5 - Effects of Light

Abstract

This chapter examines the effects of light on benthic algae. Light is a fundamental variable for benthic algae, allowing these organisms to photosynthesize inorganic compounds into living biomass. Photosynthesis responds quantitatively to changes in light. Environmental variation in its quantity and quality potentially accounts for much of the variation in the physiology, population growth, and community structure of benthic algae. Other environmental factors such as substrate stability, temperature, nutrients, and grazers may influence the distribution and abundance of benthic algae, but adequate light is clearly a prerequisite for a phototrophic existence. Benthic light environments are diverse, ranging from full sunlight in shallow, clear waters, to near darkness in deep or turbid habitats. Microenvironments within benthic communities also vary tremendously with depth in the matrix; self-shading and scattering by inorganic particles can reduce light penetration to a few millimeters. Responses by benthic algae to spatial and temporal light variation are not particularly well documented, and need much more attention. The depth distribution of benthic algal biomass does not appear to precisely follow the exponential decrease in light intensity with depth; other depth-related factors such as wave disturbance, nutrients, or temperature may interact with light to govern algal depth distribution.