Plankton are tiny. With the exception of critters like jellyfish and cephalopods, which are technically "megaplankton," most plankton are smaller than 2 millimeters long. Phytoplankton, the plants of the plankton world, are microscopic.
But when plankton hang out in large aggregations, you can see it from space. The mind reels at the notion that those swirls of light blue are made up of so many tiny little organisms that you could start counting them and never stop.
The image above was taken on May 30 by the "Moderate Resolution Imaging Spectroradiometer" (MODIS) on NASA's Terra satellite. Phytoplankton "blooms," like the one seen in this photo in the North Sea, occur when phytoplankton come upon a nutrient bounty, allowing them to eat and reproduce like... well, like plankton. The usual bunny metaphor just doesn't seem sufficient here.