About Abalone

 Distribution

Biology

Environment

References

DISTRIBUTION

World Distribution

Abalone are found along most rocky shores in tropic and temperate waters. Most are encountered in the shallow subtidal between sea level and 30 m depth. There are 56 currently described species that are distributed world-wide. There are no abalone species of global distribution. The largest areas of distribution are inhabited by some Indo-Pacific taxa. The most widespread taxa are Haliotis clathrata (East Africa to Samoa), H. asinina and H. planata (Thailand to Fiji), and H. ovina (Maldives to Tonga). All other species have much more restricted ranges.

Four discrete regions of endemism can be identified. In South Africa five species are encountered, in New Zealand three, the western North American coast harbors six species, and Australia has nine endemics. Within these areas the overlap between widespread species varies from none in western North America and New Zealand, to slight in South Africa, to substantial in Australia.

The most well supported hypothesis for the origin of the abalone puts their beginnings in a generalised Indo-Pacific region. The highest present day diversity of the family is found in the Indo-Malayan area and may be the centre of radiation.

Daniel Geiger has an excellent site with distribution maps of all the 56 described species of abalone worldwide.

Go to Daniel’s site: http://www.sbnature.org/geiger/ABMAP/worldmap.html

Australian Distribution

There are 18 species of abalone described for Australian waters, and of these ten are endemic. In northern Australia several species of tropical Indo-Pacific distribution can be found along the warmer coasts (i.e., H. asinina, H. clathrata, H. ovina, H. rubigosa, H. squamata). However, those species that seem to prefer more temperate waters are endemic to the Australian continent (H. brazieri, H. coccoradiata, H. cyclobates, H. elegans, H. laevigata, H. roei, H. rubra, H. scalaris, H. semiplicata).

Daniel Geiger’s site has distribution maps for all the Australian species of abalone.

Go to Daniel’s site: http://www.sbnature.org/geiger/ABMAP/Australia.html

BIOLOGY

Body Structure

Abalone are marine snails belonging to the Phylum Mollusca, in the Class Gastropoda, which are molluscs with single shells, or no shell at all, that move by means of a broad muscular foot. It is the foot of the abalone that has commercial value as a food, particularly to many Asian people. Gastropods show some degree of torsion (a twisting of the body during larval development). As members of the Subclass Prosobranchia, abalone undergo torsion during the veliger larval stage so that the mantle cavity and gills come to lie at the front of the body, and the nervous system is twisted into a figure eight.

As members of the Order Archaeogastropoda, they have no siphon or proboscis and have gills with filaments on both sides of the gill axis (bipectinate). Family Haliotidae, the abalone, have a visceral mass (organs) and shell that are markedly flattened, and the spire is greatly reduced. The shell has a row of holes through which the respiratory current exits, carrying also urine, and sometimes gametes. Faeces are expelled under the shell, near the head. In situ, the only body parts visible are the epipodium and the head structures. The epipodium is a fleshy girdle surrounding the foot and projecting below the margin of the shell. The head structures comprise the eyes, cephalic tentacles and the snout. The eyes are simple cup-eyes without a lens located on short and movable eye stalks. The cephalic tentacles can be either strongly contracted (to the length of the eye stalks) or fully distended when they can reach about one third of the body length. The snout is found between the two tentacles and contains the mouth opening.

Abalone are nocturnal herbivorous snails, eating seaweeds that drift past by catching them with the front, highly extendable part of their foot. They are slow feeders, spending much of the night searching and consuming food. Pieces of seaweed that are caught are held down with the foot and drawn into the mouth using a ribbon of rasping teeth, called a radula. The radula is a chitinous band with rows of attached teeth. The best way to see the radula in use is to observe an abalone attached to the wall of a glass aquarium that has a film of algal growth. The radula can be observed within the mouth rasping against the glass using short strokes that remove the algae and scoop it into the mouth.

