Species description

Care, breeding and tankmates

Plant profile

Placement

Midground

It serves as a highly unique, sculptural focal point in the marine display aquarium rather than a functional refugium plant. It should be placed in areas with moderate, turbulent water flow to prevent detritus from settling on its velvety surface. It thrives under moderate lighting, as excessively intense reef lights can encourage competitive nuisance algae to grow upon it.

Botanical form

Algae

This fascinating organism is actually a coenocytic algae, meaning it is a giant, multi-nucleated single cell with no internal cell walls. It forms thick, spongy, cylindrical branches that bifurcate (fork) repeatedly, resembling thick green fingers or branching antlers. The surface has a distinct velvety, dark green texture that is soft to the touch.

Growth

Slow

Codium fragile exhibits a notably slow growth rate compared to most other marine macroalgae. It slowly extends its branches and thickens over a period of many months, making it very easy to manage in a display tank. Its slow growth means it is not an effective candidate for active nutrient export in a refugium.

Substrate

Low

It does not require a deep sand bed or specialized soil, as it attaches itself to hard surfaces using a disc-like holdfast. It is typically found growing on rocky outcrops, shells, or coarse coral rubble. It should never be buried in the sand, as the buried portions will quickly succumb to bacterial rot and foul the aquarium.

Column fertilization

None

While typical marine fish bioloads provide adequate macronutrients, occasional dosing of a specialized marine algae trace element supplement is highly beneficial. This ensures the structural integrity of the spongy branches remains strong. Care must be taken not to over-fertilize, which would fuel the growth of faster, competitive algae species.

Root fertilization

None

As a marine algae, root fertilization is entirely inapplicable and irrelevant. The holdfast is purely for mechanical attachment and has no absorptive capabilities. All nutrients must be maintained and balanced within the water column.

Trimming

Occasional

Maintenance requires very little effort due to its slow growth. If it becomes too large, it can be carefully pruned by cutting off sections of the "fingers" with sharp scissors. Ensure that cuts are clean to prevent the remaining tissue from rotting, and remove the trimmed pieces to export the absorbed nutrients.

Propagation

Fragmentation

Propagation is straightforward but must be done carefully. You can use a sharp, sterile blade to cut a branch at a bifurcation point. The severed branch can then be gently tied to a piece of live rock or a frag plug using fishing line, where it will slowly develop a new holdfast and continue growing.

Sensitivity

Sensitive

It is sensitive to large fluctuations in salinity and temperature, requiring stable marine conditions to survive. It can quickly decline or "melt" if nutrients drop to absolute zero or if it is smothered by detritus or competitive microalgae. Some herbivorous fish and invertebrates, such as certain urchins or large tangs, may graze on it.

Layout role

Macroalga / Refugium

In a marine display tank, Codium fragile adds a fantastic dark green contrast and a highly unusual, spongy texture to the aquascape. It works well as an accent piece among live rock or mixed macroalgae displays. It provides excellent shelter for small pods and invertebrates, adding to the biodiversity of the tank.