INTRODUCTION Solar radiation is probably the most fundamental ecological factor in the marine environment: it is the source of energy utilized by plants in the manufacture of the complex organic substances upon which the metabolism of the sea depends. The degree of availability of this energy directly controls the amount of organic matter synthesized, for, no matter how favorable other factors may be, this amount will be limited by the relatively low efficiency of the photosynthetic process. An important “by-product” of photosynthesis is the production of oxygen. This contributes appreciably to the amount of dissolved oxygen in sea water and plays an important role in plant and animal metabolism and in the oxidation of inorganic and organic substances. The diurnal light cycle in the photic zone of the sea is, in some organisms, a tropistic stimulus and is the cause of the well-known vertical migrations of certain plants and animals. In addition to these roles, light is also necessary for the formation of certain plant and animal pigments. Solar radiation is likewise responsible for the heating of the oceans, and temperature profoundly affects all metabolic processes in animals and plants. The various wave lengths (different colors) of sunlight range from the infra-red (24,000–760 mμ), through the red (760–650 mμ), orange (650–600 mμ), yellow (600–550 mμ), green (550–500 mμ), blue (500–450 mμ), violet (450–400 mμ), to the ultraviolet (400–280 mμ). In sea water light of different wave lengths is absorbed at different rates,...