Marine ecosystems are the largest of Earth's aquatic ecosystems and are distinguished by waters that have a high salt content. These systems contrast with freshwater ecosystems, which have a lower salt content.

Marine biodiversity and ecosystems. ... Healthy marine ecosystems are important for society since they provide services including food security, feed for livestock , raw materials for medicines, building materials from coral rock and sand, and natural defenses against hazards such as coastal erosion and inundation.There are various types of marine ecosystems, including salt marshes, estuaries, the ocean floor, the broad ocean, the inter-tidal zones, coral reefs, lagoons, and mangroves.