Pioneer species are hardy species which are the first to colonize previously disrupted or damaged ecosystems, beginning a chain of ecological succession that ultimately leads to a more biodiverse steady-state ecosystem. For example:
Barren sand - Lyme grass, Sea couch grass, Marram grass
Salt water - green algae, Marine eel grass, Pickleweed, and Cordgrass
Clear water - algae, mosses, Freshwater eel grass