Submarine daylight and ecology

The different parameters acting upon daylight before it reaches underwater organisms are discussed. Methods for measuring these parameters are reviewed, and lightsensing units equipped with hemispherical collectors and possessing a narrow spectral sensitivity band are recommended for use in marine biology. A new formula relating Secchi-disk readings to attenuation coefficients is proposed. A method is suggested which makes it possible to calculate the yearly amount of radiant energy reaching an underwater station. Possible sources of error are surveyed.