MICROPHYTOBENTHOS - THE ECOLOGICAL ROLE OF THE SECRET GARDEN OF UNVEGETATED, SHALLOW-WATER MARINE HABITATS .2. ROLE IN SEDIMENT STABILITY AND SHALLOW-WATER FOOD WEBS

The microphytobenthos form an important component of all shallow-water ecosystems where enough light reaches the sediment surface to support appreciable primary production. Although less conspicuous than macroa lgae or vascular plants, the microphytobenthos can contribute signific antly to primary production and can modify habitat characteristics. Th e microphytobenthos alter sediment properties (e.g., erodibility) both directly, in the extreme forming a mat or scum on the sediment surfac e, and indirectly by modifying the activities of benthic infauna (e.g. , pelletization, burrowing, tube building; and sediment tracking). Car bon dioxide fixed by the microphytobenthos supports higher, grazing tr ophic levels. These include deposit-feeding and suspension-feeding mac rofauna as well as meiofauna and microfauna. Quantitative relations be tween the feeding and growth rates of macrofauna and the abundance of microphytobenthos and suspended organic matter (i.e., functional respo nses) are reviewed. Given the current state of knowledge of the direct and indirect interactions involving trophic dynamics, sediment proper ties, and benthic microalgae, we argue for reductionist studies of par ticular interactions as distinct entities. This is a prerequisite for the emergence of a comprehensive picture of unvegetated ecosystems and the ability to predict their responses to man's activities.