looks like red plastic on the reef rocks
- Size
- Height: 10–30 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 of clear, sheltered waters. Forms broad, flat, red blades that look like red plastic.
- Range
- Found throughout the North and South Islands on rocky reefs in low intertidal and shallow subtidal zones of clear, sheltered waters. Most common in the North Island, particularly in northern harbours and bays. Introduced from Asia, now established in New Zealand waters.
- Endemism
- Introduced
- Main Threats
- None significant. This introduced species has become established in New Zealand waters. Localised threats include coastal development, pollution, and climate change affecting water temperature. Can form dense beds that may compete with native seaweeds.
- Population
- Not Threatened, but potentially problematic. Red blade algae is an introduced species that has become established in New Zealand waters, particularly in the North Island. It can form dense beds that may compete with native seaweeds.
- Conservation Status
- Not Threatened
- Human Risk
- harmless
- Handling Note
- marine algae, safe to handle
- Conservation Note
- Introduced red algae; invasive in some areas, not subject to conservation assessment.
- Te Ao Māori
- No recorded Māori name distinguishes the red blade algae from other red seaweeds. It is not a traditional seaweed of New Zealand. It arrived after the time of the ancestors. The red blade algae is a newcomer. A stranger washed up on the shore. It is a reminder that the sea is always changing. That new things arrive and old things fade. Today, the red blade algae still spreads along the coasts of New Zealand. You can see it at low tide. A flash of red on the rocks. It is beautiful and troubling. A sign of a changing world.
Without it, the reef is green. With it, there is red.
Grateloupia turuturu looks like it does not belong. It has blades that are broad, flat, and fleshy. Bright red to reddish-brown. Sometimes with a metallic sheen. They can grow up to 30 centimetres long and 10 centimetres wide. Looking like sheets of red plastic or oversized rose petals. It is a show-off. A stranger in a strange land. And it is spreading. It is the alga of the flashy colour. The one that catches your eye from across the pool. The one that is beautiful but troubling.
What makes it special is the colour. The red blade algae is a brilliant, vibrant red. The kind of red that catches your eye from across the pool. It stands out against the green and brown of the native seaweeds. A flash of tropical colour in the temperate water. It is beautiful. But it is also a warning. It is the alga of the warning colour. The one that says look at me. I am not from here. The one that is both a treasure and a threat.
The red blade algae is an introduced species. It came from Asia. Probably in the ballast water of ships or attached to imported oysters. It has spread along the coasts of the North Island. Forming dense beds that smother native seaweeds and change the character of the reef. It is not as aggressive as some invasive seaweeds. But it is spreading. It is the alga of the slow invasion. The one that is winning by being patient. Biologically, the red blade algae is a red alga. It reproduces by releasing spores from specialised structures on its blades. The spores are released into the water. Carried by the currents. And settle on nearby rocks to grow into new plants. It also reproduces by fragmentation. A piece broken off can grow into a new blade. To find red blade algae is to find a flash of red on the reef. It is beautiful. But it is not from here. It is the invasive one. The pushy one. The one that reminds us that the sea is connected. And that nothing stays in its place forever. The one that proves that beauty can be a warning.