kelp forest cathedral, now collapsed

Size
Height: 4000–5000 cm
Lifespan
3–7 years
Diet
Photosynthetic – absorbed nutrients from cold coastal waters through broad fronds. A kelp built for the deep – tall, thick-stemmed, with fronds reaching for light through the green gloom. The redwood of the sea, a forest of golden-brown columns swaying in the current, home to fish and crayfish and a thousand hidden creatures.
Habitat
Cold coastal waters of the South Island's west coast, Stewart Island, and subantarctic islands. A kelp built for the deep – tall, thick-stemmed, with fronds reaching for light through the green gloom. The redwood of the sea, a forest of golden-brown columns swaying in the current.
Range
Found in cold coastal waters of the South Island's west coast, Stewart Island, and subantarctic islands. Subfossil remains found in coastal deposits. Last reliably recorded in the 1880s.
Endemism
Endemic
Main Threats
Ocean warming was the primary threat, along with overharvesting for the kelp industry. Also threatened by the loss of cold currents that sustained it. Last reliably recorded in the 1880s. A few fragments remain in museum collections – their golden-brown colour faded to grey, their underwater forests silent.
Population
An extinct New Zealand form of the genus Macrocystis, which includes the living giant kelp found in cold oceans worldwide. Estimated height 40–50 metres – taller than any living Macrocystis. Last reliably recorded in the 1880s, gone by the 1910s.
Conservation Status
Extinct
The giant bladder kelp washes up on southern beaches after a storm – long, hollow stipes, golden-brown fronds, bulbous floats that pop when you step on them. It is the great seaweed of the cold oceans, forming underwater forests that rival the tallest trees on land. New Zealand once had its own giant form of this kelp – taller, thicker, more massive than any living Macrocystis. Its fronds reached 50 metres towards the surface, its holdfast gripped the rocky bottom like a fist, its canopy shaded the seafloor. It was the underwater forest ghost, and it is gone. Size and its role in the sea made it special. A 50-metre kelp is a spectacular organism – not a plant but a brown alga, a distant relative of the seaweeds that wash up on the shore. It grows from the seafloor towards the surface, buoyed by gas-filled floats. Its fronds form a dense canopy that shades the water below. It is the engineer of the kelp forest ecosystem. It built the reef. A healthy kelp forest is a city of marine life. Fish shelter in the fronds. Crayfish hide among the holdfasts. Sea urchins graze on the kelp itself, and sea otters (once present, now gone) eat the urchins. The kelp provides food, shelter, and oxygen. It is the foundation of the coastal ecosystem. The giant New Zealand form would have been the redwood of this underwater forest – a towering column of life, its canopy so dense that the seafloor beneath was plunged into perpetual dusk. Kelp reproduces by spores, released from specialised structures on the fronds. The spores drift in the current, settle on the rocky bottom, and grow into tiny microscopic stages that then produce the next generation of giant kelp. That strategy works when the water is cold and the currents are stable. It fails when the ocean warms. Ocean warming and overharvesting destroyed it. The giant kelp was adapted to the cold, nutrient-rich currents of the southern oceans. As the climate warmed at the end of the last ice age, the range of the giant kelp contracted. The warm waters of the north were uninhabitable. It retreated south, then further south – and then there was no further south to go. At the same time, humans harvested kelp on an industrial scale. In the late 19th century, kelp was burned to produce soda ash and iodine. The giant kelp, with its massive stipes and dense beds, was a prime target. Harvesters cut the kelp from boats, pulling it from the rocky bottom, stripping the forests bare. The combination of warming and harvesting was fatal. The kelp could not regrow quickly enough. Its spore supply was depleted. Its holdfasts were torn away. By the 1910s, the giant New Zealand form was gone. The living Macrocystis still grows in the cold waters around the subantarctic islands and the far south – smaller, less robust, but alive. It is a survivor, a ghost of what used to tower off the mainland coast. But the giant coastal kelp is extinct. A few fragments in a museum drawer, a few holdfasts in coastal deposits, and the memory of a forest that used to sway beneath the waves. The ocean warmed. We harvested the forest. Then we wondered why the coast felt so empty.