Andrea Wild, CSIRO( andrea. wild @ csiro. au)

Tasmania was once surrounded by majestic forests where sea creatures lived in the quiet beauty among towering tangles of Giant Kelp. But as our climate changes, the seas around Tasmania have warmed and the East Australian Current has flowed further south. This has brought nutrient-poor waters and invading sea urchins to Tasmania.

Warm waters, low nutrients and sea urchins are deadly to Giant Kelp. In recent decades, the once widespread forests of Giant Kelp around Tasmania have declined by 95 per cent. Giant Kelp Forest is now listed as an endangered marine community type.

A giant among seaweeds

Giant Kelp( Macrocystis pyrifera) is a species of seaweed, or macroalgae. It grows in cold, shallow seas around the world, from California to New Zealand. Giant Kelp individuals can reach well over 50 metres tall.

In the shallow seas around Tasmania, Giant Kelp grows to around 30 metres tall. At its base, Giant Kelp has a holdfast to attach to rocks or hard substrate on the sea floor. Long stems, called stipes, grow toward the surface. Leaf-like blades grow along the stipes, with gas bladders at their base to help them float. On the surface of the sea, blades of giant kelp fold and bathe in the sun and sea spray. and surface in its canopy. A network of insects, like kelp flies, recycle Giant Kelp that has detached and washed ashore at the end of its life. Without Giant Kelp to form the forests, the entire ecosystem disappears.

Climate change threatens the few remaining strongholds of Giant Kelp in Tasmania. Warming in the Tasman Sea is twice the global average. Giant Kelp is very sensitive to warmer water temperatures.

Tasmania’ s shallow seas are the last stop before Antarctica. There is nowhere for Giant Kelp to retreat. But there is hope. We are working with partner organisations to restore Tasmania’ s giant kelp forests. By breeding giant kelp that is tolerant of warmer water and replanting it in the ocean, we hope to bring back the entire marine community.

Growing giants in the lab

Giant Kelp is huge, but in our laboratory we mostly work with Giant Kelp gametophytes. They are the microscopic stage in the life cycle of Giant Kelp.

When Giant Kelp reach around five metres tall, they begin releasing microscopic spores from special blades at their base, which are called sporophylls.

Illustration by Rachel Tribout

Giant Kelp at Tinderbox Marine Reserve. Credit: Andrew Wilson

No forest without trees

Giant Kelp in the sea are like trees on land. But unlike forests on land, there is only one species creating the forest: Giant Kelp. The other species in the forest depend on it entirely. The young of many fish species shelter here in nurseries. Octopuses, sea stars and jellyfish carry out their lives. Marine plants and seaweeds grow in niches in the forest. Sea lions weave through the forest

Illustration by Rachel Tribout

Spores settle on the sea floor where they mature into microscopic female or male gametophytes and produce eggs or