Copepods (pods) are essentially required for any reef aquarium. They perform three important ecological tasks: (1) Graze on benthic microalgae, (2) scavenge detritus, and (3) serve as food for diverse zooplanktivores. They are so ubiquitous in nature, and even in captivity, that they commonly invade new tanks as hitchhikers on live rock, corals, etc.
While this hitchhiking is very much welcome by most hobbyists, it is not always followed by an establishment of residency. This is due to heavy predation by fish and corals. This predation too is welcome, as it is completely natural and copepods are a very, very nutritious food. However, it can make the process of establishing permanent populations (referred to as “seeding”) somewhat challenging in some situations.