Abalone, or perlemoen as we call it here in South Africa, is the name for a group of large, flat sea snails of the genus Haliotis. That may not sound remarkable, but abalone has come to champion the cause for marine conservation by showing the world the dangers of overfishing.
Want to see and learn about abalone? Be sure to check out the perlemoen in a simulated rock pool in the Skretting Diversity Gallery on your next Two Oceans Aquarium Visit.
Often underappreciated, perlemoen truly have their own hidden beauty. Image courtesy National Geographic/Craig Foster
When South Africans refer to "perlemoen", we are usually thinking of the Midas ear abalone (Haliotis midae) - but there is a whole lot more to abalone than this one species.
Perlemoen isn't the only endangered South African treasure at the Aquarium - here are 16 more that you can see here.
These slow-growing animals are at severe risk of further decline in South African waters. They are threatened by poaching, poor fishery management and invasion by non-endemic species. By understanding abalone, we can play a role in securing its future.
What is abalone?
Abalone is a mollusc and part of a family that includes clams, mussels, sea slugs and octopuses. More specifically, it is a gastropod - literally meaning "stomache on a foot". It is a flattened sea snail with ear-shaped shells, which inhabits coastal waters across the world. The spiral seen in most sea snails is not easily seen in abalone, as it remains flat and open. The abalone shell is thickened with layers of nacre (mother-of-pearl) - iridescent layers of plates of a mineral called aragonite.
Image courtesy @Biz_CSI
Its soft body is surrounded by a shell-secreting mantle, a head and a very large muscular foot. The outer edge of the foot is called an epipodium, a sensory organ that is covered by a host of tentacles. The arrangement of tentacles, colours and patterns on this epipodium is unique to each species of abalone.
Image courtesy National Geographic/Craig Foster
The shell is attached to the abalone's body by a strong shell muscle (which gives the abalone some cool abilities, which we'll have a look at later). The shell has a set of characteristic holes, which the perlemoen uses to vent water through its gills. The gill chamber, a part of the body near these holes, is used to eject all of the abalone's waste into the water.
Between the foot and shell, the abalone's organs are arranged in a circular pattern. Its largest organ is its gonad, the reproductive organ found on the opposite side of the abalone from its shell pores. The gonad is pale in colour in males and dark grey-green in females - but only takes on its colour in sexually mature abalone.
Image courtesy Marine Science.
On its head, an abalone has a pair of eyes and large tentacles, which it uses to find algae to feed on. Inside its mouth is a large, rough tongue which it uses to file food off of rocks and to break up kelp. Abalone does not have a centralised brain, but the network of nerves throughout its body serves the same function.
All abalone, including this northern abalone, use their barbed tongues or "radula" to scrape apart algae for consumption. Image courtesy Seattle Aquarium.
What makes abalone awesome?
Contrary to what you might think, this snail isn't a slowpoke - it uses its one powerful foot to outrun would-be predators.
Using its strong foot muscles, an abalone can rapidly flip predators off of its shell.
Here's another angle. These aren't defenceless snails at all!
Abalone is weird! That's why it's on our list of weirdest ocean animals of all time.
The 5 South African abalone species
Courtesy of Gastropods.com
Perlemoen (Haliotis midae)
H midae is the largest of the five species found here, and the one most people think of when they hear "perlemoen". It is very large and can grow up to 23cm across.
Its shell is corrugated at irregular intervals, with "furry" projections of simple tentacles protruding from the shell's edge. It inhabits shallow reefs, feeding on kelp and red algae along the coasts of the Western and Eastern Capes.
Courtesy of Gastropods.com
Spiral-ridged siffie (Haliotis parva)
The smallest abalone species, rarely growing beyond 45mm, the siffie is notable for the large hump that traces the spiral of its shell. Its shell is a mottled orange-brown, and its head has bright orange tentacles.
This species is found under rocks and in rock pools in the Southern Cape and parts of the Eastern Cape.
Courtesy of Gastropods.com
Venus ear siffie (Haliotis spadicea)
This abalone is ear-shaped, with a shell commonly stained with red blotches. It is a small abalone, rarely growing larger than 8cm.
The Venus ear lives in rocky crevasses along the coasts of the Southern and Eastern Cape, feeding on red algae.
Courtesy of Gastropods.com
Quekett's abalone (Haliotis queketti)
Quekett's abalone is similar in size and distribution to the spiral-ridged siffie, being slightly larger and occuring a bit further east along the South African coast.
It is a rare species, but easily identifiable by the prominent raised ridges along the edge of its shell and by its spirals.
