Document Type

Article

Department/Program

Virginia Institute of Marine Science

Publication Date

1981

Journal

Bulletin of Marine Science

Volume

31

Issue

1

First Page

164

Last Page

169

Abstract

Primary productivity and nitrogen fixation (acetylene reduction) were estimated in two macroalgae-cyanobacteria associations from coral reef communities. Microdictyon sp., collected at 20 m on the reef proper and Laurencia sp., from 1-2 m on an inshore sand flat, showed high productivity rates: 1.15 and 1.90 mg C g-l h-I, respectively. Dissolved organic carbon excretion for both associations was less than 0.5% of the total carbon fixed. Nitrogenase activity was much higher in the Laurencia association than in the Microdictyofl association (9,61 vs, 1.04 f.Lg N g-l h-1); this probably was due to differences in the cyanobacterial epiflora, The effect of light on the rates of photosynthesis and nitrogen fixation was evaluated for the Microdictyon association. Nitrogen fixation supplied approximately 2% of the nitrogen demand of the Microdictyon complex and 19% of the demand on the Laurellcia complex, In a nutrient poor environment, any de novo nutrient input is of value; for the Laure/lCia association, nitrogen fixation could supply a substantial portion of the nitrogen required for photosynthesis,

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