the iridescent red alga of NZ's subtidal rock faces

Size
Height: 5–15 cm
Lifespan
2–5 years
Diet
Grows on rocky reefs and in sheltered harbours in low intertidal and shallow subtidal zones. Requires clean water, stable rock surfaces, and good water flow. Tolerates shade, moderate wave action, and temperature fluctuations.
Habitat
Grows on rocky reefs and in sheltered harbours throughout New Zealand, from the Three Kings Islands down to Stewart Island. A creature of the low intertidal and shallow subtidal zones, the places where the light filters through the water and the rocks are covered in a garden of pink and red. A subtle show-off, shimmering beneath the surface like oil on glass.
Range
Found throughout the North and South Islands on rocky reefs and in sheltered harbours in low intertidal and shallow subtidal zones. Most common in clear, sheltered waters with good water flow. Also found in Australia and South America.
Endemism
Native
Main Threats
None significant. This species is common and widespread in clear, sheltered waters. Localised threats include coastal development, pollution, sedimentation from land clearance, and climate change affecting water temperature and clarity.
Population
Not Threatened. Iridescent red algae is common on rocky reefs throughout New Zealand, particularly in sheltered locations with clear water. It is often found growing on vertical rock faces and under overhangs, where the light is low but the water flow is steady.
Conservation Status
Not Threatened
The subtle show-off of the reef is, at first glance, a flat, brownish-red disc clinging to the rock. It is not flashy. It is not bright. It is almost drab. But then the light hits it at the right angle, and it shimmers, blue, green, purple, silver, like oil on a wet road. The iridescence comes from the structure of its cells, which reflect light in a way that creates a rainbow effect. It is the alga of the hidden shimmer, the one that waits for the right light to show off. What makes it special is the shimmer. The iridescence is not a pigment. It is a structural colour, created by the way the cell walls bend and reflect light. It is the same phenomenon that makes soap bubbles shimmer and peacock feathers glow. It is a trick of the light, a secret hidden in the cells, a magic trick that only works when the sun is at the right angle. It is the alga of the hidden beauty, the one that keeps its best trick for those who look closely. The fronds are flat and fan-shaped, often split into several broad lobes. They are tough and leathery, able to withstand the motion of the waves. The edges are wavy and ruffled, like a piece of crinkled paper. The surface is smooth and glossy, almost waxy to the touch. Under the water, the fronds are a deep reddish-brown, almost invisible against the rock. Biologically, the iridescent red algae is a red alga. It reproduces by releasing spores from specialised structures on its fronds. The spores are released into the water, carried by the currents, and settle on nearby rocks to grow into new plants. To see the iridescent red algae at its best, you have to dive beneath the surface. In the water, with the light filtering down, the iridescence is stunning. The fronds shimmer with blue and green, purple and silver. It is a subtle show-off, a quiet treasure, a flash of colour in the dim light. It is the alga of the patient eye, the one that rewards those who take the time to look, the one that proves that the most beautiful things are often hidden in plain sight.