Black abalone (Haliotis cracherodii)
|Size||Length: 20 cm (2)|
The black abalone is classified as Critically Endangered (CR A4e) on the IUCN Red List 2004 (1).
The exterior of this marine gastropod mollusc’s shell varies in colour from dark blue through dark green to black (2). It is smooth with little algal growth, and has five to nine open pores in a line along the left side of the shell. The rear of the shell is spiralled, and the mantle, foot and tentacles are black (3). The interior of the shell is pearly with pink and green iridescence (2).
The black abalone is found on the coasts of Baja California, Mexico and California, USA (1).
Inhabits rocky substrates in intertidal waters, from the high tide line to a depth of 5 m (1).
This sessile mollusc uses its foot to clamp tightly to a rock, where it feeds on algal matter scraped from the rock surface, and catches drifting algae with its tentacles. Juveniles tend to reside in crevices to reduce their risk of predation, but the larger adults will move out onto rock surfaces. They may still be preyed upon by fish and otters (1).
Between three and seven years old, the black abalone will begin to reproduce. In a perfectly synchronised release of eggs and sperm amongst all the abalones in one area, fertilisation occurs, resulting in tiny free-swimming larvae. After 15 days, the larvae metamorphose into their adult form, develop a shell and settle onto a rock. They are thought to be able to live for between 25 and 75 years, and will begin to reproduce between three and seven years (1).
The black abalone has suffered a serious decline since 1985 due to a disease known as withering syndrome, which spread through the California Channel Islands between 1985 and 1992. It causes wasting of the foot muscle, preventing the abalone from properly adhering to a rock, causing the abalone to become discoloured, lose weight and die. Population losses in each area ranged from 20% to total (1).
Other threats include coastal development for residential areas, harbours and waste discharges, compounded by commercial and recreational fishing of the black abalone (1).
All abalone fisheries in California are managed by the California Department of Fish and Game, which restricts the size of abalones caught, and the season in which harvesting can take place. In Mexico, there is a total allowable catch limit for black abalones. The black abalone is a candidate species on the US Endangered Species Act, and whilst this could be beneficial in the future, it does not currently give the species any legal protection (1).
An American-Mexican fishery authority alliance has been proposed as a means to develop a restocking programme to restore black abalone populations. There is to be a public appeal for funding, which would allow an investigation into the causes of withering syndrome (1).
For further information on this species see the IUCN Red List 2004:
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- Alga: a collection of taxonomically unrelated groups that share some common features but are grouped together for historical reasons and for convenience. They are of simple construction, and are mainly photoautotrophic, obtaining all their energy from light and carbon dioxide, and possess the photosynthetic pigment, chlorophyll A. They range in complexity from microscopic single cells to very complex plant-like forms, such as kelps. Algal groups include blue-green algae (cyanobacteria), red algae (rhodophyta), green algae (chlorophyta), brown algae and diatoms (chromista) as well as euglenophyta.
- Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
- Mantle: in molluscs, a fold of skin that encloses a space known as the mantle cavity, which contains the gills. The mantle is responsible for the secretion of the shell.
- Metamorphosis: an abrupt physical change from the larval to the adult form.