The aim of this thesis was to investigate the abilities of confamilial gammarid amphipods with differing latitudinal distribution patterns to compensate for environmental change and to examine the consequences. Interesting variations were observed in the strategies employed by gammarid amphipods to cope with environmental change. The boreal/temperate species, Gammarus duebeni, exhibits a high upper thermal tolerance and acclimatory ability, but at the cost of reduced growth and reproductive output. The warmer-water G. locustaappears to have a narrower tolerance and reduced ability to adjust to rapid temperature change, but at stable conditions within its thermal window and at higher salinities it is able to out-perform G. duebeni. G. duebenimay therefore be more likely to survive environmental change, but G. locustapopulations may be better able to recover from high mortality events. A similar upper thermal limit and temperature independence of metabolic was observed in the subarctic/boreal species G. oceanicuscompared with G. duebeni, however G. oceanicusalso demonstrated r-selected life history traits. G. oceanicusand G. locustaoccupy overlapping geographical ranges and the same low shore niche, but G. oceanicusappears to have a broader tolerance at a lower optimal temperature than G. locusta. Intraspecific variation was observed between two populations of G. duebenifrom Wales (53 °N) and Norway (70 °N). Following acclimation to common temperatures, the northern population was characterised by reduced upper thermal limits and rates of oxygen uptake, a greater thermal sensitivity of oxygen uptake, and evidence of the upregulation of protein synthesis and growth rates in the cold. The influence of the combined factors of salinity and temperature on physiological rate processes in G. duebeniwas complex. G. duebeniwas less able to adjust to rapid temperature change when acclimated to salinities equivalent to full strength seawater than when held in brackish conditions.