sheets up on the high tide rocky shores

Size
Length: 10–25 cm
Lifespan
1–2 years
Diet
Photosynthetic. Draws energy from sunlight and nutrients from surrounding water. Requires clean water and good flow.
Habitat
Grows on rocky shores in high and mid intertidal zone. Forms thin, red, crumpled sheet-like fronds that tear easily but grow back quickly.
Range
Found throughout the North and South Islands on rocky shores in high and mid intertidal zone. Most common on exposed and semi-exposed coastlines. Also found in Australia and South America.
Endemism
Native
Main Threats
None significant. This species is common and widespread on rocky shores. Localised threats include coastal development, pollution, rock pool disturbance, and climate change affecting intertidal conditions.
Population
Not Threatened. Red sheet algae is common on rocky shores throughout New Zealand, particularly in the upper intertidal zone. It is often found growing on rocks in the splash zone, where it is exposed to the air for long periods at low tide.
Conservation Status
Not Threatened
Human Risk
harmless
Handling Note
marine algae, edible species safe to handle
Conservation Note
Native red algae; not assessed by NZTCS as marine algae are outside the scope of current threat classifications.
Te Ao Māori
No recorded Māori name distinguishes the red sheet algae from other red seaweeds. It was likely grouped with other red seaweeds called karengo. The thin, red sheets would have been noticed. They looked like the skin of a fish. Like the membrane of an egg. Like something fragile and precious. They were a reminder that the sea has its own delicacy. Its own fragility. The red sheet algae was sometimes used as a food. The thin, papery fronds were gathered. Dried. And eaten as a snack or used as a seasoning.
It tears easily. But it never gives up. Pyropia cinnamomea is the thin one. It has fronds that are flat, thin, and sheet-like. Often crumpled or ruffled. Like red tissue paper or cellophane. They are a deep reddish-purple to brownish-red. Sometimes with a metallic sheen. They are only one or two cells thick in places. So thin that you can see through them. They tear easily. A gentle tug will rip the frond. But they grow back quickly. Regenerating from the smallest fragment. It is the alga of the fragile strength. The one that tears but never gives up. What makes it special is the resilience. The red sheet algae lives in the harsh upper intertidal zone. Where it is exposed to the sun and the air for hours at a time. Its fronds dry out. Shrivels. And seem to die. But when the tide returns, they rehydrate within minutes. Turning soft and pliable again. It is the resurrection plant of the sea. The one that comes back from the dead every day. The one that has learned to survive the harshest conditions. The red sheet algae is a red alga. A close relative of the seaweed used to make nori for sushi. In fact, some species of Pyropia are cultivated for nori in Japan and Korea. Our New Zealand species is not as widely used. But it is edible. The thin, papery fronds can be dried and eaten as a snack. Or used as a seasoning. Biologically, the red sheet algae reproduces by releasing spores from specialised structures on its fronds. The spores are produced in dark patches on the surface of the sheet. The spores are released into the water. Carried by the currents. And settle on nearby rocks to grow into new plants. To find red sheet algae is to find a crumpled red sheet on the rock. It is thin. Fragile. Easily torn. But it is also resilient. Coming back every day. Surviving in the harsh splash zone. It is the thin one. The sheet-like one. The one that tears easily but grows back anyway. The one that proves that fragility and resilience can coexist. Not Threatened. Red sheet algae is common on rocky shores throughout New Zealand. Particularly in the upper intertidal zone. It is often found growing on rocks in the splash zone. Where it is exposed to the air for long periods at low tide.