Giant Underwater Forests Almost Gone!

The spectacular kelp forests, the giants of the deep sea off Tasmania’s East Coast have almost disappeared. What has happened to this unique environment and why didn’t we save them? Like our terrestrial high conservation forests we failed to act until the 21st century. In the meantime our underwater forests were far less visible, and before we knew it the last giant kelp stand was gone!

It is one of Australia’s most unique marine ecosystems, and a must-see spectacle for many divers.

Kelp forests were once widespread along the 250 kilometre east coastline of Tasmania where they thrived in cool waters, rich in nitrogen-filled nutrients. Some species such as the giant kelp Macrocystis pyrifera, the world’s largest seaweed, grew up to 45 metres in the deeper reaches of the southeast. Most notable was the grand kelp stands in Munro Bight on the Tasman Peninsula.

Over the past few decades the East Coast’s kelp forests have been on a rapid decline, and by the turn of this century they were down to the last few per cent of its original distribution. In the summer of 2015-16 there was essentially an underwater heat wave comprising well above average sea temperatures around Tasmania, and subsequently by winter the kelp forests were finally destroyed through a combination of warm water stress, and heavy storms.

The decline of an abundant ecosystem

The Australian arm of the huge gyre that moves water around the Pacific is the East Australian Current, which traditionally pushes warm water south along the coast of the mainland before turning east toward South America.

In recent decades with warming global climate this once-reliable system has altered, and now huge eddies of hot, nutrient-poor water keep spinning down toward the Tasmanian coast. Because of this, eastern Tasmania has some of the fastest warming ocean water on earth, which is more than twice the global average.

The 3 main factors that have caused the dramatic decline of kelp forests over the last half-century are –

• Sea temperature rises as a result of the global warming trend, have been too rapid for the Kelp forests to adjust. The warmer water being fed from the north also has low nutrient and nitrogen poor water.

• The Long-spined Sea Urchin eats the kelp roots where it anchors to the rock on the sea-bed. The warming seas are now warm enough to support the spawning of this urchin, and the increasing infestation of the East Coast water are having a dramatic effect on kelp.

• The overfishing of the Lobster, which predates upon the invasive Sea Urchin has resulted in the increased numbers of the Sea Urchin. This has allowed the urchins to establish themselves in plague proportions.

Thomas Wernberg from the University of Western Australia is modelling the giant kelp’s future, and his initial results suggest the warming climate will eliminate all giant kelp from Australia by the end of the century. Mr Werberg claims “ it’s big and charismatic and probably doomed for extinction”.

Craig Johnson, associate director of the Institute for Marine and Antarctic Studies in Tasmania agrees with Wernberg’s rough timeframe. “The crash brings an end to an ecosystem that has dominated Tasmania’s East Coast for tens of thousands of years.

It’s been the iconic shallow water rocky reef ecosystem. They are phenomenal places, both from a scientific and aesthetic point of view,” he says.

These kelp forests underpin the rich aquatic life around the Tasman Peninsula

In 2012, giant kelp forests were listed as an endangered ecological community by Australia’s government, the first marine community to be considered as such. The plight of Tasmania’s kelp forests has received little attention compared to the tropical coral reefs, but temperate marine ecosystems are just as important and encompass significant biodiversity, encompassing a multitude of fish, algae and crustaceans.

The giant kelp has the promising ability to recover very quickly given its prodigious growth rates. However the stress factors from warmer waters, nutrient starved low-nitrogen levels and increased predation from sea urchins looks to stifle a vigorous return to its former distribution.

Scientists of course saw this demise coming a long time ago. Though just like the ongoing CO2 emission debate, governments are forever burying their heads in the sand.

In 2010, I complied a World Heritage Area proposal for the Tasman Peninsula that encompassed a marine/terrestrial concept. The kelp forests were an imperative component of that proposal as they fulfilled the IUCN criteria or natural heritage listing in many respects.

The WHA proposal was handed directly the Tasmanian Greens, but it seemingly ended up in their trash can, as there was never a response.

• Bob Diver in Comments: I am thinking that the shocking decline of the commercial abalone fishery in Tasmania could somehow be linked to the seaweed problems. This decline is not spoken about very much, but it is rather scary (financially) and mentally hard work for those involved in trying to find abalone. You would be staggered to see the crappy catches from the east and west coasts today, compared to just five years ago, let alone ten years back. Last year saw the coldest seawater “ever” and this year is normal cold. I reckon it is something other than just water temperature causing the problems.