2.4 DISCUSSION
The results of this study provide the first examination of copper, lead and zinc toxicity on E. chloroticus and H. iris larvae. All developmental anomalies recorded were severe and likely to result in larval death before settlement, for example the absence of shell in H. iris. In the case of delayed or arrested development,development might resume when larvae return to uncontaminated water. A recent study showed that sea urchin larvae (Strongylocentrotus nudus from Korea)displaying arrested development after exposure to triclosan could recover only if exposure was for less than 30 h (Hwang et al. 2014). Further, prolonging time in the plankton due to increased development time can have a range of adverse effects, such as increased predation risk, dispersal away from suitable habitat, and lower settlement success and juvenile growth rate, especially for non-feeding larvae such as H. iris that are dependent on maternal reserves (Pechenik 1999). Therefore, although toxic effects observed are sublethal in the sense that they are categorized as developmental abnormalities, they are likely to result in mortality, in many cases quite rapidly.