Commercial species are long lived and slow growing, reaching between 15 and 30 mm in their first year and 10 cm in about 3-6 years according to species and locality. Large specimens are estimated to be between 10 to 50 years old. Abalone have separate sexes and release their gametes into the sea (broadcast spawning) where fertilisation takes place. Spawning occurs mostly during the summer months and multiple spawnings during one season are possible. Spawning cues include elevated water temperature, high wave action, photoperiod, lunar cycle, and presence of abalone gametes. Some species (H. scalaris, H. roei) spawn throughout the year. Fertilisation of gametes from the same species is facilitated by fertilisation proteins in the sperm head that are species-specific. Fertilised eggs develop rapidly (about one day) into free swimming trochophore larvae. Larvae develop to become shelled veligers with a foot, operculum, eye spots, mouth and radula. At the end of the free swimming period (about 1 week) larvae fall to the bottom and explore the rocky substrate. If the surface is suitable for settlement (abalone prefer to settle on encrusting coralline algae), larvae lose the ability to swim and they crawl over the surface and start feeding. Small juveniles graze on microscopic plants or diatoms (and the substances they exude) and ingest and utilise a range of bacteria (including those growing on abalone mucous) and microscopic organisms.

Diet

All southern Australian species prefer red algae and avoid brown algae when given a choice (Shepherd, 1973; Shepherd and Steinberg, 1992; Fleming, 1995a). Algal palatability between H. rubra and H. laevigata is remarkably similar. The following table summarises the average consumption of red, green and brown algae by H. laevigata and H. rubra when fed 58 algae from southern Australian waters (Hone and Fleming, unpub. man.).

Both species consume more of the red algal species than the green or brown species. The overall order of algal consumption for both species is reds>greens>browns. These dietary preferences are in marked contrast to those of abalone species from the northern hemisphere which generally prefer and grow fastest on brown algae that contain low levels of tannin-like chemicals (polyphenolics) (Steinberg, 1989). In contrast, most of the brown algal species that occur in Australia have high levels of polyphenolics which deter grazing by abalone (Shepherd and Steinberg, 1992). Thus, Australian abalone cannot grow at commercial growth rates on any of the brown algae native to Australia. In addition, Australian abalone generally grow faster on a diet of red algae (Fleming, 1995a; Hone, 1992) which are more readily digested (Foale and Day, 1992; Fleming, 1995b). A mixed diet consisting predominantly of numerous species of red algae produces the highest growth rates (Fleming, 1991; Hone, unpub. data).

Many studies have examined the gut contents of animals in the field in an attempt to determine the preferred diet of Australian abalone (Shepherd, 1973; Sanders, 1981; Shepherd and Cannon, 1988; Wells and Keesing, 1989), as it is assumed that an animal consumes more of those foods that promote fast growth rates. Generally, Australian abalone were found to consume red algae when available, but subsist on a diet of brown algae when feed availability was low. Shepherd (1973) investigated the diet of H. laevigata, H. rubra, H. roei, H. scalaris and H. cyclobates at two reefs in South Australia and reported that, in general, abalone species living in the same habitat have similar diets, with only minor differences apparent when preferred red algae were scarce. Over a 12 month period abalone consumed 45-80% red algae, 7-15% brown algae (except H. cyclobates which consumed 38%) and <5% green algae. Abalone consumed more of the preferred, red algal species during winter and more of the less preferred, brown algal species during summer. At the site where animals fed extensively on epiphytes attached to seagrasses, the latter contributed 10-33% to the diet, although it has very poor nutritional value (Fleming, unpub. data). Carblis (1972) also found large quantities of the seagrass Posidonia australis in the gut of H. rubra from Jervis Bay, NSW. Animals were presumably consuming the abundant epiphytes that grow seasonally on this plant. These epiphytes would be digested rapidly, leaving only the indigestible seagrass identifiable in the gut contents. Clearly, the range and quantity of algal species that contribute to the diet on a particular reef at any one time is dependent on the composition of the drift algae that reaches the reef. Thus, diet composition differs considerably from reef to reef and from season to season.

Interestingly, very little information is available on the type of red algae consumed in the field due to the rapid rate at which it becomes unrecognisable in the gut (Foale and Day, 1992). Red algal species found in the guts of H. rubra sampled from Port Philip Bay, Victoria included; Acrosorium sp., Gelidium pusillum, Lophurella sp. and Polysiphonia sp. (Sanders, 1981). Brown algal species consumed by H. rubra in Port Philip Bay included phenolic-poor species (Shepherd and Steinberg, 1992), such as Macrocystis angustifolia and Lobospira bicuspidata, as well as Dictyota dichotoma and Zonaria sinclairii. The green algae Ulva rigida, Enteromorpha sp. and Cladophora glomerata also contributed to the diet (Sanders, 1981).

