Bacterial response to blooms dominated by diatoms and Emiliania huxleyi in nutrient-enriched mesocosms

• Published in: Estuarine, coastal and shelf science Vol. 46; no. suppl. A; pp. 35 - 48
• Main Authors: Sanders, R, Purdie, DA
• Format: Journal Article
• Language: English
• Published: 01.02.1998
• Subjects: Bacillariophyceae; Brackish; Emiliania huxleyi; Leptocylindricus danicus; Leptocylindrus danicus; Marine; Skeletonema costatum
• ISSN: 0272-7714
• DOI: 10.1006/ecss.1998.0329

The bacterial response to two algal blooms dominated by the marine coccolithophorid Emiliania huxleyi and the marine diatoms Skeletonema costatum and Leptocylindricus danicus in nutrient-enriched mesocosms was observed. Bacterial abundance was determined using epifluorescent microscopy and bacterial activity using super(3)H-thymidine and super(3)-leucine incorporation. There were significant differences in the bacterial response to the two blooms with the maxima in bacterial activity associated with the E. huxleyi bloom occurring almost synchronously with the maxima in E. huxleyi abundance and the maxima in bacterial activity associated with the diatom bloom occurring about 1 week after the maxima in diatom abundance. It is suggested that this results from the greater tendency of E. huxleyi to release simple monomeric organic compounds compared to S. costatum. Levels of bacterial super(3)H-leucine incorporation relative to bacterial super(3)H-thymidine incorporation were significantly higher in the diatom dominated bloom compared to the E. huxleyi dominated bloom. It is suggested that this is associated with the large scale exudation of complex polypeptides by S. costatum. In both enclosures bacterial super(3)H-thymidine incorporation peaked rapidly relative to bacterial super(3)H-leucine incorporation implying a bacterial demand for inorganic nitrogen at the peak of bacterial activity. Consequently, at the peak of the E. huxleyi bloom algae may have been competing with bacteria for inorganic nitrogen, whereas during the diatom dominated bloom this competition probably did not occur until the diatom bloom had begun to subside. Following the collapse of both blooms the bacterial community regained its pre-bloom status as a small source of ammonium.