Marine ecosystems are essential for the overall health of both marine and terrestrial environments. According to the World Resource Center, coastal habitats account for about one-third of marine biological productivity. Estuarine ecosystems, such as salt marshes, seagrass meadows and mangrove forests, are among the most productive ecosystems on the planet. Coral reefs provide food and shelter to the highest levels of marine diversity in the world.
Marine ecosystems usually have a large biodiversity and are therefore thought to have a good resistance against invasive species. However, exceptions have been observed, and the mechanisms responsible in determining the success of an invasion are not yet clear.
According to NOAA, salt marshes are defined as "coastal wetlands that are flooded and drained by salt water brought in by the tides". These marshy grounds are able to prevent flooding as well as help maintain water quality by absorbing rainwater and runoff that comes through the area.
Intertidal zones are the areas that are visible during low tide and covered up by saltwater during high tide. In these zones simple organisms can be found in tide pools. These areas also have a higher salinity because salt is left poration has occurred.
Estuaries occur where there is a noticeable change in salinity between saltwater and freshwater sources, for example, the confluence between a river and an ocean. Many organisms rely on this fragile ecosystem at least once during their life cycle.