Blue-Green Algae (Myxophyceae)

This class contains only small, poorly organized plants, some consisting of only a single cell, while others are multicellular. The blue color of these plants is due to a water-soluble accessory pigment, phycocyanin. In certain inland waters, it has been reported that upon the

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death of large masses of a blue-green alga (Anabaena), the water-soluble pigment may impart a deep-blue color to the waters. The Red Sea owes its name to a free-floating form, Trichodesmium erythraeum (fig. 68a), which has a red accessory pigment and is responsible for the red color sometimes observed in the surface waters. Thus, “blue-green algae” may be red. The cell walls of plants of this group consist usually of chitin, instead of the cellulose so characteristic of other plants; therefore, in a small measure, they supplement the enormous quantities of chitin produced in the sea, especially by the crustacea. Some Myxophyceae are endophytic; that is, they live within the bodies of other plants in an association known as symbiosis. A marine species, Richelia intracellularis, may be found within the cells of the diatom Rhizosolenia.

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Methods of Reproduction. Reproduction in this group is by asexual fission. This, the most simple method of propagation, consists of single individuals dividing to form two of lesser size, which in turn again divide after growth. In instances involving blue-green algae that form chains of cells, the chains divide into smaller sections known as hormogonia. Fission of the cells in the hormogonia again increases the length of the filaments.

Distribution. The Myxophyceae are of less general importance in the oceans than are the following algal groups. They are widely distributed in fresh and brackish water. In the sea they are most often found in the warmer waters, where they may cause the phenomenon of sliming. A brackish-water form, Nodularia spumigena, native to calm fjords of the north, may at times cause extensive sliming of the waters. In the Gulf of Bothnia, sliming due to this or similar forms may assume considerable proportions.