The tropical diazotrophic phytoplankter trichodesmium: biological characteristics of two common species

• Published in: Marine ecology. Progress series (Halstenbek) 1993, Vol.95 (3), p.295-304
• Main Authors: Carpenter, Edward J., O'Neil, Judith M., Dawson, Rodger, Capone, Douglas G., Siddiqui, Pirzada J. A., Roenneberg, Till, Bergman, Birgitta
• Format: Article
• Language: English
• Subjects: Buoyancy; Carbon; Chlorophylls; Cruises; Cyanobacteria; Luminous intensity; Marine; Oceans; Photosynthesis; Pigments; Respiration
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps095295

The 2 tropical cyanobacterial species Trichodesmium thiebautii and T. erythraeum had similar photosynthetic characteristics in the southwestern Sargasso Sea and Caribbean Sea, with mean rates of light saturated photosynthesis (using O2 electrode) of 42 (SD = 21.3) and 37 (SD = 18.4) mg O2 mg chl a−1 h−1 at 1410 μE m−2 s−1 respectively over a 1300 n mile cruise track. Rates of dark respiration were high, and the compensation point for both species was 150 μE m−2 s−1 (ca 55 m, midday). Estimates of carbon doubling times (using photosynthetic quotient) were from 3.0 to 3.8 d based on expected photosynthetic rates in the water column. The mean rate of nitrogenase activity at 300 μE m−2 s−1 by T. thiebautii averaged 0.45 nmol ethylene colony−1 h−1, 1.6 times that of T. erythraeum (p < 0.01) as observed from samples collected on 3 cruises (64 paired observations). Furthermore, in a comparison of nitrogenase activities, at light intensities between ca 500 and 2500 μE m−2 s−1, T. thiebautii was about twice as active as T. erythraeum. The phycoerythrin content of T. erythraeum averaged 260 ng colony−1, 4.4 times that of T. thiebautii, and the mean PE: chl a ratios were 3.2 and 1.2, respectively. Other pigments: (β-carotene, zeaxanthin, myxoxanthophyll, echinenone, and trace pigments) were similar between the 2 species. The organization of subcellular inclusions was distinctly different in these 2 species. The high abundance of T. thiebautii relative to T. erythraeum in many tropical seas may be due to higher rates of N2 fixation and a previously reported neurotoxin in the former species.