In this UNESCO video on YouTube hear Peter Thomson explain the 4th principle, link. He is the United Nations Secretary-General's Special Envoy for the Ocean, which means he works with different countries as a diplomat and encourages them to chose best practices for the sustainability and future of the ocean. He is from Fiji, an island in the Pacific Ocean and in his career played an important role in the creation of Sustainable Development Goal 14, which focuses on the ocean.

The Academy of Natural Science at Drexel University has a beautiful webpage story about diatoms, on the "Google Arts & Culture" platform. Beautiful microscope images and descriptions share a small piece of their huge "Diatom Herbarium" collection (one of the two largest collections in the world), link.

Show how to look at diatoms from pond water or sea water under a microscope in class 

Diatoms are tiny, single-celled organisms. They use sunlight to make their own food, like plants do, but they belong to a different group of organisms called algae. Each species has a unique, transparent shell made of silica, the same substance found in glass. They drift in the surface waters of the ocean as phytoplankton and produce energy through photosynthesis. Scientist study the population of diatoms because they are an indicator of water quality and are the basis of the marine food web. As this book is about raising awareness about our ocean, diatoms are the perfect "main character" to point out activities to do to become more sensitive to the environment.