Studies on the growth and ecology of Helix asposa muller

• Main Author: Dan, N. A.
• Published: University of Manchester 1978
• Subjects: 594
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.551127

The snail Helix aspersa Müller on the Great Orme's Head Llandudno is usually found among rocks, hidden by layers of long thick grasses, or in the crevices of the rocks. They are usually found in groups both in winter and summer except during wet weather. The animals use some limestone boulders regularly as hibernacula, other boulders are used irregularly during winter, and some are used almost equally throughout the year. Juveniles of Helix aspersa grow very rapidly during late Spring and early Summer and. they grow fastest when their height is between 15 and 20 mm. Juveniles pass through one or two hibernation periods before reaching maturity. The population size varies considerably and is highest during late Spring and Summer. The highest number was during Summer 1976 when the area experienced long dry spells. This increase was due to immigration. The estimated survival rates for Helix aspersa were too low considering that some of them were known to survive for several years. This low estimate of survival rate was due principally to emigration. The animals' movements are maximum during Spring and Summer. There is no indication that Helix aspersa in the area showed any directed seasonal movement, but this species shows homing within a limited range. Helix aspersa at Llandudno and Birkdale consume a wide range of green plant materials. The major plants consumed are grasses and dicotyledonous leaves which are common in their habitat: some selection is shown in the choice of food. - The food plants are assimilated very efficiently by the snails, and their assimilation is both temperature and substrate dependent. Growth of Helix aspersa is influenced by temperature, light regime and calcium. The animals grow faster at higher temperatures and in alternating light and dark,. and. animals reared with excess of chalk grow faster and have heavier shells than those without. The activities of Helix aspersa, Cepaea nemoralis, Hy romia striolata and Candidula intersecta are temperature dependent. They show maximum activity between 13 and 22 C. Helix aspersa is the least active of the four species, Hygromia striolata the most active. In addition, Hygromia striolata shows activity at lower and higher temperatures than the other species. Cepaea nemoralis is more tolerant to low temperatures than Helix aspersa but less tolerant to-high temperatures. Increase in density has an influence on growth, mortality and food consumption. Interactions between snails might be responsible for slowing the growth rates in high density populations. The presence of mucus trails of other snails also inhibits activity but their effect seems to be short-lived. Space has an adverse influence on growth and mortality of the animals if it is provided below their requirements.