Shell decomposition rates in relation to shell size and habitat conditions in contrasting types of Central European forests
Abstract
Empty mollusc shells provide evidence of the species' presence over various temporal and spatial scales. However, the persistence of the shell can differ depending on the levels of soil pH and soil humidity.
Although this is generally known, there are virtually no experimental data on shell decomposition rate and its relation to shell size and site conditions. Here we study disappearance and degradation rates of shells of nine common species covering the variation in shell size and ecological requirements of temperate European land snails.
These shells were exposed to decomposition during a 3-year field experiment in six forest types, representing a gradient of soil pH and humidity. Rates of disappearance and (in larger species) of degradation were estimated by removing the exposed shells and measuring their condition after 6, 12, 24 and 36 months.
The disappearance rate was modelled by generalized linear models in relation to species and forest type. The data showed an increase in shell disappearance rate from dry alkaline through to wet acidic forests, but the effect of species size outweighed that of habitat.
While shells of large species only started to disappear after 3 years in wet acidic sites, most shells of small species had already disappeared by that time. In contrast, in dry habitats the loss of small shells only started after 3 years.
The results clearly support the benefits of using empty shells in mollusc research, especially less damaged shells, which represent the individuals that were alive less than 2 years ago, regardless of shell size and habitat type. However, the marked differences in decomposition rate related to shell size and habitat also highlight the need to take these into account if a studied parameter is confounded with variation in shell size and/or site alkalinity or humidity.