Marine Biology

LIGHT

The availability of light in the marine ecosystems plays a major role , mainly in the process of photosynthesis by plant communities in the sea. Light that is falling or penetrating into the seawater is absorbed by the microscopic as well as macro vegetation like seaweeds and synthesise organic matter . This is called primary production, with which the consumers of the higher trophic levels of the marine food chain depends for their food. When there is good light, then there will be a good amount of plants and hence good organic matter, which determines the distribution of animals in the sea. The vision of the marine animals is also controlled by the light availability and also light plays an important role in the breeding cycles of the many marine animals.

Of all the light rays emitted by the sun is not fully reaching the ocean surface and only 50% of it striking the ocean surface. The rest of the sun light is scattered, absorbed or reflected back into the atmosphere. The reflection of the same depends up on the various factors like angle of incidence of sun light on the ocean surface, seasons of the year, the time of the day and the location or latitude. In the equator, the sun light radiation is fairly constant throughout the year when compared to the higher latitudes. That is at near the poles, the availability of sunlight is continuous during the summer and a continuous darkness in winter seasons.

Of all the light falling on the surface , only 1% of the falling light will be penetrating down the sea and the remainder is absorbed and is scattered by the particles suspended in the water. The penetration of light also varies with the wave lengths of the light. Not all the rays are penetrating deep in the water and some of them are absorbed in the top few meters of the water column. Red light is absorbed in the top few meters depth whereas the blue light rays penetrates up to a depth of about 150 meters in the sea. The penetration of light is also influenced much by the turbidity or clarity of the water. If the water is more turbid in nature, the most of the light will be absorbed in the top few meters of depth whereas in the clear waters it will penetrate to the deeper levels of the sea i.e about 1000 m depth.