Variations between winter and summer in the toxicity of copper to a population of the mysid Praunus flexuosus

Copper toxicity was tested on a coastal population of the mysid Praunus fle xuosus (Muller) from Southampton Water (Southern England) under winter and summer conditions. Ten-day toxicity tests were performed on the different l ife-cycle stages (female, male and juvenile) present in winter (December/Fe bruary) and summer (August). The individuals were in winter or summer physi ological condition and were exposed to seawater to which 0, 5, 25, 75 and 2 00 mug 1(-1) copper was added. There were significantly different copper to xicity effects in winter and summer. In winter mortality was less than or e qual to 1% at all levels of copper exposure, while in summer identical expo sure levels caused mortality of up to 93%. The 96 h LC50 was 30.8 mug 1(-1) copper added in the summer. In winter, the low mortality prevented calcula tion of LC50 There were differences in responses to copper between the life -cycle stages. Juveniles were more sensitive than adults, and were severely affected within 24 h. Females were more affected than males at lower doses and shorter exposure times.