Surprisingly however, young juveniles were more vulnerable than larvae to a first copper exposure. Indeed, a short pulse of the highest concentration copper to naive juveniles impaired radial growth, while no direct effect of copper on larval size or survival was observed. Copper toxicity has never been assessed for young juvenile urchins. Comparison of sensitivity to stressors between life stages of the sea urchin usually includes all the stages of larval development until, or shortly after,metamorphosis, but not young settlers and juveniles (Kobayashi 1980, King & Riddle 2001).
These findings confirm that E. chloroticus is sensitive to copper during the whole larval stage as well as shortly after settlement, although severity of impact decreases with larval age. Therefore, punctuated pollution events such as runoff are likely to affect, to some extent, all larval and young juvenile cohorts that occur in locations where they are common, such as near river mouths or in harbours.
Besides exposure to copper, various larval traits significantly impacted subsequent performance in settlers and juveniles. Rudiment size at the end of the larval stage seems to be the best predictor of settler performance, significantly influencing settlement success, body size at settlement, settler survival and growth. This suggests that stress affecting rudiment formation may have long lasting impacts on settler performance. Larval body size at the end of the larval stage also influenced spine size at settlement and settler growth. This provides further evidence that ‘metamorphosis is not a new beginning’ (Pechenik et al. 1998) and that larval traits have a continued influence on performance in later life stages.