Chemical process by which phytoplankton and harmful algal blooms grown

Phytoplankton, including harmful algae, need the right combination of ingredients to grow. They need sunlight, which is bright near the surface but gets dimmer with depth. They need nutrients, such as nitrogen, phosphorus, and silica, which are plentiful in dark, deep waters but scarce near the surface. One example of a sweet spot for peak growth occurs a few meters below the surface, where phytoplankton have enough of both nutrients and sunlight. (Illustration by Natalie Renier, © Woods Hole Oceanographic Institution)