessile (fixed in one place) creatures. Depending on food availability, abalone may stay in the same general area for months. Abalone are known to compete with sea urchins for crevices in rocky substrates, but they do not formally defend a territory. [Source: Joshua Williams and Sarah Yesil, Animal Diversity Web (ADW)]

According to Animal Diversity WebGreen abalone uses its ruffled epipodium and tentacles along the inside of the foot to sense its environment. Green abalones have a pair of eyes that detect light and shadow. Individuals have olfactory senses to detect chemicals released by conspecifics that induce spawning. The sperm and eggs of green abalone communicate (in a way) through chemicals. Dissolved signal molecules cause sperm to accelerate towards an egg. Through the use of nuclear magnetic resonance spectroscopy, the sperm attractant was found to be the amino acid L-trytophan.

Abalone Feeding

Abalone are strict vegetarians that feeding primarily on kelp, plankton and sessile (fixed in one place) macro-algae. Adults eat different types of algae than larvae. They can catch kelp drifting along the seabed or eat kelp still attached to rocks. Like all gastropods, abalone use their toothed radula to scrape and ingest their food.

According to Animal Diversity Web (ADW): In the southern part of its geographical ranges, they consume mainly giant kelp, and in the northern ranges, bull kelp. Abalones are able to detect food only at close proximities. Once food is detected, the abalone carefully glides slowly along, feeling its way, until it reaches the alga. It then raises its foot and comes down on the plant, trapping it beneath its body. It then consumes the alga, using its small rasplike teeth and extruding tongue, which often measures one-third of the animal's total body length. If interfered with while feeding, the abalone instantly clamps down, pulling its shell over its soft body. In this position it is difficult for most predators to remove the abalone from its substrate. [Source: By Candice Middlebrook, Animal Diversity Web (ADW)]

The diet of the green abalone mainly consists of drift and attached seaweed. Species composition of the diet is directly related to the species abundance of algae in the environment. The green abalone prefers fleshy red algae, and when food is scarce, it is forced to forage.

Abalone Predators and Ecosystem Roles

The abalone is prey to any creature that can dislodge it from its rock. Predators include seals, sea lions, sea otters, fish, octopus sea stars and humans. The abalone's greatest natural predator is the sunflower star (Pycnopodia helianthoides). The sunflower star has no problem with the shell as it simply engulfs the entire abalone and digests it. The only anti-predator defense that abalone have against it is by clamping down onto its rock or by crawling away from its predator. [Source: Joshua Williams and Sarah Yesil, Animal Diversity Web (ADW)]

According to Animal Diversity Web; Abalone have a large role in the coastal ecosystem; as a herbivorous grazer it affects algal recruitment onto bare surfaces via its radular scraping while feeding. As a juvenile, the green abalone is easy prey for secondary consumers. The young seek refuge among rocks and under the spine canopy of the red sea urchin Strongylocentrotus franciscanus. The sea urchins protect the abalone from predators in a commensal relationship. In many cases, areas with low counts of sea urchins also show low counts of abalone. However, as the abalone grow and reach adult size, they no longer need protection from sea urchins, and competition for space begins, as both creatures prefer to inhabit the same microhabitat of rock crevices.

The abalone's shell provides a hard surface substrate for bottom-dwelling organisms to colonize, including various benthic invertebrates such as worm snails, sponges, date mussels, and bryozoans. As a result of their sedentary lifestyle, abalones can easily become covered with marine growths and serve as refuges for other small creatures. The large, flat shell may support a modest community of algae, sponges, barnacles, bryozoan, and hydroids. As many as 90 species of small living gastropods have been found living on the shells.

Abalone Reproduction, Development and Lifespan

Abalone are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). Both males and females reach sexual maturity at ages two to five years. Abalone breed frequently throughout the year. Some species lay more than 10 million eggs at a time when they spawn. Some are very fussy and breed only in the right conditions. A big problem among some species is that males and females are so dispersed that when the females release their eggs there is sperm around to fertilize them.

