Morro Shoulderband Snail
Morro Shoulderband Snail
|Listed||December 15, 1994|
|Description||Slightly translucent snail which has five to six whorls and a globose shell.|
|Habitat||Coastal dune and scrub communities.|
|Food||Probably the fungal mycelia (webs or mats of non-reproductive fungal strands) growing on decaying plant litter.|
|Threats||Development, invasion of non-native plant species, senescence of dune vegetation, heavy off-highway use of recreational vehicles.|
The shell of the Morro shoulderband snail (Helminthoglypta walkeriana ), also commonly known as the banded dune snail, is slightly translucent and has five to six whorls. Its dimensions are 0.7-1.1 in (1.8-2.8 cm) in diameter and 0.6-1.0 in (1.5-2.5 cm) in height. The Morro shoulderband snail can be distinguished from another native snail in the same area, the Big Sur shoulderband snail (H. urnbilicata ), by its more globose shell shape and presence of incised spiral grooves. The shell of the Big Sur shoulderband snail tends to be flatter and shinier. The brown garden snail (Helix aspersa ) also occurs in Los Osos with the Morro shoulderband snail and has a marbled pattern on its shell, whereas the Morro shoulderband snail has one narrow dark brown spiral band on the shoulder. The Morro shoulder-band's spire is low-domed, and half or more of the umbilicus (the cavity in the center of the base of a spiral shell that is surrounded by the whorls) is covered by the apertural lip.
The Morro shoulderband snail. probably feeds on the fungal mycelia (webs or mats of nonreproductive fungal strands) growing on decaying plant litter. The Morro shoulderband snail, belonging in the native snail fauna of California, is not a garden pest and is essentially harmless to gardens. Sarcophagid flies have been observed to parasitize the Morro shoulderband snail. Empty puparia ("cases" left behind by adults emerging from pupae) were observed in empty snail shells. Mortality from infestations of larvae of this parasitoid fly often occurs before the snails reach reproductive maturity. The flies may have a significant impact on the population of the snail. Seasonal drought and/or heat may contribute to the snail's egg mortality. Based on shell examination, it appears that rodents may prey on the snail.
The Morro shoulderband snail occurs in coastal dune and scrub communities. Through most of its range, the dominant shrub associated with the snail's habitat is mock heather. Other prominent shrub and succulent species are buckwheat (Fagopyrum sp.), eriastrum (Eriastrum sp.), chamisso lupine (Lupinus chamissonis ), dudleya (Dudleya sp.), and in more inland locations, California sagebrush (Artemis californica ) and black sage (Salvia melliflora ). The Morro shoulderband snail has also been found under mats of non-native fig-marigold.
Away from the immediate coast, immature scrub in earlier successional stages may offer more favorable shelter sites than mature senescent stands of coastal dune scrub. The immature shrubs provide canopy shelter for the snail, whereas the lower limbs of larger older shrubs may be too far off the ground to offer good shelter. In addition, mature stands produce twiggy litter low in food value.
The Morro shoulderband snail is found only in western San Luis Obispo County. At the time of listing, the Morro shoulderband snail was known to be distributed near Morro Bay. Its currently known range includes areas south of Morro Bay, west of Los Osos Creek and north of Hazard Canyon. Historically, the species has also been reported near the city of San Luis Obispo and south of Cayucos.
The Morro shoulderband snail is threatened by destruction of its habitat due to increasing development and by degradation of its habitat due to invasion of non-native plant species, especially veldt grass, structural changes to its habitat due to senescence of dune vegetation, and recreational use of heavy off-highway activity.
The Morro shoulderband snail may be experiencing competition from the brown garden snail (Helix aspersa ). The brown garden snail, presumed to be an escapee from an adjacent golf course and housing development, has established feral populations on the spit of Morro Bay. While estivation sites and food preferences for the two snails differ, competition for shelter sites may limit the numbers of Morro shoulderband snails. The coastal dune scrub community within the survey area is mature to the point that lower limbs of the large older shrubs may be too far off the ground to offer good shelter. Both snails occasionally use the alien M. chilense, as well as pieces of particleboard for shelter sites. Increasing development surrounding the State Parks will increase threats from this and other exotic animals and plants that disperse from developed areas.
At least several Morro shoulderband snails have been killed as a result of controlled burning of coastal scrub that was carried out to improve habitat for the endangered Morro Bay kangaroo rat within Montana de Oro State Park. Park staff are aware of the presence of the snails, have conducted pre-burn searches for them, but have not detected any in the areas that have been burned since Roth's first reported fire-induced mortalities. Drought and/or heat may have contributed to egg mortality in the Morro shoulderband snail. Other snail taxa that occur within California's areas of Mediterranean climate copulate, oviposit, and undergo an active growth phase during the rainy season. Intact but desiccated Helminthoglypta eggs were found in 1985 scattered in considerable numbers within the survey area, though the species could not be determined. It was suggested that this represented several years' accumulation of egg deposits whose viability may have been lowered by drought and/or heat conditions.
The use of snail baits and non-native predatory snails to control the brown garden snail could cause mortality to the Morro shoulderband snail. Non-native predatory snails have been observed preying on other native California snails. The importation and transportation of non-native snails are prohibited in San Luis Obispo County by the California Department of Fish and Game.
Conservation and Recovery
Several habitat conservation plans are being developed to allow for the incidental take of the Morro shoulderband snail during the development of small subdivisions and single family residences. Such actions would result in the loss of habitat for the Morro shoulderband snail, but contiguous blocks of remaining habitat will likely be preserved and managed in perpetuity.
A sewer treatment facility is currently proposed for Los Osos. Construction of this facility will destroy habitat for the Morro shoulderband snail, while operation of the facility will indirectly cause destruction of habitat by allowing the lifting of a moratorium on development. The County of San Luis Obispo will acquire habitat to mitigate for the direct and indirect effects of the sewer treatment facility.
U.S. Fish and Wildlife Service is funding surveys and habitat research on the Morro shoulderband snail on state park lands. A veldt grass control project for snail habitat on state park lands began in 1998.
U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
U.S. Fish and Wildlife Service. 1998. "Recovery Plan for Morro Shoulderband Snail and Four Plants from Western San Luis Obispo County, California." U.S. Fish and Wildlife Service, Portland, Oregon. 75 pp.