section_path: Features/Coasts and islands
section_name: Coasts and islands
paragraph_text: Coasts and islands
  
  The shoreline is the interface between the land and the ocean. It migrates each day as tides rise and fall, and moves over long periods of time as sea levels change. The shore extends from the low tide line to the highest elevation that can be reached by storm waves, and the coast stretches out inland until the point where ocean-related features are no longer found.
  
  When land is in contact with bodies of water, the land is likely weathered and eroded. The weathering of a coastline may be impacted by the tides, caused by changes in gravitational forces on larger bodies of water. The precise length of Earth's coastline is indeterminable due to the coastline paradox. According to The World Factbook, the coastline is around 356,000 kilometres (221,000 mi), while according to the World Resources Institute, it is 1,634,701 kilometres (1,015,756 mi).
  
  Coasts are important zones in natural ecosystems, often home to a wide range of biodiversity. On land, they harbour important ecosystems such as freshwater or estuarine wetlands, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor saltmarshes, mangroves or seagrasses, all of which can provide nursery habitat for finfish, shellfish, and other aquatic species. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g. mussels, starfish, barnacles) and various kinds of seaweeds. Along tropical coasts with clear, nutrient-poor water, coral reefs can often be found between depths of 1–50 meters (3.3–164.0 feet).
  
  According to a United Nations atlas, 44% of all people live within 150 km (93 mi) of the sea. Because of their importance in society and high concentration of population, the coast is important for major parts of the global food and economic system, and they provide many ecosystem services to humankind. For example, important human activities happen in port cities. Coastal fisheries (commercial, recreational, and subsistence) and aquaculture are major economic activities and create jobs, livelihoods, and protein for the majority of coastal human populations. Other coastal spaces like beaches and seaside resorts generate large revenues through tourism. Marine coastal ecosystems can also provide protection against sea level rise and tsunamis. In many countries, mangroves are the primary source of wood for fuel (e.g. charcoal) and building material. Coastal ecosystems like mangroves and seagrasses have a much higher capacity for carbon sequestration than many terrestrial ecosystems, and as such can play a critical role in the near future to help mitigate climate change effects by uptake of atmospheric anthropogenic carbon dioxide.
  
  An isolated land habitat surrounded by water is an island, while a chain of islands is an archipelago. The smaller the island, the larger the percentage of its land area will be adjacent to the water, and subsequently will be coast or beach. Islands can be formed by a variety of processes. The Hawaiian islands, for example, even though they are not near a plate boundary, formed from isolated volcanic activity. Atolls are ring-shaped islands made of coral, created when subsidence causes an island to sink beneath the ocean surface and leaves a ring of reefs around it.