Algal Biomass Accrual Research Articles

Effect of primary producers on the heterotrophic metabolism of a stream biofilm

1. ,The influence of benthic algae on heterotrophic metabolism in a forested Mediterranean stream was investigated. Bacterial density and ectoenzymatic activities, as well as algal biomass (chlorophyll‐a) and metabolism (the rate of 14C incorporation), were measured during colonization over 60 days of artificial substrata (clay tiles) under light and dark conditions.2. ,Chlorophyll‐a and the rate of 14C incorporation were significantly higher in light‐grown than in dark‐grown biofilms. Bacterial density and ectoenzymatic activity (especially β‐glucosidase) were also significantly higher in light‐grown biofilms.3. ,Regressions of chlorophyll‐a and 14C incorporation values on the ectoenzymatic activities were significant. The slopes of regression lines obtained for dark‐grown biofilms were significantly higher than those obtained for light ‐grown biofilms.4. ,The differences in the slope (of the regression lines) between dark and light‐grown biofilms suggest that the response of the heterotrophs is faster in biofilms with low algal biomass accrual and slows down when algal biomass is increased.5. ,It is concluded that algal accumulation in the epilithic biofilm influences the use of organic matter by the heterotrophic community by increasing the amount of organic substrate available for bacteria.

Effects of Ambient Ultraviolet Radiation on Littoral Periphyton: Biomass Accrual and Taxon-Specific Responses

Ultraviolet (UV) radiation levels were manipulated in the littoral zone of a low-elevation, mid-latitude glacial lake. Benthic algal biomass accrual was significantly inhibited by ambient levels of W radiation early in colonization, but after 45 days of accumulation, the biomass of W-exposed and W-shielded algal communities did not differ significantly. Algal taxa differed in their sensitivity to UV radiation. Cell densities of Synedra ulna, S. radians, Cyclotella comensis, and the Epitherniaceae were significantly reduced by ambient UV radiation. Achnanthidium minutissimum appeared to be stimulated by exposure to UV radiation. Differential responses of diatom taxa may have important implications for littoral zone food webs.