Elizabeth Grossman

Nitrogen is absolutely crucial to life — an indispensable ingredient of DNA, proteins and essentially all living tissue — yet it also can choke the life out of aquatic ecosystems, destroy trees and sicken people when it shows up in excess at the wrong place, at the wrong time, in the wrong form.

Barely longer than your thumb, weighing under an ounce and nearly translucent, delicate crustaceans known as krill are vital to ocean ecosystems around the world.

The danger that the decline of bees and other pollinators represents to the world’s food supply was highlighted this week when the European Commission decided to ban a class of pesticides suspected of playing a role in so-called “colony collapse disorder.”

With contaminated water from Japan’s crippled Fukushima nuclear complex continuing to pour into the Pacific, scientists are concerned about how that radioactivity might affect marine life. Although the ocean’s capacity to dilute radiation is huge, signs are that nuclear isotopes are already moving up the local food chain.