Gastrulation is a critical point in the development of an embryo. Damage to embryos prior to gastrulation via UVR effects on cytokinesis or DNA will have a dramatic negative effect on embryo survival. Once embryos exposed to UVR complete gastrulation, there may be delays in the development program and mortality associated with incomplete or abnormal metamorphosis to larvae. One way to assess these ... effects is a coordinated set of measurements on the timing of cytokinesis and DNA damage, measured as cyclobutane pyrimidine dimer formation (CPD). Plankton samples were collected from the water surface to at least 15m depth with the distribution and abundance of the sea urchin Sterechinus neumayeri embryos and larvae under the annual sea ice assessed. The embryos and larvae were then used to compare the rates of UVR induced DNA damage with depth and ambient UVB irradiance levels. Five day in situ UVR exposures were made at three exposure depths (0.5, 1.5 and 5m) and three UV treatments (UV-B-, ambient UV-R- and Full UV) on three development stages (freshly fertilised eggs, early embryos blastula/gastrula and 4-armed pluteus larvae). The eggs of the nemertean worm Parbolarsia were also exposed and analysed. A second experiment was conducted where the period of exposure was extended to assess the effects of UVR over a longer period of larval development. During this time, embryos were exposed to one of two UVR treatments at 2 depths below the sea ice (0.5 and 5m) and were sampled at four times after outplanting. A third experiment involved in vitro experiments using 4 early development stages including freshly fertilised eggs, gastrula, freshly hatched blastula and 4 armed plutei were exposed to 295, 305, 320, 335, 345, 360, 375 and 400nm UVR wavelengths. Quantification of cytokinesis and cyclobutane pyrimidine dimer formation were analysed in New Zealand. Experiments were conducted over a number of seasons to build up an understanding on the relationship between in situ UV-B and damage to larvae under varying column ozone concentrations (the ozone hole is different every year).