Monterey Bay Aquarium Research Institute
Marine Botany

Life History of Articulated Coralline Algae

diagram of coralline life history

       The articulated corallines have an isomorphic, three-stage life history. Like many other red algae, the geniculates have structurally identical tetrasporophytes and gametophytes, with an intermediate parasitic carposporophyte stage. Both tetrasporophytes and carposporophytes are diploid life stages, while gametophytes are haploid. Meiosis occurs in the sporophytes, leading to the eventual release of haploid tetraspores. After these spores settle on a rocky substrate, they develop into male or female gametophytes. Fertilization occurs in an oogamous manner with non-motile carpogonia being fertilized by non-motile spermatia. Fusion of the pronuclei of these haploid gametes results in the restoration of the diploid state and intiates development of the carposporophyte, which produces carpospores. Fruiting carposporophytes release diploid carpospores, which develop into tetrasporophytes. 

carposporophyte

A carposporophyte within a female conceptacle.

       Because female and male gametophytes and tetrasporophytes are morpologically identical, the easiest way to distinguish amongst them is by sectioning and examining conceptacular content with a microscope. The conceptacles of male gametophytes will house spermatangia whereas female gametophytes' conceptacles will contain carpogonia and/ or parasitic carposporophytes. Zonate tetraspores will be found in tetrasporophyte conceptacles. There is no easy way to determine the life stage of a given articulate. The contents of a specimen's conceptacles are the best indicator of whether or not it is a gametophyte or tetrasporophyte. 

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© 2001 Ian Ehrenreich. All rights reserved.