Hydrozoans are found in nearly all marine habitats, except perhaps heavy surf zones. They are most abundant and diverse in warm shallow waters, probably as a reflection of food abundance. The small number of freshwater species occur in both lotic and lentic habitats, and are more abundant in eutrophic and mesotrophic waters.
Habitat Regions: temperate ; tropical ; polar ; saltwater or marine ; freshwater
Aquatic Biomes: pelagic ; benthic ; reef ; oceanic vent ; lakes and ponds; rivers and streams; temporary pools; coastal ; abyssal ; brackish water
Wetlands: marsh ; swamp
Other Habitat Features: estuarine ; intertidal or littoral