Courtesy of Gastropods.com
Beautiful ear-shell (Haliotis speciosa)
This is a very unusual species of abalone, rarely observed. It has a smooth, mottled grey shell and is small, only growing up to 9cm.
It inhabits shallow waters on the coast of the Eastern Cape and KwaZulu-Natal.
What do abalone eat - and what eats them?
All abalone species eat algae, and mature adults prefer scraps of kelp. Abalone are quite lazy and prefer to remain in a small area and wait for scraps of kelp to drift by. However, they will move when there is a change in season or water quality, or when food is scarce - a change in their shell colour usually indicates a new food source.
Abalone will often stay in their own small territory waiting for scraps of kelp to drift by. Image courtesy National Geographic/Craig Foster
Juvenile abalone cannot grip the scraps of kelp, so they rely on films of bacteria, algae and micro-organisms on rocks for nourishment.
In nature, abalone are at risk of predation at all stages of their life. Their eggs and planktonic larvae are fed on by filter-feeders like barnacles, bivalves and shrimps.
Juvenile abalone hide in cracks or under the spines of Cape sea urchins during the day but need to forage at night - putting them at risk of predation by octopuses, sea stars, crustaceans, snails and durophagous (shell-swallowing) fish.
Adult abalone are at risk of predation by a few large predators, such as rays with crushing jaws and sea otters. However, humans pose the greatest threat to mature abalone and are responsible for its current population decline.
What's an abalone's love life like?
Abalone are "broadcast spawners", meaning their eggs and sperm are released into the ocean and fertilisation takes place in the water column. This spawning is synchronised by temperature, season or a full moon - different species use different indicators. A fully grown abalone can release tens of millions of eggs in a single spawn.
Eggs hatch into tiny larvae that swim freely in the water for a few weeks, using tiny hairs to propel themselves. Eventually, these larvae settle on the sea floor and shed these hairs - immediately beginning the secretion of a shell.
Image courtesy of Mendocino TV
Survival rates are very low, and it is estimated that fewer than one in 10 000 abalone survive to maturity (even before taking human threats into account).
A species at risk
WWF SASSI has placed abalone on the Red List, meaning you should not buy this species. Perlemoen takes eight to 10 years to reach "legal" fishing size in designated commercial zones. However, abalone grow slowly and can take up to seven years to reach sexual maturity - the regulations are simply unable to ensure that abalone have sufficient time to reproduce in the wild before being harvested. If a species cannot reproduce before being harvested, its numbers cannot recover.
Perlemoen poaching is rampant in disadvantaged coastal communities in South Africa, where it is seen as one of the only ways to escape poverty. Image courtesy Daily Voice
Additionally, abalone's small size and high value have led to prolific poaching. Fishing is poorly regulated and despite best efforts, there is little effective management of this species.
Abalone graveyards, like this one near Hout Bay, are often all that is left of an ecosystem after poachers indiscriminately shuck all perlemoen in sight from their shells. Image courtesy National Geographic/Craig Foster
Juvenile perlemoen depend on Cape sea urchins to survive - they follow the urchins around, hiding under their spines for protection from predators. An unprecedented influx of West Coast rock lobster to regions of the Cape has resulted in increased predation of these urchins, leaving the young perlemoen exposed.
This influx of rock lobsters, which previously only inhabited the West Coast and rarely rounded the Cape Peninsula, has not been thoroughly explained. However, increased pressure on the rock lobster population caused by water pollution and climate change is likely responsible for this migration, and is evident by the increasing numbers of "lobster walkouts". This relationship between kreef, urchins and perlemoen highlights the intricacies of ecosystems and how susceptible they are to damage by humans.
Abalone is also commercially farmed in South Africa - SASSI recognises this as a sustainable: commercially farmed abalone are on the Green list. Feel free to enjoy abalone as a meal, but ensure it is sourced from a sustainable aquaculture source. Abalone farmers in South Africa are cooperating to ensure that the gene pool of captive farmed perlemoen remains diverse - an important type of conservation if farmed abalone are ever needed to replenish the wild population.
We've written about abalone farming before - check out these baby blue jewels.
The threats facing abalone are not uniquely South African, nor are they limited to Haliotis midae. In the USA, overfishing of white abalone (Haliotis sorenseni) that started in the 1960s has done so much damage that despite 30 years of intensive conservation efforts, its numbers have not recovered and its extinction seems inevitable. Similar trends are seen in other large abalone species - pinto abalone, black abalone, green ormer, pink abalone and others are facing similar declines.
Inspired to do more to protect our oceans? Learn more about the Two Oceans Aquarium's conservation and research efforts - and find out how you can contribute today.