This underwater photo, taken off the coast of California, shows giant kelp whose air bladders help it float in the ocean. Kelp is just one example of the many types of algae, both macroscopic and microscopic, that play a crucial role in ocean ecosystems. On page 26 , Chuanmin Hu discusses the technologies that are helping scientists to better understand algae on a global scale and to make new discoveries in the field of ocean optics. (Photo by iStock.com/joebelanger.)