When we think of plants, we usually think of those whose roots are firmly planted in the ground. However, there are a whole group of plants who have no roots and, in fact, don't even need soil. Some don't even need anything solid in which to take root in and to thrive. Without these plants--many of which are invisible to the naked eye--life in our tropical oceans would be much different.
Red algae can be found in almost any area of the tropical oceans. While sometimes the algae attaches itself to something else, it can also be found growing and thriving free-floating in the ocean currents.
One of the oldest plants known (it is estimated to be approximately 2 billion years old), red algae is in part responsible for another well-known feature of the tropical ocean--the coral reef. The coral, which are living animals, feed off the red algae that attaches itself to them. As the coral reefs grow, they in turn become home to a number of different species of fish, which also feed off the red algae.
Red algae is unique in its location; the red pigment contained in the algae makes it more efficient in absorbing light, and can consequently be found in much deeper waters than blue or green algae.
Dinoflagellates is the name for a family of unique, single-celled plant organisms. They're considered plants because they make their own food from the sunlight they absorb, and are among the primary producers found in tropical oceans.
At certain times of the year when the tide changes, an upswelling of waters brings fresh nutrients up to the surface from the bottom of the ocean. This causes a massive population boom in the dinoflagellates, and it's this increase in reproduction that causes red tides like those frequently seen in areas like the Gulf of Mexico. Red tides frequently occur in the late summer months, and can be deadly to marine life susceptible to the neurotoxins that dinoflagellates produce.
Like red algae, dinoflagellates also play an important role in the formation of coral reefs. The coral consumes the dinoflagellates, which are then absorbed into the tissues of the coral. This is done without actually harming the dinoflagellates, which then go on to produce carbohydrates inside the coral. Coral that has this boost of nutrients forms reefs much quicker than coral that does not have dinoflagellates present.
Coralline algae is a relative of red algae. However, coralline algae is a calcified version of red algae; it has begun to produce calcium in its cell walls after adhering to coral.
These plants are both flexible and hard; the structures themselves are calcified to form a hard skeleton, but they do have calcium-free sections that allow the plant to bend and flex much like human joints do. They are adapted to live in tropical, coastal areas in waters up to 100 feet deep.
In some areas, such as the Mediterranean Sea, coralline algae provides the majority of the inner building blocks of the coral reefs. Because of this, they not only form a symbiotic relationship with the coral organisms, but are also responsible for helping to create a living environment for countless species of marine life.