Why are the waters of the Caribbean so clear and the fish so colorful? The answer is a combination of several factors including light absorption, depth, temperature, and microscopic phytoplankton. Warmer water has less oxygen then colder, the higher the water temperature the lower the amount of oxygen and hence the higher transparency of the water. Phytoplankton, plants like algae, require nitrogen and phosphorous as food and there’s not much in the warm waters of the Caribbean. Fewer floating microscopic life forms mean less muddled and crowded currents, and therefore much clearer water. In addition, since much of the Caribbean is quite shallow, little thermocline movement of waterborne nutrients for algae growth occurs between different temperature layers as it does in the Atlantic.
Light absorption also helps color the water. Sunlight, composed of electromagnetic radiation in colors from red to blue, is scattered by particles suspended and vibrating in the water. The shorter blue wavelengths scatter more effectively and are absorbed less rapidly than the longer red and orange wavelengths. Seawater appears blue for about 100 feet under the surface, and then becomes black with the absence of light. In essence, the sunlight performs a native dance with the warm and shallow water of the Caribbean to account for the blue hued sea. The blue tones bounce back to the surface making them more visible than the others. You can see the same effect in snow and ice that often appears bluish. By contrast the Red Sea is red because it contains algae that release reddish-brown pigments; the Yellow Sea is yellow because rivers fill it with blonde colored mud; and the Black Sea is black because it is essentially landlocked, resulting in little oxygen near the surface and a bottom filled with hydrogen sulfide.
The pristine Caribbean waters provide the perfect backdrop for the multi-hued fish gliding through it. Vivid colors on land might mean “I’m dangerous or bad-tasting” — yet most brightly colored reef fish are actually pretty tasty to us humans. Bright colors might help fish attract mates, but most fish, male to female, are equally colorful. Bright colors might camouflage and/or identify fish in the multi hued environment of the coral reefs. Different patterns might also limit inter-species aggression since fish usually don’t fight with their relatives. These and other less well-known theories are studied and researched, and as such are still just scientific conjecture. However, you also need to know, that fish don’t see as we do and they recognize colors that humans don’t. In fact, research has shown that this ability to perceive colors even differs between fish species. Most big predator fish are colorblind and can’t pick up on small movements, since they don’t care what color their prey is and don’t “eat small.” Nocturnal fish react to a different spectrum then diurnal, and it’s fascinating that fish see UV colors we can’t, so what we perceive is not what they focus on. In fact, some Caribbean species can emit UV signals like ocean fireflies that can turn a school of fish on a doubloon in reaction to an incoming predator. Numerous Caribbean fish also have UV markings that are beyond human perception, and so is it all an illusion?
Furthermore, the clarity of the fish’s waters has had a huge evolutionary influence. As a result, the fish in the Pacific and Atlantic are not nearly as resplendent as those flashes of color from the Caribbean. Dark matches dark, bright matches bright. The fish and the waters of the Pacific and Atlantic are muddier and darker. There you won’t see the bright reds, oranges, yellow and blues displayed by tropical fish. Instead, your catch is markedly brown, white and black. These fish also display simpler designs lacking the intricate dots, swirls, lines and shapes of the warm water varieties.