Water movement affects the feeding of H. laevigata and H. rubra as they are dependent on currents to supply algal drift (Shepherd, 1973). These species feed best in conditions of moderate water movement but poorly if the water is too calm or too rough. Water movement elicits a characteristic feeding response; while waiting to catch drifting algae the abalone elevates its shell above the substrate, sometimes extending its tentacles and the forepart of the foot as well. It maintains this posture until it catches a pieces of drift seaweed with its foot, often showing surprising dexterity in doing so (Shepherd, 1973). Hingham and Hone (1996) tested the effect of water movement between 0.7-5.8 cm/sec on feed consumption by 30 mm H. laevigata. They found that consumption increased linearly with flow rate.

Movement

Abalone move slowly and often do not move from one location for many months, or even years. The locomotory habits of southern Australian abalone are nocturnal and associated with feeding (Shepherd, 1973; Fleming, 1996). Species with a cryptic habitat (H. roei and H. scalaris) graze actively at night, but those in an open habitat (H. laevigata) catch drift seaweed and move little or not at all. H. rubra falls into one group or the other according to its habitat. Shepherd (1973) reported that H. rubra was strictly nocturnal, moving out after dark to graze on algae and returning, but not always to the same crevice, before morning. The movement of H. rubra in deeper caves is more complex. Here a size hierarchy exists where large animals occupy places near the cave mouth and small ones live further back in the cave. Smaller animals appear to move out towards the mouth of the cave to capture drift algae but large animals already there do not move. It is considered that the presence of drift seaweed and an underwater surge both stimulate movement by H. rubra. In other areas Shepherd (1973) did not observe any movement of H. rubra. Shepherd (1973) reported that most H. laevigata individuals remained on the same rock for months at a time, and some did not moved during a 2 year period. Shepherd (1986) found that movement was related to crevice availability at one site. If there were no crevices free the animal kept moving until it found a crevice. Overall, it is probable that the extent of movement of an abalone is dependent on food supply and that in the presence of abundant drift algae, abalone cease moving altogether.

Reproduction

H. rubra and H. laevigata become sexually mature in the wild at about 3-4 years of age and between 75 and 120 mm, depending on locality (Shepherd and Laws, 1974). In contrast, abalone raised in culture can develop gonads in their second year (about 25 mm). As abalone get larger the number of eggs produced increases exponentially (see figure below), with 100 mm animals producing about 0.5 million eggs and 150 mm animals producing about 3 million eggs. Shepherd et al. (1992a) noted marked variation in fecundity between sites and attributed the variation to differences in food supply, water movement and habitat, although genetic effects could not be excluded. Fecundity also varies between individuals, between populations, and even between years due to differences in food availability (Shepherd et al., 1992a).

The reproductive cycle of abalone is primarily influenced by seawater temperature and the amount of food eaten, and to a lesser extent by the photoperiod. In a South Australian population of H. laevigata studied by Shepherd and Laws (1974) the period of maximum gonad growth coincided with an abundant food supply during winter (from May to October). Spawning began in October and lasted through summer and autumn. Fully spent gonads indicative of complete spawning occurred from January until June. Recovery of the gonad was rapid during winter. This pattern was similar at each site and for each year. The authors also found that gametogenic changes in H. laevigata correlated more closely with changes in the amount of food eaten than with sea temperature changes alone.

