Diffusive limitation of C and nutrient uptake can be an important factor regulating metabolic processes in aquatic plants. Relationships between the flow regime and both primary productivity and nitrogenase activity (ethylene production) of coral reef algal components were studied via a productivity chamber that simulates oscillatory flow. Net primary productivity of algal turfs was increased significantly by flow speeds (steady flow equivalent) up to 16 cm s-l. The mode of water flow also was important; primary productivity of algal turfs increased by 2 1% under an oscillatory flow regime as compared to vortex flow created by stirring. Acunthophora spicifera exhibited increased primary productivity at flow speeds up to 10 cm s-l, while primary productivity of another rhodophyte, Coelothrix irregularis. increased up to 4 cm s-I. Rates of nitrogenase activity exhibited by algal turfs also were affected significantly by flow speed. These data indicate that diffusive limitation is important to varying degrees in reef algal turfs and macroalgae and suggest that primary productivity and rates of nitrogenase activity depend on ambient flow speeds and boundary-layer dynamics.Estimates of metabolic rates for marine organisms are essential to the understanding of trophic web structure and energy and material transfer in marine environments. Calculations of primary and secondary productivity for marine communities often rely on chamber measurements of metabolism. Estimates of respiration and photosynthesis most often are made from measurements of carbon or oxygen flux over time when the organism is confined in an enclosure. Although the techniques to estimate the rates of C fixation and respiration have become more sophisticated, the organism under --

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Chemical treatments similar to those routinely used to extract cellulose from plant biomass caused significant increases in the relative crystallinity index (RCI) of Sig-macell 100 (a commercial cellulose of moderate crystallinity), as measured by x-ray powder diffraction in both the reflectance and transmittance modes. In general, the largest increases in RCI were observed following higher (rather than lower) temperature treatments. Substantial increases in crystalliity were also observed upon resuspension in water prior to drying, with higher temperatures again resulting in the greatest increases in RCI. Measurement of the RCIs of wetted Sigmacell 100 samples by acid hydrolysis kinetics revealed that most of the increased crystallinity occurred rapidly upon contact with water. In contrast to Sigmacell 100, a cellulose of higher initial crystallinity (the microcrystalline cellulose Sigmacell 50) showed little change in crystallinity following the above treatments. The results provide a partial explanation for the inconsistent relationships reported between cellulose crystallinity and cellulose biodegradation. (c) 1995 John Wiley & Sons, Inc.