the branching red alga of NZ's subtidal reef edges
- Size
- Height: 5–15 cm
- Lifespan
- 1–3 years
- Diet
- Grows on rocky reefs in clear, sheltered waters of low intertidal and shallow subtidal zones. Requires clean water, stable rock surfaces, and good water flow. Prefers vertical rock faces and under overhangs where protected from full wave force.
- Habitat
- Grows on rocky reefs throughout New Zealand, from the Three Kings Islands down to Stewart Island, in the low intertidal and shallow subtidal zones. A creature of the clear water, the sun-dappled reefs, the places where the light filters through and the current flows gently. Forms intricate, branching fronds that look almost ornamental, like a hand-crafted decoration or a piece of delicate coral. The ornamental one, the delicate one, the one that looks hand-crafted.
- Range
- Found throughout the North and South Islands on rocky reefs in clear, sheltered waters. Most common in low intertidal and shallow subtidal zones. Also found in temperate seas worldwide, so not endemic. Grows on vertical rock faces and under overhangs where protected from wave action.
- Endemism
- Native
- Main Threats
- None significant. This species is common and widespread on rocky reefs. Localised threats include coastal development, pollution, sedimentation from land clearance, and climate change affecting water temperature and clarity.
- Population
- Not Threatened. Branching red algae is common on rocky reefs throughout New Zealand, particularly in clear, sheltered waters. It often grows on vertical rock faces and under overhangs, where it is protected from the full force of the waves.
- Conservation Status
- Not Threatened
The ornamental one has fronds that are flattened and branching, dividing again and again into smaller and smaller segments. The branches are arranged in a regular, repeating pattern, a fractal of pink and red. It looks like a tiny tree or a piece of coral. It looks hand-crafted, as if someone spent hours arranging each branch just so, a living sculpture on the rock.
What makes it special is the intricacy. The branching pattern of Plocamium is distinctive and beautiful. The main axis is flattened, with branches arranged in opposite pairs or in a comb-like pattern. The tips of the branches are often curved, like tiny hooks. The whole plant is stiff and cartilaginous, you can bend it, but it will not break easily. It is the alga of the intricate pattern, the one that looks like it was designed by a jeweller.
The colour is a beautiful pinkish-red, sometimes with purple or orange highlights. It is a subtle colour, not flashy, but rich and warm. It stands out against the dark rock, a flash of pink in the green and brown of the reef. Under the water, the colour is even more vibrant, the sunlight filtering through the fronds and illuminating the pink tissue.
Biologically, the branching 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. It also reproduces asexually, fragments breaking off and growing elsewhere.
To find branching red algae is to find a piece of living jewellery on the reef. The pinkish-red fronds stand out against the dark rock, their intricate branches catching the light. It is delicate, beautiful, almost fragile. But it is tougher than it looks, holding on to the rock, swaying in the current. It is the ornamental one, the delicate one, the one that proves that small things can be just as stunning as the giants, that the underwater world is full of beauty if you take the time to look.