There are two overall types of tropical ocean plants. One type is plankton. The other types are seaweeds. Plants growing in tropical oceans serve important roles in the oceanic food chain. Many fish and marine mammals live on plankton. Others consume seaweed. Seaweed is also a part of the diet in many cultures that live along the ocean, especially in Asia.
There are two general classes of plankton. One class of plankton is actually animal plankton. Plant-type plankton is called phytoplankton. Phytoplankton in tropical ocean waters is responsible for the green component in greenish-blue waters. Phytoplankton serves as the fundamental building block of the oceanic food chain. Animals as small as zooplankton, or animal plankton, feed on phytoplankton. On the other end of the scale, animals as large as whales feed on a combined diet of zooplankton and phytoplankton.
Although kelp is often associated with temperate oceans, and some species of kelp are adapted to tropical oceans. Kelp are very long seaweed that grow in "forests" in cooler waters. In the tropics, however, they do not grow as densely. Although it can sometimes grow near the surface, kelp usually grows at between 40 and 200 feet below the surface of the ocean.
Caulerpa is attractive tropical seaweed that is popular in home saltwater aquariums. Caulerpa has a fine feather-like pattern and grows very well in artificial aquarium conditions. However, this ability to withstand and survive adverse conditions makes this seaweed invasive in many ocean environments. As aquarium owners dumped seaweed in the warm oceans of southern California, caulerpa quickly became established at the expense of native seaweeds.
Ecklonia radiate is a type of tropical seaweed that grows in kelp forests at between 30 and 80 feet deep. This seaweed is a food source for fish and marine animals and is harvested, in some places, as a human food source as well.
Padina boergesenii is a sea grass that lives on sand dunes around tropical ocean islands and atolls. The biomass of this type of seaweed is a major contributor to the food sources for marine fish, reptiles, and other animals. Padina boergensenii is a perennial ocean plant that tends to be most common during pre-monsoon seasons.