The role of benthic microalgae in neritic ecosystems

Benthic microalgae include pennate and centric diatoms, cyanobacteria, chlo rophytes, and other microscopic algae living at the sediment/water interfac e in neritic ecosystems. Increasingly, numerous studies have now documented microalgal production, biomass, and other aspects of their ecology in much of the world's neritic habitats, although substantial gaps in the geograph ical and depth distributions of these studies remain. Analysis of 85 studie s of benthic microalgal production yields a global estimate of annual benth ic microalgal productivity of about 500 million tons of carbon, somewhat hi gher than previous estimates. Information on the depth distribution and com pensation light intensity for benthic microalgae suggests that in many area s productive benthic microalgae extend to depths well below those where the y have been studied. The high biomass concentrations attained by benthic microalgae at the sedim ent/water interface reflect a variety of adaptations and selective advantag es likely to result from those adaptations. Stabilization of the sediment s urface by microalgal growth and extrapolymeric substance production is an i mportant feature of the ecology of benthic microalgae. Regulation of nutrie nt fluxes, gas exchange, and redox conditions may result from microalgal st abilization of the sediments and create conditions more favourable to micro algal growth. Grazing and physical perturbations can act to disrupt the sta bilizing effects of microalgal growth on the sediment surface. These ideas are presented as a new paradigm that proposes a key role for benthic microa lgae in neritic ecosystems along a spectrum of light limitation and physica l disturbance.