MEPS 187:77-87 (1999)  -  doi:10.3354/meps187077

Competition between benthic cyanobacteria and diatoms as influenced by different grain sizes and temperatures

Frank Watermann1,*, Helmut Hillebrand2, Gisela Gerdes1, Wolfgang E. Krumbein3, Ulrich Sommer2

1Institute for Chemistry and Biology of the Marine Environment, Marine Station, Schleusenstr. 1, 26382 Wilhelmshaven, Germany
2Institut für Meereskunde, Abteilung Meeresbotanik, Düsternbrooker Weg 20, 24105 Kiel, Germany
3Geomicrobiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University, Box 2503, 26111 Oldenburg, Germany

ABSTRACT: An experimental laboratory set-up was used to study the influence of different grain size compositions and temperatures on the growth of benthic cyanobacteria and diatoms, and on the competition between these 2 groups. Monospecific cultures of 3 species of cyanobacteria (Merismopedia punctata, Microcoleus chthonoplastes, Oscillatoria limosa), and of 2 species of benthic diatoms (Phaeodactylum tricornutum and Nitzschia sp.) were used. The organisms were cultured in 100 ml flasks filled with medium and 3 different kinds of sediment: (1) Sand (fine sand, 63 to 200 µm), (2) Mud-I (mixed fine sand and mud <63 µm in the ratio 80:20 wt %), (3) Mud-II (mixed fine sand and mud in the ratio 50:50 wt %). Experimental temperatures were 10, 15 and 25°C. At 10°C and 15°C, both diatom species achieved the highest biomass on the sediments of the finest grain size (50 wt % < 63 µm) while cyanobacteria achieved low biomass levels. Coarsening of sediments at the same temperature levels revealed a gradually lower biomass of the diatoms. Particularly on sand, the diatoms never reached the same concentrations of chlorophyll a as on mud. The cyanobacteria, on the other hand, had the highest biomass on sand at 15°C. In the competition experiments the benthic diatom species Nitzschia sp. dominated all types of sediments at 10°C and 15°C. The experiments at 25°C were dominated by the filamentous cyanobacterium M. chthonoplastes. This indicates the importance of abiotic conditions for the distribution and abundance of benthic phototrophic micro-organisms.

KEY WORDS: Competition · Cyanobacteria · Diatoms · Temperature · Sand · Mud

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