holds tight in the cook strait waves
- Size
- Shell: 6–10 cm, Weight: 20–40 g
- Lifespan
- 10–15 years
- Diet
- Phytoplankton and organic particles. Filters food from the water using its gills. Draws water in through its siphon and extracts microscopic algae. Feeds continuously when submerged.
- Habitat
- Rocky shores and intertidal zones from the low tide mark down to 20 metres depth. Attaches to rocks using strong byssus threads. Prefers areas with strong wave action and clear, clean water. Often found in dense beds on exposed coasts.
- Range
- Coastal waters of the North and South Islands from Northland to Stewart Island. Most common on exposed rocky shores and in Cook Strait. Also found in southern Australia and South America.
- Endemism
- Endemic
- Main Threats
- Recreational harvesting in some areas. Habitat loss from coastal development. Climate change affecting near-shore habitats and ocean acidification. No significant commercial fishery for this species.
- Population
- Populations are considered stable across most of the species' range. The ribbed mussel is not commercially harvested in New Zealand but is sometimes collected by recreational gatherers. Its strong, ribbed shell protects it from waves and predators.
- Conservation Status
- Not Threatened
- Human Risk
- harmless
- Handling Note
- commercially harvested mussel, rough shells may cause minor abrasions
- Conservation Note
- Endemic mollusc; commercially harvested and managed under the Quota Management System rather than NZTCS.
- Te Ao Māori
- In Māori tradition, Kopakopa was a mussel of the exposed rocky shores. Its strong, ribbed shell was noted for its toughness. It was gathered for food but was less favoured than the larger blue mussel or greenshell mussel because its flesh is smaller and tougher. The name Kopakopa describes the rough texture of the shell, a tactile reminder of the harsh environment in which it lives. It was a food of necessity, not of choice, but it sustained those who lived near the exposed coasts.
Named for the strong, radiating ribs on its shell, this mussel is built for survival. The ribs are not just decorative. They strengthen the shell, allowing it to survive in the rough, wave-beaten conditions of exposed rocky shores. A smooth-shelled mussel would be shattered by the pounding of the surf. The ribbed mussel's shell is engineered to withstand forces that would destroy a weaker shell.
It attaches to rocks using strong byssus threads that are thicker and stronger than those of the blue mussel. These threads are produced by a gland in the mussel's foot. The mussel extends its foot, touches it to the rock, and deposits a drop of liquid protein that hardens into a thread. The process takes seconds. A single mussel can produce dozens of threads, anchoring itself firmly to the rock.
The Maori name Kopakopa means rough or ribbed, referring to the texture of its shell. It is often found growing alongside barnacles and other hardy intertidal animals that can survive the pounding of the waves. Together, they form a dense mat of life on the exposed shore, each animal clinging to the rock with its own specialised attachment.
The ribbed mussel is not as large as the greenshell mussel, and its flesh is smaller and tougher. It is not commercially farmed, and it is rarely sold in fish markets. But it is a favourite of recreational gatherers who are willing to brave the waves to collect it. The effort is rewarded with a mussel that has an intense, briny flavour, concentrated by the harsh conditions of its home.
The ribbed mussel plays an important role in the ecosystem of the exposed rocky shore. Its dense beds provide habitat for small fish, crabs, and worms. The mussels filter the water, removing plankton and improving water clarity. They are the engineers of the wave-beaten coast, creating order in a place of chaos.