Green macroalgae of the genus Codium are, I think, more often encountered as accidental but benign introductions into our reef tanks, than deliberately purchased as ornamental saltwater plants. Nonetheless Codium sp. algae are deliberately traded, although without precise identification; but I have seen Codium edule traded. C. edule is a hardy enough seaweed from the tropical region from Indonesia to Hawaii, and it's natural ecology explains its harfiness. More than one species is traded as just 'Codium'; not all details can be generalized to the entire genus. But C. edule is more precisely understood.
C. edule commonly grows intertidally as a mat attached to rubble of rocks, coral, and broken shells. It has a fleshy, spongy texture, and is also known as the branched sea cushion. It can also be found in subtidal habitat, for instance on shallow reefs that are subject to atypical salinity. Intertidal pools, too, are subject to variations of salinity because they are isolated from the ocean for hours, and suffer both rainfall and evaporation. They are difficult habitats for marine life to survive in, because they are unstable environments, even over the course of the day. C. edule is is this able to colonise habitats where other seaweeds might have difficulties surviving.
In the aquarium, C. edule is also adaptable to different strengths of aquarium lighting, but it has a marked preference for high dissolved organics, as is typical in natural rock pools. But C. edule is not the fastest growing of all seaweeds, and this might explain why it is not among he most popular seaweeds available to aquarists, who like to grow rampant species for practical nutrient export, and often relegated to the sump. Yet for those of us who appreciate the beauty of macroalgae, C. edule is suited to growing around the aquascape in the way freshwater aquarists apply freshwater mosses and liverworts in planted tanks.
