It is estimated that there are over 500 million tonnes of Krill in the ocean, and that that biomass is the most for any multi-celled creature on the entire planet. They swim in dense swarms that can contain 10,000-30,000 individuals per square meter.
Unfortunately, Antarctic Krill numbers, and the numbers of other Krill species, have dropped nearly 80% since the 1970s. Increased Carbon Dioxide levels have already proven to be a huge detriment to the species. A continued downward trend could have drastic implications for the large marine animals that depend on them for food.