cushion star spread across every shallow reef
- Size
- Length: 3–5 cm
- Lifespan
- 3–5 years
- Diet
- Herbivorous and grazing. Feeds on algae and small invertebrates. Grazes on encrusting organisms on rocks. A slow-moving, non-predatory sea star that uses tube feet to scrape food from surfaces.
- Habitat
- Rocky shores, intertidal zones, harbours, and estuaries from mid-tide mark down to 10 metres depth. Often found under rocks and in rock pools. Prefers areas with abundant algae and encrusting organisms.
- Range
- Found in coastal waters of North and South Islands from Northland to Stewart Island. Most common in intertidal zones and shallow harbours. Also found in Australia. Distribution follows suitable rocky habitats.
- Endemism
- Native
- Main Threats
- No significant conservation threats. Climate change affecting intertidal habitats and ocean acidification may impact larval development. Warming waters may shift distribution of suitable habitat significantly.
- Population
- Populations considered stable and widespread. Species is common in intertidal zones throughout New Zealand. No formal conservation assessment exists. Small size and camouflage make it easy to overlook. One of most frequently encountered sea stars in rock pools.
- Conservation Status
- Not Threatened
Pentagonal and plump, it looks more like a cushion than a starfish. The cushion star has very short arms. They are barely distinguishable from the central disc. Its body is thick and fleshy. It is covered in small spines that give it a velvety texture. The colour ranges from olive-green to brown to orange. Darker mottling is often present. Form follows function. Shape aids concealment. The texture is soft. The appearance is unassuming.
Under rocks and in rock pools, it hides during low tide. The cushion star is common in the intertidal zone. It must survive twice-daily exposure to air and sun. It wedges itself into damp crevices. It seals its body to retain moisture. When the tide returns, it emerges to feed. Survival depends on retention. Exposure leads to desiccation. The cycle is tidal. The response is instinctive.
Unlike many sea stars, it is not a predator. The cushion star grazes on algae and small encrusting animals. It scrapes food from the rock surface with its tube feet. It moves slowly. Deliberately. It leaves a trail of cleaned rock behind it. It is a browser. Not a hunter. Consumption is gentle. Impact is local. The rock stays clean. The algae grows back. Balance is maintained.
Small and well-camouflaged, it is easy to overlook. The cushion star blends with the rocks and algae of the intertidal zone. You can stare directly at a rock pool and see nothing but barnacles and seaweed. Only then do you realise that several cushion stars are hiding in plain sight. Their bodies match the background almost perfectly. Visibility is low. Detection is difficult. The eye misses. The creature remains.
Intertidal zones provide its preferred habitat. The cushion star lives from the mid-tide mark down to ten metres depth. It occurs on rocky shores, in harbours, and in estuaries. It is most common in areas with abundant algae. This is the same algae that provide its food. When the algae bloom, the cushion stars multiply. Resource availability drives population. Abundance follows supply. The link is direct.
Reproduction occurs in spring and summer. The cushion star releases eggs and sperm into the water. Fertilisation occurs there. The larvae drift in the plankton for several weeks. They settle to the bottom. They are tiny at first. Barely visible. But they grow quickly in the warm, food-rich waters of the intertidal zone. Growth is rapid. Survival is chance. The next generation arrives. The cycle continues.
Climate change may affect its intertidal habitat. Warming waters and rising sea levels will change the distribution of rocky shores. They will change the algae that grow on them. The cushion star is adaptable. But it has limits. For now, it remains a common sight in rock pools. A small, pentagonal, cushion-like presence in the space between tides. Adaptation is tested. Limits are unknown. The future is uncertain. The present is stable. No one told it otherwise. It carries on. The tide comes in. The tide goes out. The star grazes. The rock stays clean. It is a quiet victory. No fanfare accompanies it. No celebration marks it. The cushion star simply exists. It continues its work. It maintains its watch. And that seems to be enough.