Ultraviolet B radiation impairs coral reef fish development.

Loss of structural habitat complexity associated with habitat degradation in marine systems may expose early life stages of fishes to harsh environmental conditions. Specifically, loss of coral cover means less suitable refuge is available for some reef fish species to lay their eggs, exposing them to pervasive stressors such as ultraviolet radiation (UVR). Here, using laboratory experiments, we exposed embryos of the clownfish Amphiprion ocellaris for 2 h daily to two UVR levels reflective of their depth at settlement; high UVR (280 µW m-2), reflective of shallow depths, and low UVR (80 µW m-2), reflective of deeper depths over their embryonic period, and then measured changes in mass, yolk sac volume, DNA damage, and survival. Despite being exposed to ecologically relevant levels of UV radiation, there was 100% mortality before hatching and inflated yolk sacs in both high and low UVR-treated animals. Exposure to UVR also resulted in DNA damage, albeit only in high UVR treatments. It is evident from our results that the protection that the reef can offer from UVR is critical for the survival of clownfish. Our results also underscore the need for future work to consider this often-neglected stressor and the role of adequate refuge for the healthy development of early-life stages of reef organisms.