Common names: Abalone, South African abalone (Eng.); perlemoen (Afr.).
South African abalone, mostly known locally as perlemoen (from the Dutch meaning ‘mother-of-pearl’), is endemic to the shores of South Africa. This economically important species is highly utilised and has a high market value. It is therefore one of the most sought-after invertebrates in the country.
How to recognise abalone
Haliotis midae is one of five South African endemic abalone species. The others are Haliotis parva, H. spadicea, H. queketti and H. speciosa (Evans et al. 2004). They are marine snails that are associated with rocky areas.
Haliotis midae has a flattened, ear-shaped shell with a wide opening at the base – unlike their terrestrial snail cousins that have spiral shells (Attwood 2000). It also has a row of small holes through which water escapes after aerating the gills. South African abalone has a muscular foot running along the wide open base (Lyons 2011). The shell covers the dorsal part of the body leaving some fleshy parts protruding from the side.
They are the biggest abalones of the five indigenous species, growing to 230 mm in size (Van der Merwe 2009). Males and females can be told apart by looking at their gonads (reproductive parts); males have cream-coloured gonads while females have green-coloured gonads (Visser-Roux 2011).
Similar to terrestrial snails, South African abalone moves by creating a series of wave-like movements across the muscular foot, which propels them forward. They also use the foot for gripping on rocks (Attwood 2000).
South African abalone has a wide but patchy distribution. It is distributed along the coast of Port St. Johns in the Eastern Cape through to Saldanha Bay in the Western Cape (Rhodes 2013; Visser-Roux 2011).
South African abalone is generally found in shallow coastal waters and seems to prefer rocky surroundings (Van der Merwe 2009). Juvenile abalone associate themselves with sea urchins, Parechinus angulosus, which they depend upon for protection (Slabbert 2010).
Abalones in general are herbivorous (Makhande 2008) and feed mainly on kelp and red- and green algae. They catch floating or overhanging kelp by raising the front part of their body and extending the far end of their foot (Cloete 2008). Floating, overhanging kelp or algae that come into contact with the foot are trapped and fed on (Cloete 2008). If a large enough kelp is caught then the neighbours also join in and feed. Abalone farming usually alternates sea weeds with synthetic food as food sources (Francis et al. 2008)
Sex and life cycles
Reproduction in abalone is dioecious – that is, it occurs between male and female (Makhande 2008). During spawning males and females release reproductive cells through small breathing holes (Cloete 2008). As male and female reproductive cells interact, fertilisation takes place.
Wood and Buxton (1996) showed that the breeding season of South African abalone is between March and October, with spawning peaking between April and June. Temperatures have a large impact on larval development. High temperatures are associated with prevention or even termination of larval development, while low temperatures are associated with longer duration of the larval stage. The temperature must be warm, at around 18°C for South African abalone (Visser-Roux 2011).
After fertilisation, abalone goes through different developmental stages. At the juvenile stage, South African abalones start looking for areas where they can settle and be safe (Visser-Roux 2011). This can range from rocky areas to patching themselves to sea urchins until their shells become strong enough to protect them from most predators. According to Steinberg (2005), South African abalones are believed to live up to 30 years. They reach sexual maturity at around 20–25 mm shell width (Wood & Buxton 1996) or around seven years of age (Attwood 2000).
South African abalones live in groups. Attwood (2000) commented that this group lifestyle helps to increase the chances of success during breeding season.
THE BIG PICTURE
Friends and foes
Juvenile abalones associate themselves with sea urchins for protection. There is scientific evidence that population decline in sea urchins results in population decline in abalones (Makhande 2008). Rock lobsters predate mostly on small invertebrates including sea urchins (Cloete 2008). Octopus and eagle rays are also known to feed on juvenile abalones (Attwood 2000). The biggest threat to South African abalones is humans. Combined pressure of commercial harvesting and poaching have had a big impact, jeopardising the survival of wild populations (Edwards & Plaganyi 2008).
Abalones have high fecundity (reproduction rates), making them reproduce often and with many offspring (Wood & Buxton 1996). The high reproductive rate is believed to be responsible for the species’ survival, despite naturally small population numbers and the enormous impact of human activities on the species. Moreover, mutualistic relationships with poisonous and mostly spine covered species also provides some level of protection and increase their chances of survival.
Poorer world without me
Abalones feed on sea weeds and floating weeds, thus acting as their biological control (Hamer et al. 2010) and also helps with the cleaning of the ocean.
People & I
Abalones have long been used as a seafood resource around the world. In South Africa commercial use of Haliotis midae started around 1980 (Franchini et al. 2011). Because of how highly sort after South African abalone is, it became highly valued and economically important, especially in the aquaculture industry (Visser-Roux 2011). It is the most exported species in aquaculture, and in 2008 constituted 81% of the total income of national aquaculture (Britz et al. 2009). This is because of the high demand in Asian countries, where almost all exports go to (Steinberg 2005).
South African abalone, together with other marine life that serves as seafood, have been found to have an increasingly high medical impact – causing food allergies – although at the moment it impacts only a small population (Lopata & Jeebhag, 2007). It induces allergic reactions and asthma attacks. Care must be taken if ever one wants to enjoy a plate of South African abalone for the first time.
