Angelfish must be kept in schools of six or more in at least an 80-gallon tank. They may show aggression toward other species ... keeping larger fish healthy. Gobies also eat algae.

Or have you noticed how the walls of a fish tank sometimes turn green and slimy ... while kelp is anchored to rocks on the ocean floor. Both of these types of algae feed and give shelter to other ...

A harmful algal bloom of Karenia mikimotoi made dozens of surfers sick and killed seadragons, fish and octopuses on two South Australian beaches.