Growth and calcification of the freshwater cyanobacterium Rivularia haematites

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Abstract
The radial growth rate and calcification of a cyanobacterium, Rivularia haematites , has been measured in detail for the first time. Maximum radial growth rates of 12–14 μm d –1 were recorded during the summer and minimum rates of less than 2 μm d –1 during winter. There was a significant correlation ( p < 0.001, r = +0.929) between radial growth and water temperature. Differences in growth between sites were related to variation in water temperature and illumination. All colonies were heavily calcified and two patterns of calcification were noted: (i), a broad, seasonal band formed at the colony surface with calcification proceeding inwards, resulting from inorganic precipitation within the mucilage, probably augmented by particle trapping; and (ii), a series of finer secondary bands, probably formed as a result of photosynthetic activity within meristematic zones of the colonies. Colonization by Rivularia and its tolerance to emersion are also discussed briefly.