Marine & AlgaeIntermediate🌗 Medium light

Codium (dead man's fingers)

Codium fragile · also called Dead man's fingers, Green sea fingers, Oyster thief, Green fleece, Sea staghorn, Codium

🐾 Pet-safe

Generally non-toxic to cats and dogs.

Codium is a green macroalgae that grows as soft, dark-green, dichotomously forking finger-like fronds with a distinctive spongy, velvety texture — hence "dead man's fingers." It is an attractive, slow-to-moderate display macro for refugiums and macro tanks. Note the wild species (especially the subspecies C. fragile ssp. tomentosoides) is a notorious invasive on Atlantic coasts.

Educational only. KinStation content is reviewed by licensed veterinarians but cannot replace an in-person exam. Always consult a licensed veterinarian or board-certified specialist for diagnosis, treatment, or any decision affecting your pet's health.

Quick facts

Category	Marine & Algae
Family	Codiaceae
Native origin	Native to the Pacific around Japan; now widely naturalized (and invasive) on North Atlantic coasts and beyond
Care difficulty	Intermediate
Light	Medium light
Pet toxicity	Pet-safe

Light

Medium reef/refugium lighting. It is a green alga (Chlorophyta) that does well under full-spectrum LEDs at moderate PAR; it does not need intense light. Steady lighting keeps the fronds a healthy dark green and firm.

Water

Standard reef parameters: temperature 20-26 C (68-79 F) — it tolerates cooler water than many tropical macros, reflecting its temperate origin; salinity ~1.025 SG, pH 8.1-8.4, alkalinity 8-11 dKH. Consumes nitrate and phosphate. Iron and trace elements support growth. No CO2 (marine).

Soil & potting

Attaches to rock and hard surfaces with a basal holdfast (in the wild it is infamous for clamping onto and lifting shellfish, the 'oyster thief' habit). In the aquarium it is wedged onto or glued to rockwork. Not buried; no aquasoil or root tabs — it feeds from the water column.

Environment — humidity, temperature, placement

Submersed only. No CO2 (marine). Moderate flow keeps the spongy fronds clean. Used as a display macro in the midground; its branching shape adds structure to a macro tank. Reef-safe with corals and fish.

Propagation

Propagated by cutting a section of frond and attaching it to new rock; it also regenerates readily from fragments. This same regenerative vigor is exactly why the invasive subspecies spreads so aggressively in the wild, so contain trimmings carefully.

Toxicity detail

Reef-safe and non-toxic to fish, corals, and shrimp in the aquarium. The key concern is invasiveness, not toxicity: Codium fragile (subsp. tomentosoides, the 'oyster thief') is a recognized invasive species on the coasts of the North Atlantic — eastern North America and parts of Europe — where it smothers shellfish beds. Never release it or its fragments into the wild; dispose of excess in the trash.

Growth stages

How this plant changes through its life — each stage often has its own care, diet and space needs.

Photo coming soon

Spore / recruit

Aquatic plants and macroalgae establish from spores, seeds, or drifting fragments that settle and attach to substrate or rock. Many freshwater aquarium plants and marine macroalgae also spread readily from a detached piece that takes root or holdfast.

Photo coming soon

Young growth

Young growth puts out its first blades, fronds, or leaves and anchors with roots or a holdfast. Submersed plants may look different from their emersed form, and growth speeds up as the plant adapts to the water's light and nutrients.

Photo coming soon

Mature

A mature aquatic plant or macroalga reaches its full size and characteristic shape, forming the dense growth, runners, or fronds typical of the species. Established plants spread to fill space and can be divided or trimmed to propagate.

Reviewed and signed off by: KinStation Editorial — pre-launch draft (pending horticulture review) on 2026-06-10

Sources

Codium fragile - Wikipedia (encyclopedia)
Dead Man's Fingers (Codium fragile) - MosaicMacros (care guide)