Conservation status and what the future holds
The increasing pressure put on South African abalone by both legal and illegal harvesting had led to the banning of abalone harvesting and listing thereof on CITES in Appendix 3 and in the National Environmental Management: Biodiversity Act 10 of 2004 (NEMBA). They were then removed from both CITES and NEMBA because of pressure from the fishing industry (Raemaekers et al. 2011).
South African abalone hasn’t been fully assessed, although a few assessments done by researchers show the studied populations to be declining (UNEP-WCMC, 2010). The fact that they have a slow growth rate makes them vulnerable to impacts of overharvesting (Attwood 2000). Immediate full assessments and research on wild populations are needed so proper planning for protection and sustainable use can be done. Current management strategies put in place seem to have little effect in protecting this species, and continued pressure and unsustainable use seem to persist (Raemaekers et al. 2011).
Haliotis midae is one of five South African endemic abalone species. The others are Haliotis parva, H. spadicea, H. queketti and H. speciosa (Evans et al. 2004).
Species: H. midae Linnaeus, 1758.
References and further reading
- Visser-Roux, A. 2011. Reproduction of the South Africa abalone, Haliotis midae. PhD Dissertation, University of Stellenbosch, Stellenbosch, South Africa.
- Cloete, Y.C. 2008. The characterization of intracellular protozoan parasite infecting the digestive gland of abalone, Haliotis midae. MSc Dissertation, University of Johannesburg, Johannesburg, South Africa.
- Wood, A.D. & Buxton, C.D. 1996. Aspects of the biology of the abalone, Haliotis midae Linneaus, 1758, on the east coast of South Africa. South African Journal of Marine Science 17(1): 69–78.
- Steinberg, J. 2005. The illicit abalone trade in South Africa. Institute for Security Studies paper 105.
- Attwood, C. 2000. Coastal and Marine Life – Animals: Invertebrate. https://www.capetown.gov.za/en/EnvironmentalResourceManagement/publications/Documents/Coastcare%203B-Invertebrates.pdf. [Accessed 19 November 2014].
- Evans, B.S., Sweijd, N.A., Bowie, R.C.K., Cook, P.A. & Elliott, N.G. 2004. Population genetic structure of the perlemoen Haliotis midae in South Africa: evidence of range expansion and founder events. Marine Ecology Progress Series, 270: 163–172.
- Lyons, J. 2011. Identification and partial characterization of the HSP70 gene of the South African abalone, Haliotis midae. MSc Dissertation, University of Cape Town, Cape Town, South Africa.
- Van der Merwe, E. 2009. Toward best management practices for the growth of the abalone, Haliotis midae Linnaeus, on a commercial South African abalone farm. MSc Dissertation, University of the Western Cape, Cape Town, South Africa.
- Franchini, P., Van der Merwe, M. & Roodt-Wilding, R. 2011. Transcriptome characterization of the South African abalone, Haliotis midae, using sequencing-by-synthesis. BMC Research Notes, 4:59. http://www.biomedcentral.com/1756-0500/4/59. [Accessed 6 August 2014].
- Francis, T.L., Maneveldt, G.W. & Venter, J. 2008. Growth of market-size abalone (Haliotis midae) fed kelp (Ecklonia maxima) versus a low-protein commercial feed. African Journal of Aquatic Science 33(3): 279–282.
- Makhande, E.D. 2008. Growth of the South African abalone (Haliotis midae) on three diets, under commercial conditions. MSc dissertation, Nelson Mandela Metropolitan University, Port Elizabeth, South Africa.
- Slabbert, R. 2010. Identification of growth-related quantitative trait loci within the abalone, Haliotis midae, using comparative microsatellite bulked segregant analysis. PhD Dissertation, University of Stellenbosch, Stellenbosch, South Africa.
- Rhode, C. 2013. Signatures of selection in natural and cultured abalone (Haliotis midae): a population genomics study. PhD Dissertation, University of Stellenbosch, Stellenbosch, South Africa.
- Hamer, P.A., Jenkins, G.P., Womersley, B.A. & Mills, A. 2010. Understanding the ecological role of abalone in the reef ecosystem of Victoria. Project No. 2006/040, Fisheries Research and Development Corporation and Department of Primary Industries, Victoria.
- Edwards, C.T.T & Plaganyi, E.E. 2008. Participatory assessment of the South African abalone resource and its impact on predicted population trajectories. South African Journal of Science 104: 185–191.
- Britz, P.J., Lee, B. & Botes, L. 2009. AISA 2009 Aquaculture Benchmarking Survey: Primary Production and Markets. AISA report produced by Enviro-Fish Africa (Pty) Ltd. 117p.
- Lopata, A.L. & Jeebhay, M.F. 2007. Allergy and asthma to indigenous seafood species in South Africa. Current Allergy and Clinical Immunology 20(4): 196–200.
- UNEP-WCMC. 2010. Review of Haliotis midae. UNEP-WCMC, Cambridge.
- Burgener, M. 2014. The illegal trade in South African abalone (Haliotis midae). TRAFFIC East/Southern Africa. http://www.stopillegalfishing.com/doc/publication/eng/illegal_trade_in_SA_abalone.pdf. [Accessed 6 August 2014].
- Raemaekers, S., Hauck, M., Burgener, M., Mackenzie, A., Maharaj, G., Plaganyi, E.E. & Britz, P.J. 2011. Review of the causes of the rise of the illegal South African abalone fishery and consequent closure of the rights-based fishery. Ocean and Coastal Management 54: 433–445.
Author: Mahlatse Kgatla