In addition to the red or crustose coralline algae, some other simple marine algae secrete carbonate in tropical seas. Secretion of aragonite by Halimeda discoidea Decaisne, a calcareous green alga, and Padina japonica Yamada, a calcareous brown alga, was investigated in shallow Hawaiian waters. Along traverses between reef and shore, Padina is most abundant close to shore, whereas Halimeda flourishes in the deepest water, generally midway between shore and reef front. In Padina, the proportion of calcium carbonate to total body weight is inversely proportional to abundance of the algae on the sea floor, whereas for Halimeda the proportion is directly related to relative abundance. For Halimeda as much as 70 per cent of the body weight may be aragonite.

Production of calcium carbonate and of total organic material has been compared for shallow water specimens, for specimens dredged from deeper water, and for calcareous and noncalcareous algae described by Doty recently. Aragonite secreted by algae contributes an important volume of material for subsequent diagenesis in tropical carbonate sediments that are ultimately converted to limestones.

End_of_Article - Last_Page 273------------