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Marine Ecology Progress Series

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MEPS 257:69-76 (2003)  -  doi:10.3354/meps257069

Effect of salinity on growth, pigmentation, N2 fixation and alkaline phosphatase activity of cultured Trichodesmium sp.

Fei-Xue Fu*, P. R. F. Bell

Department of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia

ABSTRACT: Trichodesmium sp. isolated from the Great Barrier Reef lagoon was cultured in artificial seawater media containing a range of salinities. Trichodesmium sp. actively grew over a wide range of salinities (22 to 43 psu) and hence can be classed as euryhaline. Maximum growth occurred with salinities in the range 33 to 37 psu. Chl a content and alkaline phosphatase activity were found to increase with salinity over the range 22 to 43 psu, but the N2 fixation rate was reduced at salinities below and above the range for maximum growth. Growth in media exhibiting maximum growth was characterised by well-dispersed cultures of filaments, while significant aggregations of filaments formed in other media. It is proposed that the tendency for Trichodesmium filaments to aggregate in media with salinities outside the range for maximum growth is an opportunistic response to a deficiency of cellular nitrogen, which results from the reduced N2 fixation rates, and the aggregation occurs in order to enhance the uptake of combined N released within the aggregates and/or the N2 fixation within the aggregates.

KEY WORDS: Trichodesmium sp. · Salinity · N2 fixation · Alkaline phosphatase activity

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