Seaweeds primarily live in saltwater environments, including oceans and seas, where they form the base of many food chains and provide habitat. While some green seaweeds can be found in freshwater or estuarine environments, the majority of brown and red seaweeds are strictly marine.

Barnacles are exclusively marine crustaceans, related to crabs and lobsters. They are commonly found attached to hard surfaces like rocks, piers, and boat hulls in shallow and tidal (intertidal) waters within marine habitats. Both organisms are characteristic of rocky shores within marine ecosystems.