Waves, tides and a gradient of exposure drive the structure and function of these productive intertidal ecosystems found mostly on high energy coasts. The biota includes filter feeders like barnacles, mussels and sea squirts which compete for limited space. Grazers like limpets and urchins consume small sessile algae, while predators such as crabs, fish and birds consume a wide range of prey. Organisms use microhabitats during low tide (e.g. rockpools, crevices) or have adaptations like shells to survive exposure to high temperatures, salinity and desiccation.