(LJF image)Ī fringing reef forms along the shoreline of most new tropical islands. Over time a thriving community will be found on land as well as in the ocean.įringing reef showing island and reef growing right next to the island. These forms may stay and establish themselves if conditions there are good for them. If there is no more volcanic activity and the island cools there will be a succession of life forms that may arrive by flying, floating or swimming. This new island will be made entirely of crustal material (rock) with little or no evidence of life forms. They begin with a brand new tropical island (produced by an oceanic hot spot or at a plate boundary) and gradually change through thousands of years from a fringing reef, to a barrier reef, to an atoll, and finally to an extinct reef as a seamount or guyot.Ī new oceanic island in the tropics will have no terrestrial or marine life when it is first formed. (LJF images)Ĭlassic coral reef formations change through time. It is the unique relationship (described in the next section on 'The Coral Animal') between these two species that allows coral reefs to grow and exist year after year, providing a place for many other species and the rich habitat of the coral reef.Īerial view of the stages of coral reefs (fringing, barrier, atoll). Hermatypic corals really are a symbiotic combination of a coral animal and an organism called a zooxanthellae. These reefs are built from a unique type of coral called a hermatypic coral and can only exist in warm ocean water. (GA image)Ĭoral reefs are an exception to the lack of life in the marine tropical waters. (There are exceptions where nutrient-rich bottom water surfaces due to upwelling.)Ĭoral reefs have a great diversity of life. This condition, in the tropical ocean, results in a lack of life and low productivity in most areas. So, with a lack of the base of the marine food chain (phytoplankton) there are few zooplankters and few small fish. In turn, they are eaten by larger critters, like small fish, and so on up the food chain. They are the second step in the marine food chain. There is another type of plankton, the zooplankton (animal plankton) that feeds on the phytoplankton. The phytoplankton in the tropics is nutrient limited pretty much year-round. (GA images)Ĭlear, blue tropical water signifies little plankton. These nutrients are not replaced as long as there is a stable thermocline.Ĭlear blue water in the tropics is common as viewed from on top of the water and from under the water. When present in the tropics the phytoplankton rapidly use up any nutrients in the surface water. They need sunlight for photosynthesis so can only be found in surface ocean waters. These plants are called phytoplankton and photosynthesize to grow. In the marine environment the base of the food chain is primarily microscopic marine plants floating in the surface waters. Plants need nutrients and sunlight for proper growth. Thus, the tropical ocean water is warm but nutrient poor at the surface. We often call them 'fertilizers.' The thermocline separates the bottom (cool, nutrient-rich) water from the surface (warm, nutrient-poor) water in the ocean. It is these nutrients (N, P, and K) that are required for plant growth. This decomposition is what releases nutrients (in the form of nitrogen - N, phosphorous - P, and potassium - K) back into the environment. The dead bodies decompose on the bottom of the aquatic environment. In aquatic environments most living organisms sink when they die. This warm water is very comfortable for divers.Ī thermocline locks out nutrients from surface ocean water. This surface (warmer) water stays separated from the subsurface (cooler) water by a layer of water where the temperature rapidly changes with depth (the thermocline). The abundant year-round sunlight and heat warms surface ocean water in the tropics enough so that it has a lower density than the subsurface water. (GA image)Ī thermocline is generally present in the tropical marine environment. The author (Genny) and her family, diving in the tropics. There is almost always plenty of sun, warm sea surface temperatures, and few surface nutrients in the ocean water. This means there are few environmental changes throughout the year and no real seasonal changes in sunlight, ocean water temperature, or surface nutrients. A stable year-round climate is common in the tropical marine environment.
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