The breeding cycle of H. rubra has shown perplexing variability in the timing and duration of its spawning season at different places. At one site in South Australia, Shepherd and Laws (1974) found spawning occurred during spring or early summer (October to January) and again during autumn (March to June). The majority of animals had spawned out completely by the end of autumn. Spawning was poorly synchronized; peaks occurred in spring and autumn with possibly minor spawning activity in other seasons. The authors proposed that individuals of H. rubra at this site had an annual reproductive cycle in which gametes are released in small amounts over an extended season. At another site studied by Shepherd and Laws (1974) the annual reproductive cycle of H. rubra involved a single period of gametogenesis and a single spawning season. The onset of spawning was positively correlated with the decline in sea temperature after the summer maximum, while the correlation with the amount of food eaten was slight. In contrast, a Tasmanian population of H. rubra was reported by Harrison and Grant (1971) to spawn during spring, while McShane et al. (1986) reported a single spawning period at a Victorian site from late spring over the summer months and, in some cases, into autumn. At another site in Victoria, gametes were released throughout the year. McShane et al. (1986) found no correlation between gametogenesis and a change in water temperature and proposed that a suite of environmental factors act together to determine reproduction in H. rubra. However, our observations of wild abalone has shown two patterns. Firstly, when weather conditions are relatively constant and mild, abalone will serially spawn during the reproductive season. Secondly, if peak stress events occur, in the form of extreme weather, all abalone near condition will spawn.

A knowledge of spawning cycles and how these relate to local environmental conditions is essential for farmers collecting broodstock. By understanding how the wild stocks vary in their reproductive condition over time and from site to site, it is possible to stagger the collection of broodstock over the season. More importantly, by knowing which local stocks are early spawners, it is possible to commence hatchery operations early and take advantage of the first summer to maximize the opportunity for high growth rates, which are temperature related. This means that the abalone are a good size leading into their first winter, which increases the chance that they will continue to grow during the first winter rather than slow to a near zero growth rate.

ENVIRONMENT

Habitat

Habitat of Juveniles

Predators and Pests

Habitat

Each of the six species of southern Australian abalone occupies a distinctive microhabitat on rocky reefs, although several species may occur together in a given habitat (Shepherd, 1973). H. laevigata and H. rubra live in distinctly different habitat types and the different habitat preferences of these species should be considered when designing a culture system for them. H. laevigata occurs in open habitat, generally of two types; offshore on rocks of low relief at depths of 10-30 m, often in the lee of islands, headlands, or reefs and in very rough water at the base of steeply sloping cliffs of granitic rock, usually on the sides of gutters or clefts in the rock face at depths of 10-25 m. In more sheltered places it occurs on rocks near the sand at lesser depths. In both habitats H. laevigata rests preferentially in places where drifting seaweed is likely to settle or be carried past. H. rubra hides in crevices, caves, or vertical faces in low light conditions from 1-2 m depth to about 10 m depth, and rarely to 25 m. It occurs on rock faces on both rough-water and sheltered coasts where there is suitable habitat. Both species are sedentary, but may make local movements (usually less than 10 m) in search of food.

Habitat of Juveniles?

Young abalone in southern Australia change their microhabitat as they grow. Abalone from 2 to 10 mm occur on encrusting coralline red algae on the sides of boulders and the upper sides of rocks under boulders (Shepherd, 1973). Juvenile abalone consume benthic diatoms, bacteria and mucous, all of which occurs on the surface of the coralline algae. At about 10 mm long each abalone species moves to a preferential cryptic microhabitat under boulders. Microhabitat segregation is partially achieved through preferred depth ranges, although some overlap in depth range occurs between species. Young abalone move out at night to graze on the upper surface of the boulder, returning before morning.

Predators and Pests

The predators of abalone include wrasse, stingrays, crabs, molluscs, and starfish. Crevices, caves and cavities under boulders provide a refuge in space from predators for H. roei, H. rubra, and H. scalaris and juveniles of other species, which appear to be confined to these places by the activity of their predators, except during nocturnal feeding excursions (Shepherd, 1973).

Pests of abalone include the mudworm Polydora websteri and the parasite Perkinsus olseni. Mudworm burrow through the shell forming a blister in it. Extreme infection can severely retard growth and kill the animal. Mudworm infestations in commercial farming operations usually occur when abalone are grown in environments characterised by silt or accumulated faecal matter. The precursor for the initial settlement of mudworm in these situations appears to be silt on the abalone shell.

Perkinsus is predominantly a South Australian parasite that infests the foot causing blisters. Not much is known about the infection mechanisms of Perkinsus. As a precautionary method, farmers should be aware of locations that are known to have wild abalone infested with Perkinsus and these should be avoided. Only two locations are known to have persistent, high levels of infection of Perkinsus. These are Neptune Island, Thorny Passage (south of Port Lincoln) and the bottom eastern tip of Yorke Peninsula.

