sea felt forming dense velvety mats on sheltered intertidal rock
- Size
- Width: 5–15 cm
- Lifespan
- 3–7 years
- Diet
- Photosynthetic - grows on rocky shores in intertidal zone, forming dense, felt-like mats. Requires clean water, stable rock surfaces, and good light. Tolerates wave action and exposure to air at low tide.
- Habitat
- The sea felt grows on rocky reefs throughout New Zealand – from the Three Kings Islands down to Stewart Island, in the low intertidal and shallow subtidal zones. It is a creature of the shadows, the crevices, the places where the light is low and the water is still. It forms soft, velvety, felt-like mats on the rocks – dark green, spongy, and oddly comfortable-looking.
- Range
- New Zealand - found throughout the North and South Islands on rocky shores in intertidal zone. Most common on exposed and semi-exposed coastlines.
- Endemism
- Native
- Main Threats
- None significant - this species is common and widespread on rocky shores. Localised threats include coastal development, pollution, and rock pool disturbance. Classified as Not Threatened.
- Population
- Not Threatened. Sea felt is common on rocky reefs throughout New Zealand, particularly in shaded, sheltered locations. It often grows on vertical rock faces and under overhangs. It is not rare. It is just very, very felt-like.
- Conservation Status
- Not Threatened
The sea felt is the soft one. It does not have fronds or branches or leaves. It forms a thick, velvety mat on the rock, like a piece of green felt or a soft sponge. The texture is soft and spongy – you can press it with your finger and feel it give. It looks almost comfortable, like something you might want to lie down on.
What makes it special? The texture. The sea felt is made of thousands of tiny, finger-like filaments, packed together so densely that they form a solid mat. Each filament is a single cell – a long, thin tube with many nuclei. The filaments branch and intertwine, creating a spongy, felt-like structure. It is the velvet of the underwater world.
The sea felt is a green alga, a member of the Codiaceae family. It is not calcified like some other green algae. It is soft and flexible, able to absorb the energy of the waves without tearing.
Biologically, the sea felt reproduces by releasing spores from specialised structures on its filaments. The spores are released into the water, carried by the currents, and settle on nearby rocks to grow into new mats. It also reproduces by fragmentation – a piece broken off can grow into a new mat.
The sea felt provides habitat for small invertebrates. Tiny crustaceans hide among its filaments. Small snails graze on its surface. Its soft, spongy texture creates a damp, protected microclimate, a refuge for the small creatures of the reef.
To find sea felt is to find a soft, green mat on the rock. It looks like felt, feels like a sponge, sits there quietly in the shadows. You can press it with your finger and feel it give. It is the soft one, the velvety one, the one that looks oddly comfortable on the cold, hard rock.