velvets exposed intertidal rock faces

Size
Height: 5–15 cm
Lifespan
2–5 years
Diet
Photosynthetic. Draws energy from sunlight and nutrients from surrounding water. Requires clean water and good flow.
Habitat
Grows on rocky reefs in low intertidal and shallow subtidal zones. Forms soft, velvety, dark green cushions and branching fronds that look like green velvet or soft sponge.
Range
Found throughout the North and South Islands on rocky shores in intertidal zone. Most common on exposed and semi-exposed coastlines. Also found in temperate regions worldwide.
Endemism
Introduced
Main Threats
None significant. This species is common and widespread on rocky shores. Localised threats include coastal development, pollution, and rock pool disturbance.
Population
Not Threatened. Sea velvet is common on rocky reefs throughout New Zealand, particularly in sheltered and semi-sheltered locations. It is native to New Zealand and Australia, but has been introduced to other parts of the world where it has become a problematic invasive species.
Conservation Status
Not Threatened
Human Risk
harmless
Handling Note
marine algae, safe to handle
Conservation Note
Introduced green algae; invasive in some areas, not subject to conservation assessment.
Te Ao Māori
No recorded Māori name distinguishes the sea velvet from other green seaweeds. It was likely grouped with other green seaweeds called rimu. The soft, velvety cushions would have been noticed. They looked like the velvet cloaks of chiefs. Like the soft moss of the forest floor. They were a reminder that the sea has its own textures. Its own softness. The sea velvet was sometimes used as a padding. The soft, spongy fronds were gathered and dried. Then used to line baskets or to cushion fragile items.
The water is calm. The rock is soft. Codium fragile grows. The soft one has fronds that are dark green. Soft. And velvety. Like green velvet or soft sponge. They are cylindrical. Branching. And finger-like. Often growing in dense, cushion-like clumps. The texture is soft and spongy. You can press it with your finger and feel it give. It looks comfortable. Inviting. Almost polite. It is the alga of the velvet surface. The one that is soft to the touch and easy to like. What makes it special is the invasion. The sea velvet is a model citizen in its native waters. But a troublemaker elsewhere. It has been introduced to Europe, North America, and South Africa. Probably in the ballast water of ships or attached to imported oysters. In those places, it spreads rapidly. Smothering native seaweeds and seagrasses. Changing the character of the reef. It is the polite one with bad habits. The one that is a friend at home and a bully abroad. The one that reminds us that context is everything. The sea velvet is a green alga. A member of the Codiaceae family. It is made of thousands of tiny, finger-like filaments. Packed together so densely that they form a solid, velvety mass. Each filament is a single cell. A long, thin tube with many nuclei. Under a microscope, the filaments are beautiful. A dense forest of green tubes packed tightly together. Biologically, the sea velvet reproduces by releasing spores from specialised structures on its fronds. It also reproduces by fragmentation. A piece broken off can grow into a whole new plant. This is why it spreads so easily. Why a single fragment can colonise a new reef. Why it is so hard to stop once it gets started. To find sea velvet is to find a soft, green cushion on the rock. It looks soft. Feels soft. Seems polite. But it is the one with bad habits. The one that causes trouble elsewhere. The one that proves that the most successful species are often the ones that are soft on the outside and tough on the inside. Not Threatened. Sea velvet is common on rocky reefs throughout New Zealand. Particularly in sheltered and semi-sheltered locations. It is native to New Zealand and Australia. But has been introduced to other parts of the world where it has become a problematic invasive species.