The chemical compound chlorophyll allows phytoplankton to convert sunlight, carbon dioxide and minerals into edible carbohydrates and proteins. Small invertebrates such as krill and other fish larvae feed on these microscopic plants. This begins the food chain, where larger animals tend to depend on smaller ones for survival. The most abundant phytoplankton are called diatoms. There are up to 20,000 species of diatoms and, under favorable conditions, most can produce up to 100 million offspring a month. With such a large reproductive capacity, as many as a billion diatoms can be found in a single gallon of seawater. The phytoplankton that are not eaten by larger animals typically live only a couple of days. In addition, when water temperatures change drastically or there aren't enough nutrients, phytoplankton tend to die off quickly.
Coral is an oceanic plant that thrives in temperate conditions. It can grow up to four inches per year in ideal 73 F water. As coral grows, it builds on top of itself and expands outward. Stony coral colonies have an average lifespan of 5 to 10 years. Coral polyps (tiny organisms that create reef structures) have been known to live for centuries. The largest known coral structure in the world is the Great Barrier Reef, which lies off the coast of Queensland in Australia. This amazing structure stretches over 3000 kilometers (1800 miles) in length and can be seen from space. Coastal development and pollution are major human-induced threats to living coral.
Seagrasses are the only flowering plants that live underwater. They can be found in coastal regions around the world. Seagrasses stabilize ocean sediment and absorb nutrients from coastal river run-off. Seagrass meadows provide a safe habitat for many small marine animals. In doing this, they promote diverse and healthy populations. According to the Seagrass Watch organization in Australia, seagrass-algae beds are the third most valuable ecosystem in the world. The nutrient cycling services they provide are irreplaceable. Seagrasses have a high degree of plasticity and tend to thrive in large meadows. Human activity threatens seagrass growth in many coastal areas.
Kelp is a type of brown algae that grows in cold coastal waters. It grows fast and has been measured to reach 250 feet. Giant kelp is the largest oceanic plant on Earth and can live up to 7 years. Pollution and commercial harvesting threaten kelp populations. Kelp extracts are used in vitamins and cosmetics.
