the bull kelp anchoring NZ's exposed rocky shores
- Size
- Length: 50–150 cm
- Lifespan
- 2–5 years
- Diet
- Photosynthetic. Absorbs dissolved nutrients from cold, moving seawater. Requires strong water movement and stable rock attachment.
- Habitat
- Grows on exposed rocky reefs throughout southern New Zealand, from Cook Strait down to Stewart Island and the subantarctic islands. A creature of the rough water, the wave-battered coast, the places where the current never stops. Forms long, strap-like, corrugated blades that look like brown leather belts or strips of corrugated cardboard.
- Range
- Found on exposed rocky reefs in southern New Zealand from Cook Strait down to Stewart Island and the subantarctic islands. Most common in rough, cold water of the South Island and Stewart Island. Also found in Australia and Chile.
- Endemism
- Endemic
- Main Threats
- None significant. This species is common on exposed rocky reefs in southern New Zealand. Localised threats include coastal development, pollution, sedimentation from land clearance, and climate change affecting water temperature.
- Population
- Not Threatened. Brown strap kelp is common on exposed rocky reefs in southern New Zealand, particularly in the South Island and Stewart Island. It often forms dense beds in the shallow subtidal zone, in the same rough-water habitats as other Lessonia species.
- Conservation Status
- Not Threatened
- Human Risk
- harmless
- Handling Note
- marine algae, safe to handle
- Conservation Note
- Endemic brown 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 brown strap kelp from other brown seaweeds. It was likely grouped with other brown seaweeds called rimu. The corrugated blades would have been noticed. They looked like the belts worn by warriors. Like the armour of the sea. They were a reminder that the sea has its own toughness. Its own way of protecting itself. The brown strap kelp was sometimes used as a strap. The tough, leathery blades were dried and used to tie bundles or to secure loads.
Waves define its shape. The tough one has blades that are long, narrow, and strap-like. Up to 2 metres long and 10 centimetres wide. They are corrugated. With a wavy, ridged surface that looks like corrugated cardboard or a piece of flexible armour. The colour is dark golden-brown to olive-green. The blades are thick and leathery. Tough and strong. Able to withstand the constant pounding of the waves. It is the alga of the rough water. The one that bends but does not break.
What makes it special is the corrugation. The wavy, ridged surface of the blade is not just for show. It gives the blade extra strength. Allowing it to bend and flex without tearing. It is like the corrugation in cardboard. A simple trick that turns a flat sheet into a strong, rigid structure. The brown strap kelp is the flexible armour of the rocky shore. The one that has learned to go with the flow while still standing firm.
The brown strap kelp has a tough, woody holdfast. It anchors it firmly to the rock. From this holdfast, several thick, branching stipes (stems) rise toward the surface. Each stipe is covered in corrugated blades. Giving the plant a bushy, almost tree-like appearance. In the water, the blades stream out in the current. A golden-brown banner waving in the surge.
Biologically, the brown strap kelp is a brown alga. It reproduces by releasing spores from specialised structures on its blades. The spores are produced in dark patches on the surface of the blade. Visible as spots on the corrugated surface.
To find brown strap kelp is to find the corrugated blades on the exposed shore. They bend in the current. Flex in the waves. But they do not break. You can touch them. Feel the ridges. The toughness. The strength. It is the tough one. The corrugated one. The one built like flexible armour. The one that proves that flexibility is a form of strength.