In this lecture we will discuss what plankton are and what they do, and discuss some aspects of food webs.
Most plankton are either slow-swimming or so small that their swimming speed is small.
Diatoms grow by division with the frustule getting ever smaller, after which they go through a sexual stage that grows without a frustule. Diatoms often appear yellow-brown, and can color the water noticeably. These are mostly considered nutritious food for zooplankton. Diatom frustules are the major ingredient of diatomaceous earth, and are a significant source of siliceous sediments at high latitudes. Diatoms are also the source of much of the world's petroleum deposits.