Energy flux in a natural population of the land snail, Cepaea nemoralis L.

Energy flux in a population of Cepaea nemoralis L. living on a sand dune system was estimated in 1970 and 1971. Numbers and dynamics of the adults were studied by a capture-mark-recapture method, juveniles by quadrat sampling. Adult numbers were around a mean of 2.14 m-2 (mean annual biomass 14.7 kJ m-2 1970; 13.4 kJ m-2 1971).Eggs were laid in June, July and August and peak numbers of small juveniles (<6 mm) were present in October (20.7 m-2 1970; 7.8 m-2 1971). Mortality rates of the small animals was high and in the following season (1971) density of the next size class (6-11 mm) was much lower (4.9 m-2). Mean annual biomass of the whole population was 17.0 kJ m-2 in 1970 and 16.4 kJ m-2 in 1971. Growth rates were slow and variable. Adult production was calculated as the yield to carnivores and scavengers plus the continuous mucus production which was almost half the total. Juvenile production was calculated from quadrat sampling data. Total population production was 34.3 kJ m-2 in 1970 and 25.9 kJ m-2 in 1971.Adult respiration was measured in an open flow respirometer with gas analysis by gas chromatograph. Measurements were made in 1971 on field acclimated animals. Juvenile respiration measurements were made in Warburg respirometers. Population respiratory losses were 62.8 kJ m-2 and 41.8 kJ m-2 in the 2 years. In the calculation of population respiration, allowance was made for low metabolic rates during periods of aestivation and hibernation. Population activity was reduced by 90% after 5 days without rain. Population consumption, was estimated at 316.6 kJ m-2 and 239.0 kJ m-2 and assimilation efficiencies were from 30-40% on natural foods.Annual energy budgets were constructed and energy flux (P+R) was 97.0 kJ m-2 in 1970 and 77.6 kJ m-2 in 1971. The plot of log respiration against log production fell lower than that for most long-lived poikilotherms due to the inflation of the production estimate by mucus production.