Ecophysiology of the common cockle (Cerastoderma edule L.) in Southampton Water with particular reference to pollution

Ecophysiological studies encompassing many aspects of population ecology and individual physiological functions on Cerastoderma edule have been carried out. Sites for study were carefully selected so as to include both areas in the proximity of a pollution source (i.e. Fawley, Tucker Pile, Bird Pile and Marchwood) and regions distant from overt polluting input (Dibden Bay, Netley and Woolston). In the sheltered central parts of the estuary longevity, abundance, growth rates and productivity were higher. In contrast most localities on the western side of the estuary showed reduced growth, abundance, longevity and productivity. The variation observed in the population parameters was attributed to pollution load (heavy metals and petroleum hydrocarbons) and other sediment properties (grain size and organic matter content) of sites. The results of seasonal, age and site to site variation in the concentrations of six heavy metals (copper, cadmium, lead, iron, nickel and zinc) in C.edule tissues and sediment indicate that the populations inhabiting areas in the proximity of the industrial complex are more contaminated than those outside the areas. The same trend was found for the total petroleum hydrocarbons of cockles and sediment; being highest at Fawley and Tucker Pile. Statistical analysis of data supported the idea that the variability in the concentrations of copper, zinc, petroleum hydrocarbons and sediment grain size bring about the differences observed in the population parameters. Based on the levels of these variables, four site groups were identified. The physiological impact of pollution on C.edule was studied in greater detail. The effect of the water-accommodated fraction of Fawley oil and copper concentrations was marked on the clearance rate and absorption efficiency. Cockles exposed to higher concentrations showed negative scope for growth after the second week of exposure. A highly significant inverse correlation was found between either the concentration of WAF or Cu and the scope for growth. The physiological conditions of C.edule in the field were also investigated. The measurements were carried out on the populations of cockles at Fawley (a polluted site) and Dibden Bay (a relatively uncontaminated site). The energy available for the growth of cockles inhabiting Dibden Bay was found to be ten times greater than that available to Fawley cockles. The body condition index measured for the cockles along Southampton Water throughout the year showed similar variance as that displayed for scope for growth. Finally, the results of the present study were discussed in relation to event in the natural habitat of cockles in Southampton Water.