Kenneth A. Hayes and Norine W. Yeung
In the second installment of our updates on the status of the Hawaiian land snail fauna we are covering the two most species rich families represented in Hawaii, the Amastridae (Figure 1A-E) and Achatinellidae (Figure1F-J). Both families belong to the informal group Orthurethra within the Stylommatophora (Bouchet and Rocroi 2005), and together represent 71% of the recognized Hawaiian land snail diversity. The Achatinellidae, specifically species within the subfamily Achatinellinae, are probably among the more well-known of the two owing to the fact that all 41 species of the genus Achatinella were listed as endangered under the United States Endangered Species Act (ESA) in 1981 and have received considerable attention and conservation funding since. Recently, several species from other genera within the Achatinellinae were listed as Candidate Species, but no other Hawaiian land snail species are officially recognized as endangered or threatened by either the IUCN or the United States Fish and Wildlife Service. Part of the efforts of our ongoing research is to bring the plight of the remaining snail fauna to light, so what is left may be saved.
The Amastridae are less well known despite being the only extant family of plants or animals endemic to the Hawaiian Islands, and being the largest family of Hawaiian land snails in terms of numbers of species and size. Currently, none of the Amastridae are protected under the ESA, and only 33 are listed as extinct on the IUCN Red List (Régnier et al. in press). But like the Achatinellidae they have suffered from extraordinary rates of extinction, but have yet to receive the considerable funding or research attention needed to protect them. Solem (1990) and others (e.g. Zimmerman 1948) emphasized that endemism at the family and subfamily levels among the Hawaiian snail fauna notably set them apart from all other native Hawaiian animal groups. Not even the extraordinary radiation of terrestrial arthropods can lay claim to endemism at this level. There were 325 amastrid species belonging to eight genera divided into two subfamilies, the Amastrinae (Figure 1 A-D) and Leptachatininae (Figure 1E), although more than 85% of the species are in either the genus Amastra or Leptachatina (Cowie et al. 1995). The family also includes the largest of all Hawaiian land snails, Carelia turricula, which reached 80 mm in shell height (Figure 1D). Unfortunately, Carelia turricula and more than 95% of its kin, such as the smallest T. rex (Tropidoptera rex; Figure 1C), are now thought extinct (Régnier et al. in press). While our surveys revealed some surprises, like finding two species on Kauai (Figure 1E) and one on Maui that were thought extinct, our assessment of the Amastridae has only confirmed the dire predictions by most. However, in the shadow of such gloomy results, there is hope, which comes in the form of Chung’s (1986) and colleague’s successful captive rearing efforts of several species of amastrids, some no longer found in the wild. While these efforts have not been undertaken at the scale or with the rigor needed to recover wild populations, they do offer the possibility of one day doing so if sufficient long term funding can be secured.
Subfamilies: Amastrinae and Leptachatininae
Number of recognized species: 325
Number of species found in recent surveys: 14
Historical distribution: Kauai, Oahu, Maui, Lanai, Molokai, Hawaii, Niihau, Kahoolawe, Northwest Hawaiian Islands (NWHI)
Current distribution: Kauai, Oahu, Maui
Conservation status: Endangered
The second most diverse Hawaiian land snail family, the Achatinellidae, comprising 324 species across the Pacific, with 64% (209) of these in the Hawaiian Islands, and three species on islands in the Indian Ocean (Cooke & Kondo 1960, Cowie et al. 1995). The Five of the seven subfamilies (Pacificellinae, Tornatellininae, Tornatellidinae, Tekoulininae, Elasmatininae; Bouchet et al. 2005) are distributed across the range, with the latter two endemic primarily to French Polynesia and the Cook Islands. The other two subfamilies (Achatinellinae, Auriculellinae; Figure 1F and G) are endemic to Hawaii (Cooke & Kondo 1960, Cowie et al. 1995), and Pacificellinae, Tornatellidinae and Tornatellininae (Figure 1H-J) are also represented in Hawaii. All but one Hawaiian achatinellid species are endemic (Cowie et al. 1995). Of notable significance, is that the biogeographical and morphological patterns of this family have contributed significantly to the development of evolutionary theory, particularly fundamental ideas related to the founder effect, genetic drift and speciation (Gulick 1905, Carson 1987). Unfortunately, most opportunities to continue such studies with this fauna have been lost to extinction, but not all.
The charismatic Achatinellinae (Figure 1E) have received far more conservation-focused research and attention than other native Hawaiian land snails, including other achatinellids (Figure 1G-J), and their remains significant opportunities to study and conserve the remaining 10 species, most of which are in captivity. However, because of their protected status and the substantial resources already dedicated to their conservation, our work has focused primarily on the other four subfamilies in Hawaii, for which we estimate at least 40% of the known diversity may be extinct. Like the Amastridae, our recent survey work suggest that we have indeed lost a great deal of this once diverse family, but there also remains glimmers of hope. For example, we recently rediscovered a species, Auriculella pulchra, which many had thought extinct or at least extirpated from most of its range (Yeung et al. 2015). Similarly, we have found several cryptic species that await description (e.g. Figure 1J, Elasmias sp.) and a few species that seem to be locally abundant (e.g. Auriculella uniplicata Figure 2 in Puu Kukui Watershed, Maui, Hawaii).
Subfamilies (Hawaiian only): Achatinellinae, Auricullelinae, Pacificellinae, Tornatellidinae, and Tornatellininae
Number of recognized species: 209 – Achatinellinae (99), Auricullelinae (32), Pacificellinae (9), Tornatellidinae (66), and Tornatellininae (3)
Number of species found in recent surveys (including cryptic species): 75 - Achatinellinae (25), Auricullelinae (15), Pacificellinae (5), Tornatellidinae (30), and Tornatellininae (5)
Historical Distribution: Kauai, Oahu, Maui, Lanai, Molokai, Hawaii, Niihau, Kahoolawe, NWHI
Current Distribution: Kauai, Oahu, Maui, Lanai, Molokai, Hawaii, NWHI
Conservation Status: Most are likely endangered and the others are threatened
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Yeung, N.W. D. Chung, D.R. Sischo and K.A. Hayes. 2015. Rediscovery of Auriculella pulchra Pease, 1868 (Gastropoda: Pulmonata: Achatinellidae). Bishop Museum Occasional Papers 116:49-51.
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Figure 1: Representatives of the Hawaiian land snail families Amastridae (A-E; scale bar = 5 mm) and Achatinellidae (F-J; scale bar = 1mm). A) Amastra cylindrica, B) Laminella sanguinea, C) Tropidoptera rex, D) Carelia turricula, E) Leptachatina sp., F) Partulina porcellana, G) Auriculella crassula, H) Lamellidea cylindrica, I) Tornatellides sp., J) Elasmias sp. Scale bars = 5 mm (A-E).
Figure 2: Auriculella uniplicata gathered from a single location on Maui to show the high abundance of this species and the diversity of shell color patterns. More than 50 individuals of this species were counted from a 10x10 m area in less than 30 min.