five-armed giant of the mountain shallows

Size
Length: 10–12 cm
Lifespan
10–20 years
Diet
Carnivorous – fed on barnacles, molluscs, and other slow-moving invertebrates in high intertidal splash pools and exposed headlands. A starfish built for the cold – small, robust, with short, thick arms and mottled greenish-brown colour blending perfectly with the rock.
Habitat
High intertidal rocks, splash pools, and exposed headlands of the Otago peninsula down to Stewart Island and subantarctic islands. A starfish built for the cold – small, robust, with short, thick arms and mottled greenish-brown colour blending perfectly with the rock.
Range
Found on high intertidal rocks, splash pools, and exposed headlands of the Otago peninsula down to Stewart Island and subantarctic islands. Described from early naturalist accounts and preserved specimens. Last reliably recorded in the 1890s.
Endemism
Endemic
Main Threats
Coastal development and pollution were the primary threats. Also threatened by climate warming that affected water temperature, and rock pool disturbance from collectors and visitors. Last reliably recorded in the 1890s, gone by the 1910s.
Population
Described from early naturalist accounts and preserved specimens. Estimated arm span 10–12 centimetres – significantly larger than any living asterinid in New Zealand today. Its arms were thicker and its body was more robust than any living relative. Last reliably recorded in the 1890s, gone by the 1910s.
Conservation Status
Extinct
A starfish lives where the waves crash and the spray flies, where the sun bakes the rocks at low tide and the cold water rushes in at high tide. Not the large, eleven-armed stars of the deep reefs. Not the cushion stars of the sheltered bays. But a starfish with short, thick arms, a mottled greenish-brown colour, a body built to withstand the pounding of the southern ocean. That was the giant alpine sea star, and it was the rock pool phantom of the high shore. It lived in the high intertidal zone – the highest part of the shore, where the water covers the rocks for only a few hours each day. It had to survive long periods of exposure to the sun and the air, extreme temperatures, and the crashing of the waves. It was the most cold-tolerant starfish in New Zealand, adapted to the harsh conditions of the southern coast. It grazed. The giant alpine sea star fed on the film of algae and bacteria that grew on the rocks. It scraped the surface with its tiny tube feet, grazing like a cow on a pasture. It was a grazer, a cleaner, a keeper of the rock. Starfish reproduce by releasing eggs and sperm into the water. The larvae drift in the plankton for weeks before settling on a rock and growing into tiny stars. That strategy works when the water is cold and the current is stable. It fails when the water warms and the coast is disturbed. Coastal development and climate warming destroyed it. When Europeans arrived, they developed the coasts for housing, harbours, and roads. They built seawalls, laid paths, cleared rocks. The giant alpine sea star, which lived only in the high intertidal zone of specific rocky shores, lost its home. At the same time, the climate warmed. The cold, southern waters that it depended on began to heat up. It could not tolerate the warmer temperatures. Its range contracted southward, then disappeared. By the 1910s, it was gone. The last specimens were probably collected by a naturalist who had no idea he was holding the final individual. He preserved them in alcohol, labelled them, put them in a drawer. And the high shore fell silent. The smaller starfish survived. The common cushion star, the eleven-armed star, the spiny star – they are still present on our rocky shores. They are smaller, more adaptable, able to tolerate a wider range of temperatures. They are the survivors, the ones that kept their heads down. But the giant alpine sea star is extinct. A few specimens in a museum jar, a few fragments of its DNA, and the memory of a starfish that used to cling to the high rocks, a rock pool phantom on the edge of the sea. The rock pool phantom has faded. The high shore is not as wild as it used to be.