The water in the Caribbean appears blue because it absorbs the red, yellow and green wavelengths of light while reflecting the shorter blue wavelengths of light. The Caribbean water is very clear due to the absence of suspended particles and plankton, further increasing the blue color.
In areas of the ocean where the water has large levels of plankton, the water takes on a green color. Plankton uses chlorophyll to produce food through photosynthesis. Water suspends plankton, causing it to reflect more of the green light that occurs in tropical areas such as the Caribbean.
There is a cost to the clear, blue water of the Caribbean, however. Plankton is the base of the food web for ocean life. In these blue waters, life is harsh, and the creatures living there must adapt to living in a nutrient-poor ocean.
Observers see these adaptations in the coral reef. Coral are living creatures that form the bony structure for the underwater community. The reef provides hiding places and draws in other ocean life. The coral reef ecosystem reduces the harshness of tropical ocean life without affecting the color of the water.
In some shallow areas, the water takes on an aqua color due to the reflection of the sunlight on the sand at the bottom of the ocean. However, in areas where the water is deeper, most of the light is absorbed as energy by the water long before it has a chance to reflect from the bottom of the ocean.