Monterey Bay Aquarium Research Institute
Marine Botany

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Mastocarpus Morphology and Anatomy

COLORS: Mastocarpus is typically reddish-black in the Monterey Bay area, though descriptions indicate the color ranges from this reddish-black to an olive brown. This color description goes for the tetrasporophyte and female gametophyte stages. The male gametophyte can be anything from a bright yellow to a light pink. This coloration possibly reflects minimal pigment expendature in a transient stage of the alga.

SHAPES: Mastocarpus' tetrasporophyte is so different from the gametophytes that is was thought, until recently, to be of a different genus, Petrocelis. It is crustose in form, resembling tar awash on the rocks. The crusts are reported to get up to 1 meter in diameter, usually around 5 cm, and they are typically 2 - 2.5 mm think.

The morphologies of Mastocarpus' gametophyte stages vary from plant to plant and even thallus to thallus on a single gametophyte (see photo.) The female gametophyte thalli are dichotomously branched and typically 5 - 7 cm in length with width highly variable, 1 - 5 cm. Female thalli are densely covered with small 1 - 2 mm diameter papillae.

The papillae are roughly spherical in shape, growing from small bumps to 1 - 2 mm balls on the thallus surface, sometimes contacting each other as they ripen. These papillae are cystocarps, housing the growing carposporophyte (a separate generation) as it matures.

The male gametophyte is also highly variable, sometimes resembling Ulva, the sea lettuce in form.Once mature, the male gametophyte usually falls apart, aiding the dispersal of spermatia (formed by spermatangia). No papillae are produced.

There are no motile stages of any red algae. This includes all spores and gametes. Because of this fundamental difference from the other algae, red algal gametes are given special names: spermatia for males, and carpogonia for females.

MICROMORPHOLOGY: Mastocarpus, despite odd macromorphologies, is a typical filamentous red alga. The tetrasporophyte and gametophytes are composed of well-ordered filaments of cells, while the carposporophyte is more an irregular mass. The crustose tetrasporophyte stage gets some mechanical support from cross-linking connections between filaments. The tetrasporophyte and gametophytes are covered in a thin cuticle that protects the underlying cells from desiccation and also holds them together. Some other red algae show an ability to shed the cuticle to rid themselves of epiphytes, but Mastocarpus is apparently unable to do this.

Image above by J.L. Connor; Mastocarpus pages copyright W. Ludington 1999