Abalones at risk: A global Red List assessment of Haliotis in a changing climate

assessments of marine molluscs including 1047 from the taxonomic class Gastropoda, although 60% of these are of one family—Conidae, the cone snails [31, 32]. To place this in context, 74% of all fishes, 85% of reptiles, 90% of mammals, 92% of amphibians and 100% of birds have been assessed (www.iucnredlist.org/resources/summary-statistics). In 2003 and 2006 respectively, just two abalone species had been assessed for the Red List: H. cracherodii and H. kamtschatkana, both from Pacific North America. We assessed the cur- rent status and extinction risk of all 54 abalone species globally using IUCN Red List criteria. We explore each species’ distribution, current and projected threats from exploitation, poach- ing, environmental stress and ecological disruption. Our aim is to provide data in support of conservation measures for those species at the greatest risk of extinction over the short to medium term to inform climate smart restoration planning and action. Abalones Abalones are of the family Haliotidae, with a single genus, Haliotis, the etymology of which is from the Greek for sea-ear, reflecting its aural form. The name abalone derives from the Amer- ican Spanish abulón which in turn is a corruption of aulon in Rumsen, an Indigenous lan- guage, now extinct, of Monterey Bay, California [33]. Abalones first appear in the Late Cretaceous although the fossil record is poor with extended periods without evidence until their reappearance in the late Eocene, and then with greater frequency from the Late Miocene

to the present [34]. Abalones occur primarily in temperate regions although some species are found in tropical seas. They most often live in shallow, rocky, sublittoral waters between the subtidal and 30 m depth, although there are exceptions: H. pourtalesii for example, occurs from the Carolinas south to Brazil at 35 m to 350 m depth [34, 35]. Abalones have been impor- tant to Indigenous peoples for millennia [36]. Today they are of national and international commercial importance, primarily as a food delicacy but also for the exquisite nacre lining their shells which is used for jewellery and mother-of-pearl inlay in marquetry. Although it is normally the larger species that are consumed, there are instances of smaller species also find- ing favour including H. ovina, the sheep’s ear abalone at 80 mm and H. asinina, the donkey’s ear abalone at 100 mm. These tropical species, known as cocktail-size abalones, occur across the Indo West Pacific [37]. Abalones also fulfil an important ecological function in grazing on algae enabling open areas of benthic crustose coralline pavement suitable for the recruitment of abalones and other species [38]. Although abalones are generally small to medium in size, i.e. less than 100 mm, some are particularly large such as H. gigantea at 233 mm, with the current record held by a red abalone (H. rufescens) from Pacific North America at 313 mm taken by John Pepper [39]. Depending on species, abalones may be oval to rounded with generally three or four whorls and a small flat

spire. Shells range from smooth to those with protruding sculptured elements including ridges, bumps and striations [34]. The most distinguishing feature of all abalone species is a row of multi-functional holes around the margin of the anterior, used in the respiration of water from the gills, release of faeces, and expulsion of gametes into the water column [34]. The first hole appears in juveniles of 1 to 3 mm length and then they increase in number, with new ones appearing from the anterior margin as the abalone develops. Older holes towards the posterior are sealed by the mantle such that only the most recent holes are open at any point in the abalo- ne’s life. The number of open holes does not seem to be consistent to any species but are typi- cally five or six but sometimes more [34]. Abalone shell has exceptional tensile strength [40, 41] with practical applications in materials research including bone tissue engineering [42]. Although abalones are found across the globe (excluding polar regions), there are some notable voids. For example, although occurring along the Pacific coast of North America from PLOS ONE Abalones at risk: A global Red List assessment of Haliotis PLOS ONE | https://doi.org/10.1371/journal.pone.0309384 December 23, 2024 3 / 25