Codium: Biology of a Marine Invasive

Multinucleated Single Cell Green Alga

Codium fragile is a large, dark green macroalga with one to several, thick upright branches arising from a broad, spongy basal disc attached to the substrata.  The cylindrical branches are dichotomously branched and arise from a juvenile phase having both prostrate and erect branches.  Fronds are generally annual, dying back in the Winter and arising from the perennial basal portion in the Spring.

 

The branches are constructed of interwoven coenocytic filaments, all derived from the same germ cell. Like Bryopsis (January 2013 post), there are no cell walls to separate nuclei or individual cells.  However, the structural organization of Codium is distinctly different from Bryopsis and other coenocytic green algae.  Each multinucleated branch is composed of a network of fibers that orient pointed cellular extensions, called utricles, toward the outside.  The utricles of Codium fragile have a thorn-like projection that is absent in other species. The utricles are packed tightly, side by side, creating an outer layer surrounding the filaments. 

Codium has been grown in the laboratory to study differentiation and regeneration.  In early studies, cultures were primarily composed of dissociated branched, coenocytic filaments. The typical growth form of upright branches with utricles did not develop.  With further research, techniques to grow mature filaments and branches were developed.  Branched algae were developed from heterotrichous juveniles when cultures were agitated on a shaker. The shear forces created by mechanical agitation were essential for both initiation and maintenance of upright branches.  Using aquaculture techniques, Codium has been grown in Korea from regenerating isolated utricles and medullary filaments in a step-by-step manner (see LINK below).   

Codium fragile

 Codium fragile growing on the side of a floating dock at MacMillan Wharf, Provincetown, MA. Photo was taken during a monitoring session in August, 2013. Codium typically grows along the water line in the same location as Ulva, Enteromorpha, and other green algae.

The Life Cycle of Codium

Diagram of the life cycle of Codium showing upright thallus, cross section through a branch, utricles, gametes, and dichotrichous germling.  The cross section through the branch (fertile thallus, bottom left) shows the central filamentous multinucleate cell and the outer utricles.  Male and females gametes fuse together to form the zygote, which then develops into a germling that grows to form the holdfast and diploid thallus. 

Codium fragile Internal Structure

 

Diagram of a cut Codium branch showing central filaments and the outer utricles.

Microscopic Structure Codium fragile utricles

 Left, diagrams of Codium utricles showing fusiform gametangia forming at the side of the utricle. Microscopic image of Codium utricles.

 

LINKS:

Dixon, HH.  Structure of Codium.  Ann Bot 11: 588-590, 1897.   

Ramus, J.  Differentiation of the green alga Codium fragile.  Amer J Bot 59: 478-482, 1972.

MH Yang, G Blunden, FL Huang.  Growth of a dissociated, filamentous stage of Codium species in laboratory culture.  J Applied Phycol 9:1-3, 1997.

Hwang, EK, JM Baek, and CS Park. Cultivation of the green alga, Codium fragile (Suringar) Hariot, by artificial seed production in Korea. J Appl Phycol 20: 469-475, 2008.

Aquaculture of Codium fragile.  b-d) filaments are grown on coiled fibers for about 6 weeks.   e) with continued culture, erect thalli develop. f-h) once erect thalli develop, the fibers are coiled around a larger culture rope.  Small branched plants are formed by 5 months (g) and mature growth is achieved by 7 months (h). 

Encyclopedia of Life (EOL):  Codium fragile
Natural History of Sado Island, Japan:  Codium fragile.
Flora of South Australia:  Codium fragile (Suringar) Hariot

Natura In Neustria:  Codium fragile (algue verte)
Taxonomic Toolkit For Marine Life of Port Phillip Bay http://portphillipmarinelife.net.au

Codium on the beach at Port Phillip

Montery Bay Aquarium Research Institute: Codium setchellii. Structure of C. setchellii compared to C. fragile.