In addition to typical marine environments, poecilostomatoid copepods may be found in such very particular habitats as anchialine caves and deep sea vents (both hydrothermal vents and cold seeps).
For certain environments, like hot springs or deep sea vents, the energy flux is sufficient to support this replacement activity to extremely high temperatures.
This finding comes from field observations at various vent sites around the world and laboratory experiments which reproduced the environment (temperature, pressure) found in the deep sea vents.