REFERENCES

References

Carblis, P.Z.H. (1972).

Preliminary investigations into the biology of the abalone, Haliotis ruber, in New South Wales waters. Honours Thesis, Sydney University, Australia. 114pp.

Fleming, A.E. (1991).

The nutritional biology of the black lip abalone, Haliotis rubra. Ph.D. Dissertation, Melbourne University, Australia. 99pp.

Fleming, A.E. (1995a).

Growth, intake, feed conversion efficiency and chemosensory preference of the Australian abalone, Haliotis rubra. Aquaculture, 132: 297-311.

Fleming, A.E. (1995b).

Digestive efficiency of the Australian abalone Haliotis rubra in relation to growth and feed preference. Aquaculture, 134: 279-293.

Fleming, A.E. (1996).

Effects of the physical aspects of artificial feed on abalone feeding behaviour. In: Proceedings 3rd Annual Abalone Aquaculture Workshop. 16-18th August 1996, Port Lincoln, South Australia.

Foale, S. and Day, R. (1992).

Recognizability of algae ingested by abalone. Australian Journal of Marine Freshwater Research, 43: 1331-1338.

Harrison, A.J. and Grant, J.F. (1971).

Progress in abalone research. Tasmanian Fisheries Research, 5: 1-10.

Hingham, J. and Hone, P.W. (1996).

Preliminary results on the effect of water movement on feed consumption. In: Proceedings 3rd Annual Abalone Aquaculture Workshop. 16-18th August 1996, Port Lincoln, South Australia.

Hone, P.W. (1992).

Preliminary results of artificial diet trials. In: Proceedings Biotechnology Aquaculture Workshop: Abalone Artificial Diets, 15th July 1992, Department of Primary Industries (Fisheries), Aquaculture Research Section, Adelaide, South Australia.

McShane, P.E., Beinssen, K.H.H., Smith, M.G., O'Connor, S. and Hickman, N.J. (1986).

Reproductive biology of blacklip abalone Haliotis rubra Leach from four Victorian populations. Technical Report No. 55, Victorian Ministry for Conservation, Forests and Lands, Marine Science Laboratories, Australia.

Sanders, S. (1981).

Feeding ecology of blacklip abalone Haliotis rubra Leach 1814 at two locations in Port Phillip Bay, Victoria. Honours Thesis, Melbourne University, Australia. 28 pp.

Shepherd, S.A. (1973).

Studies on southern Australian abalone (Genus Haliotis). I. Ecology of five sympatric species. Australian Journal of Marine Freshwater Research, 24: 217-257.

Shepherd, S.A. (1986).

Movement of the southern Australian abalone Haliotis laevigata in relation to crevice abundance. Australian Journal of Ecology, 11: 295-302.

Shepherd, S.A. and Cannon, J. (1988).

Studies on southern Australian abalone (Genus Haliotis). X. Food and feeding of juveniles. Journal of Malac. Society Australia, 9: 21-26.

Shepherd, S.A. and Laws, H.M. (1974).

Studies on southern Australian abalone (Genus Haliotis). II. Reproduction of five species. Australian Journal of Marine Freshwater Research, 25: 49-62.

Shepherd, S.A. and Steinberg, P.D. (1992).

Food preference of three Australian abalone species with a review of the algal food of abalone. In: S.A. Shepherd, M.J. Tegner, and S.A. Guzman del Proo (Editors). Abalone of the World: Biology, Fisheries and Culture. Blackwell Scientific Publications, Oxford, pp. 169-181.

Shepherd, S.A., Godoy, C. and Clarke, S.M. (1992a).

Studies on southern Australian abalone (Genus Haliotis). XV. Fecundity of H. laevigata. Journal of Malac. Society Australia, 13: 115-121.

Steinberg, P.D. (1989).

Biogeographic variation in brown algal polyphenolics and other secondary metabolites: comparison between temperate Australasia and North America. Oecologia (Berl.), 78: 373-382.

Wells, F.E. and Keesing, J.K. (1989).

Reproduction and feeding in the abalone Haliotis roei Gray. Australian Journal of Marine Freshwater Research, 40: 187-197.