His mission has gradually evolved, from underwater photographer to advocate, as his pioneering new techniques bring the world ever closer to the issues the oceans face.

主句：His mission has gradually evolved, from underwater photographer to advocate，介词短语from underwater......作状语。

时间状语从句：as his pioneering new techniques bring the world ever closer to the issues the oceans face，as在这里可以理解为随着......。

the issues the oceans face：海洋面临的问题，the oceans face是省略that的定语从句，修饰先行词issues。

该句大意：（随着）他创新性的技术让世界对于海洋面临的问题有了更为深入的了解，他的使命也（由此）从海底摄影师逐渐演变为倡导者。