 Microscopic photosynthetic algae contribute a larger proportion of the world's photosynthetic output than all the terrestrial forests combined.Most of the niche occupied by sub plants on land is actually occupied by macroscopic algae in the ocean, such as "Sargassum" and kelp, which are commonly known as seaweeds that create kelp forests.Plants that survive in the sea are often found in shallow waters, such as the seagrasses (examples of which are eelgrass, "Zostera", and turtle grass, "Thalassia").