Abalone are “broadcast spawners,” releasing eggs and sperm into the water by the millions when environmental conditions are right. They release sperm or egg into the water column if they sense others have done so.The eggs hatch after only one day if fertilized, but large amounts of sperm are needed to fertilize an egg. This means fertilization succeeds more often when groups of adult male and female abalone are close to each other when they spawn. Fertilized eggs hatch into larvae, which settle and grow into adults. [Source: NOAA]

black abalone life cycle

During broadcast spawning, abalones release thousands of sperm and eggs into the water column; thus, fertilization is external. The number of offspring ranges between 10,000 to 11 million with the average number being around 5.5 million. The gestation period ranges from 20 to 30 hours There is no parental investment after eggs and sperm are released as they are a broadcast spawner. [Source: Joshua Williams and Sarah Yesil, Animal Diversity Web (ADW)]

According to Animal Diversity Web: Abalone passes through several life stages. First the egg is fertilized, and hatches after 20 to 30 days. The egg hatches into a trochophore larva, a free-swimming, ciliated planktonic stage. This develops into the next stage, a free-swimming veliger larva. The veliger eventually sinks to the ocean floor, and becomes a sedentary juvenile. Eventually, juveniles develop into reproductive adults.

Lifespan in the wild is estimated at 30 or more years. Mortality rate of young abalone is high because of predation. Lifespan is also limited by the amount of available food. Since the abalone’s diet mainly consists of drifting algae, its lifespan is directly related to the persistence of kelp forests. Due to destruction of the kelp beds via human activities and natural events, lifespan of abalone can be affected greatly.

Threatened Abalone

Abalone was once plentiful but now is regarded as an endangered species in many place. Their numbers have been depleted by overfishing. In the early 20th century and up until the 1970s, abalone supported huge commercial and sport fisheries. Due to overfishing and disease, today's abalone faces extinction — both white abalone and black abalone are listed as endangered under the Endangered Species Act.

abalone and asparagas and black bean sauce

About 2,800 metric tons of red abalone from approximately 80, 000 individuals are taken in annually in 1990s. In the recent past, the abalone has been over-fished and exploited by fisheries, and by commercial and sport divers. As a result, abalone populations have been drastically reduced. California has passed many strict regulations in order to keep the abalone population flourishing. These laws include protecting abalone smaller than 8 inches in diameter, prohibiting the canning of abalone, and also prohibiting the shipment of fresh or frozen meat out of state. An Abalone Recovery Management Plan has been implemented through the state of California. NOAA is also active in abalone recovery.

Reduced numbers make the species vulnerable to local extinction due to a phenomenon known as the Allee effect. The Allee effect describes a situation whereby a decrease in population size leads to decreases in reproduction and survival of individuals. In the case of green abalone, this effect is likely due to increased distance between males and females as the population density decreases, leading to reproductive failure.

Abalone are also threatened by disease. Withering syndrome, one common type of infection, is a fatal disease that affects the digestive organs of abalone. The pathogen that causes it is currently present in the coastal oceans of southern California. Even abalone that don't have the disease can carry the pathogen that causes it. Die-offs from disease are associated with sea surface warming events (such as, El Niño events, thermal discharges).

Other abalone diseases have emerged over the past several decades in abalone populations outside of California (such as, herpes virus, vibriosis, sabellidosis). To date, no outbreaks of these diseases have been observed in U.S. abalone populations. Strict regulations and monitoring are needed whenever animals are imported and/or transported between facilities, to minimize the potential for introducing these diseases to wild abalone populations. [Source: NOAA]

Abalone Divers Attacked by Great White Sharks

Japanese abalone diver circa 1900

In August 2004, 50-year-old Randy Fry was decapitated while diving for abalone on theMendociono coast just north of Fort Bragg. California. Cliff Zimmerman was only three feet away from Fry, his old friend and diving partner, when he heard a noise and felt the pressure of something big moving by. “It was a shark, and it came out of nowhere, it came fast, and it killed him, Zimmerman said. Fry’s wet suit was found a day later. [Source: Carl Nolte, San Francisco Chronicle, August 17, 2004]

In January 2007, an abalone diver survived being partly swallowed head first by a great white shark off cape Howe, about 400 kilometers south of Sydney, Australia. The diver, 41-year-old Eric Nerhus, was grabbed by a shark estimated to be about three meters long. It swallowed his head and his face mask, breaking his nose, then let go and came back for second bite.

A fellow diver who witnessed the attack said, “The brunt of the attack was taken by lead weight-vest. It’s all over your torso. The bite left deep lacerations on his side but Nerhus managed to wrestle free and poke the shark in the eye. A rescuer who who helped bring Nerhus to the hospital told reporters, “When he came to us he was conscious and alert but had a broken nose and lacerations to both sides of torso and chest — bite marks all the way around.” Nerhus’s 25-year-old son help pull him from the water.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated May 2023