Caroline Naylor

Scope for growth in Gammarus pulex, a freshwater benthic detritivore

Although toxic substances affect the physiological processes of individual organisms, their ecological impacts occur at the population and community levels. However, physiological processes can often be assessed more easily and precisely than population and community ones. Here we argue that ‘scope for growth’, the difference between the energy input to an organism from its food and the output from respiratory metabolism, can give a good physiological measure of stress that, at least in principle, is straightforwardly related to population and community processes. We describe, in detail, how ‘scope for growth’ can be measured in Gammarus pulex (Crustacea, Amphipoda). The results indicate that both zinc and low pH can significantly reduce the scope for growth of individuals and that the most sensitive component of the energy budget is food absorption.

Effect of Stress on a Freshwater Benthic Detritivore: Scope for Growth in Gammarus pulex

Scope for growth (SfG), a measure of energy balance (between food intake and metabolic output) within animals, has been used as an indicator of pollution stress in marine systems. However, it has not been used commonly in freshwater systems and here we investigate the sensitivity of SfG in Gammarus pulex, a benthic freshwater crustacean, under conditions often associated with pollution. The effects of four specific substances were investigated; a metal (zinc), an organic (3,4-dichloroaniline), and two dissolved gases (oxygen and ammonia). In all cases SfG was reduced by the stress, primarily due to a depression in energy intake. Only with ammonia was energy output (respiration) significantly affected.

Field deployment of a scope for growth assay involving Gammarus pulex, a freshwater benthic invertebrate

Scope for growth (SfG) is a measure of the energy balance of an animal (i.e., the difference between energy intake and metabolic output). The SfG of marine invertebrates, particularly the mussel Mytilus edulis, has been successfully used as the basis of a field bioassay to detect a range of stresses both natural (temperature, food, salinity) and anthropogenic (hydrocarbons, sewage sludge). SfG of the freshwater amphipod Gammarus pulex was found to be a sensitive indicator of stress under laboratory conditions and here we describe the field deployment of this technique and present data from three field trials. In every case, SfG was reduced at the downstream polluted site compared with that at an upstream reference site. This reduction in SfG was the result of a decrease in energy intake (absorption) rather than an increase in energy expenditure (respiration).

Induction of cadmium tolerance in two clones of Daphnia magna straus

1. The abilities of two different genotypes of Daphnia magna to develop cadmium resistance through physiological adaptation, after pre-exposure to sublethal concentrations of Cd, Zn and Cd/Zn mixtures, was investigated. 2. The induced elevation in cadmium tolerance was shown to be associated with an increase in the body concentration of metallothionein-like proteins. 3. The highly significant difference in acute responses to cadmium between the two clones reduced after pre-exposure. 4. Differences in cadmium tolerance were shown to be associated with differences in cadmium uptake.

Effect of differing maternal food ration on susceptibility of Daphnia magna Straus neonates to toxic substances

Abstract Maternal stocking density and hence available ration affects both length and dry weight of neonates. As ration per adult Daphnia increased the size of neonates decreased. There was some suggestion that neonate size had an effect on their susceptibility to some toxicants. The results here are not decisive, but are sufficiently indicative to counsel caution in the culture of mothers when generating reonates for tests and to suggest that further research is needed to determine the relationship between size and sensitivity.

Effect of differing maternal ration on adult fecundity and offspring size in laboratory cultures of Daphnia magna Straus for ecotoxicological testing

Abstract By manipulating maternal ration both numbers and lengths of D. magna neonates could be modified. Maternal ration was adjusted by maintaining a constant volume of medium and added food (Chlorella), but varying the number of daphnids per vessel. At low stocking densities, larger numbers of smaller neonates were produced per female than at higher stocking densities, in which fewer, larger neonates were produced per female. The results indicate that careful control of maternal ration is necessary to maintain a predictable supply of uniform neonates for ecotoxicological purposes.

Frozen algae as food for Daphnia magna straus in toxicity testing

As EC validity criteria for the production of Daphnia magna neonates in standard toxicity tests set fecundity minima which must be attained, it is important that culture conditions provide an adequate ration of high quality food. Maintaining a steady supply of fresh algae can be problematical so the possibility of using frozen food was investigated. The performance of three generations of D. magna fed on diets of fresh or frozen Chlorella was compared. There were no significant effects on fecundity due to food type or generation. Cumulative fecundity (over 21 days) on fresh or frozen food exceeded 120 neonates per female and satisfied that EC validity criterion (60 neonates per female). In addition criteria relating to survival and variability were met. We conclude that frozen Chlorella are an acceptable substitute for fresh algae.