An organic carbon analysis of the growth of Potamopyrgus Jenkinsi (Smith) in relation to temperature and salinity

Abstract

Potamonyrgus jenkinsi (Smith) is a small gastropod living in freshwater and brackish habitats in Britain. It is currently extending its range in Europe. This study has involved the elucidation of the growth response of this mollusc to temperature and salinity, in the laboratory. Growth is maximised at 25°C and 14°/oo salinity. The method of growth analysis employed was based on the evaluation of the organic carbon content of individual P. jenkinsi. The growth rate results are presented in both shell length and carbon terms. The relations between carbon, dry weight and shell length were defined. Variations in these were found with growth conditions. The relation between carbon and shell length is : c = A 1m (1) This was employed in the linearised form : log c = m log 1 + a (where a = log A - eqn 1) The overall equation defined for P. jenkinsi under all conditions of salinity and temperature (pooled results) was : log c = 2.3078 log 1 + 1.0135 The relation of carbon to dry weight was of the form : c = n w + b This is a simple linear equation. (Terms used : c-organic carbon, 1-shell length, w-total dry wt., m,n,A,a and b - constants) The method of organic carbon analysis employed was a small scale development of that used by Russell Hunter et al (1968). In this form the method is ideal for evaluating the biomass of small individual invertebrates. The results in this work demonstrate the high degree of sensitivity and accuracy that can be achieved. Considerable differences in growth rate resulted from varying temperature and salinity. P. jenkinsi is both eurythermal and eurysaline. Temperature and salinity have been shown to interact synergistically in their effect on growth rates. The growth of P. jenkinsi is controlled with respect to salinity. No growth regulation was found in relation to temperature : growth rates conformed to the Arrhenius model. There appears to be some endogenous variation in growth potential with the time of year. The results are discussed in relation to current theories of biochemical and physiological adaptation to the physical and chemical aspects of the environment. Some consideration is given to the taxonomic state of P. jenkinsi. It is concluded that P. jenkinsi should remain as a single species unit. The species should not be subdivided as suggested by Warwick (1969).