There are few places in the world where you can dive among giant kelp forests like those that used to flourish along the Tasmanian east coast.

Growing up to 40 metres from the ocean floor, the forests protected a vibrant ecosystem of sponge garden, fur seals, crayfish, weedy sea dragons and countless fish species.

Mick Baron, a dive instructor and trained biologist, has watched them disappear.

The forests started to die in the north of Tasmania in the 1960s. Baron first noticed them vanishing from Deep Glen Bay, a short boat ride north-east of his dive centre at Eaglehawk Neck, in the late 1990s.

The sea along the Tasmanian east coast is a global heating hotspot. Temperatures there have risen at nearly four times the global average.

They are about 2C hotter than a little over a century ago.

Warm water pushed down the coast by the east Australian current has stripped the area of nutrients, brought new marine species, and killed more than 95% of the giant kelp. The impact on local ecosystems and fisheries has been severe.

“Our whole ocean has effectively shifted to the south,” Baron says.