The Ecology of the Tamar Estuary II. Under-Water Illumination

The Zeiss Pulfrich photometer, with its eight spectral niters covering narrow spectral bands within the visible spectrum, has been used to investigate the penetration of light into an estuary under winter and summer conditions. Throughout the visible spectrum, extinction coefficients in Hamoaze are always higher, in winter often very much higher, than in the English Channel. In marked contrast to the open sea, red light penetrates as well or better than green, and blue is cut down most rapidly