What Type of Plants Grow in Salt Water?

Marine plant life is the basis for all ocean life. Most marine plants are located along the coastal zones or, if they are in open water, in the eutrophic zone, the upper surface water of the ocean where sunlight can penetrate. Like all plants, marine plants require sunlight for photosynthesis. Plants that thrive in saltwater have special salt excreting cells or a gelatinous coating that protects them from becoming saturated with salt water.

An aerial view of ocean plants.

Phytoplankton

Phytoplankton is the single most important form of marine plant life. They are small, often microscopic, and have a lifespan of only one to two days. Phytoplankton thrives in all the oceans of the world, floating on the surface of the water or just below. Phytoplankton requires nutrients, such as iron, that seep up from the colder, deeper ocean waters. When the waters are too warm, as during an El Nino, the plankton die faster, compromising ocean life. When they die, they sink to the bottom, where their remains collectively make up the largest storage of carbon dioxide in the world. In addition to phytoplankton, there are also nanoplakton and zooplankton.

Kelp

Kelp is a form of brown algae that grows in aptly called kelp forests worldwide. Kelp lives along coastal areas and in the eutrophic ocean zone, usually never exceeding depths of 15 to 40 meters and never in water warmer than 68 degrees. Kelp plants do not have roots, but rather holdfasts, root-like structures that allow the plant to adhere to rocks or other oceanic structures for stability. Kelp has bubbles growing along the stems called gas bladders to hold them upright.

Rockweed

Rockweed is a different type of brown algae that grows along coastal areas. The physical structure of rockweed varies with location and salinity, being larger in saltier, calmer waters. Rockweed is a source of food and a hiding place for small invertebrates and fish like pollock. Rockweed sustains life on the bottom of the food web.

Seagrass

Seagrasses are angiosperms, or flowering plants, that closely resemble terrestrial grasses. They grow in underwater meadows, often near shorelines along muddy or sandy bottoms. Seagrasses vary in size from the size of a fingernail to 7 meters tall. Seagrass meadows can include many species of seagrass, or be limited to only one. Seagrass provides food for animals such as sea urchins and crabs and provides protection from predation for small life forms.

Mangrove Trees

Mangrove trees grow near salt water where soil may be rich or poor in oxygen; they are commonly found in estuaries. Mangrove trees can grow aerial roots, allowing the tree to breathe oxygen from the air if the soil is depleted. Mangrove trees expel some salt at their roots but can tolerate salt in their tissues at a ratio of one-tenth the salinity of seawater. Excess salt is stored in leaves, where it is removed via specialized cells, or the leaves are shed altogether.

References

• Lenntech: Water Ecology FAQ
• NASA: What are Phytoplankton?
• Office of Naval Research: Kelp Characteristics

Resources

• Kelp Forests
• ScienceDaily: Satellite Detects Red Glow to Map Global Ocean Plant Health