Practically at the opposite end of the size spectrum from tuna, which can attain gigantic proportions, billions of tiny krill -- small oceanic shrimp-like creatures -- serve as the foundation of food chains, especially in the southern oceans.
Forming stately forests that cover hundreds of unbroken miles of coastline in some areas, mangroves provide coastal societies with protection from extreme weather events and serve as nursery areas for many species, including fish that are important for both local food security and national revenues.
These single-celled, glass covered, free-floating (planktonic) organisms are the most abundant marine species on Earth and sustain the majority of the ocean's productivity. Without them serving as vast quantities of food for everything else, there would be few more complex life forms. Additionally, diatoms produce much of the oxygen we need.
Read the full post on Conservation International's blog, Human Nature.