BLUE‐GREEN ALGAE AND CARBONATES—SCHIZOTHRIX CALCICOLA AND ALGAL STROMATOLITES FROM BERMUDA1

Abstract

Algal stromatolites (laminated sedimentary structures) have been studied in the process of formation in subtidal areas of Bermuda. The primary organism responsible for forming these structures is the blue‐green alga, Schizothrix calcicola. Laboratory studies of the formation of nonlaminated algal mats by unialgal cultures of S. calcicola showed that this species could bind sediment particles. The roles of S. calcicola and a secondary species, Oscillatoria submembranacea, in stromatolite formation have been examined.Since S. calcicola exists planktonically, it can be cultured from water samples. These cultures, and the presence of this species on various substrates in subtidal, intertidal, and supratidal areas indicate its wide distribution in Bermuda inshore waters.The distribution of S. calcicola and other filamentous cyanophytes, as well as consideration of physical factors of the subtidal environments, indicates that the latter probably control distribution of the Bermudian algal stromatolites.Reports of developing algal stromatolites from intertidal areas in other parts of the world indicate that S. calcicola is of major, if not primary, importance in the formation of stromatolites everywhere.