Chapter 15 Wetlands 367 Copyright Goodheart-Willcox Co., Inc. Nearly 70% of the coral reefs in the world are in Southern Asia and the Pacifi c Ocean. The largest coral reef system is the Great Bar- rier Reef off the Australian coast, Figure 15-10. The third largest reef system in the world is the Great Florida Reef, which extends from the Atlantic coast to the Dry Tortugas in the Gulf of Mexico. The United States also has coral reefs off the coast of Texas, Puerto Rico, the US Virgin Islands, and Hawaii. Coral reef wetlands may also be referred to as marine wetlands. Saltwater Marshes Saltwater marshes or tidal saltwater marshes are coastal wetlands that are regularly fl ooded by the ocean’s tides, Figure 15-11. The incoming tides constantly bring in sediments, nutrients, and a steady water supply. Saltwater marshes occur in low-lying areas along the coast and in estuary locations. An estuary is the lower end of a river where the river meets the sea. Saltwater marshes provide protection against soil erosion and inland fl ooding and habitat for many species of wildlife, such as migratory birds. Migratory birds raise their young in salt marshes because of the abundant food source and the tall grasses that provide protection from predators. Many marine fi sh also use saltwater marshes as nursery grounds. Saltwater marshes can be found on all coasts of the United States, but they are most common along the coast in the Gulf of Mexico. These marshes supply breeding grounds for many species that support the fi shing industry. Shrimp, crabs, mussels, and crawfi sh are important cash-crop aquatic species that use the calm water as a breeding ground. Tanya Puntti/Shutterstock.com Figure 15-10. The Great Barrier Reef off the coast of Australia covers over 133,000 square miles of ocean and is the largest living organism on Earth’s surface. Has the Great Barrier Reef suffered from global climate change? JuneJ/Shutterstock.com Figure 15-11. Mussels are commonly left behind with tidal flows. The mussels can often be harvested as a cash crop, and those that are not collected may become a tasty treat for migratory birds.