The Great Barrier Reef isn’t Australia’s only underwater environment to suffer as a result of global warming. The Great Southern Reef is quietly slipping toward destruction with little fanfare. Stretching from just below Brisbane on the east coast to Kalbarri on the west coast, this life-giving ecosystem is made up of rocky, temperate reefs and characterized by once-vast forests of giant kelp. Today, Tasmanian kelp forests are on the brink of disappearing forever. This island state to the south of mainland Australia was particularly well-known for its rich submarine jungles. But early in October, well-known Tasmanian dive operator Mick Baron reported that the last patch of kelp on the island’s east coast was gone. Baron, who runs Tasmania’s Eaglehawk Dive Center, went to Munro Bight searching for the patch, only to find that a recent storm had ripped from its roots.
Will the Tasmanian kelp forests disappear forever?
Tasmania has lost 95 percent of its giant kelp forests over the last 80 years because of global warming. Patches on the island’s east coast may one day grow back, but it is far more likely that the disappearance of the Munro Bight patch means the end of an ecosystem that has inhabited Tasmania’s east coast for tens of thousands of years. According to Dr. Thomas Wernberg from the University of Western Australia’s Oceans Institute, losing the Great Southern Reef would be as catastrophic as losing the Great Barrier Reef.
Why is this happening?
When Baron first started diving on Tasmania’s east coast almost 45 years ago, he could not navigate the thick kelp forests by boat. Now, even though the plant can grow up to two feet (60 cm) per day, those forests are a thing of the past. Rapidly rising sea temperatures, caused by Tasmania’s unique geographical location, are to blame.
Historically the warm East Australian Current moved southward along the Australian mainland, then veered eastward long before reaching Tasmania. But global changes have altered the current’s course, and its warm, nitrogen-deficient waters now veer ever-closer to Tasmania. As a result, sea temperatures around the island are increasing up to three times faster than the global average. Such rapid changes mean the cool-water kelp cannot possibly successfully adapt in time.
In the past, when winter storms ripped the last of the summer season’s kelp from the seafloor, its exceptional growth rate allowed it to quickly regenerate. Now, stressed by increased temperatures and starved of the nitrogen it needs to grow, the kelp cannot recover. To make matters worse, higher water temperatures have created optimum conditions for the long-spined sea urchin. This invasive species preys on new kelp shoots. Overfishing compounds the problem by removing populations of rock lobster, the sea urchins’ natural predator. As a result, depleted kelp beds have become lifeless deserts, grazed into extinction by the urchins.
What’s next?
If the kelp forests of the Great Southern Reef disappear, the world will lose more than just the plants themselves. The kelp ecosystem supports a huge variety of marine life, including several endemic species. Scientists estimate that 30 percent of the Great Southern Reef’s fish species are endemic (including the iconic weedy seadragon). Up to 80 percent of its seaweed species are exclusive to that area as well. Many Australian fisheries depend on the health of this unique ecosystem, which generates approximately $10 billion every year.
Unfortunately, the future looks grim for the remaining Tasmanian kelp forests on the island’s other coasts. Kelp forests elsewhere on the Great Southern Reef are in similar dire straits. The East Australian Current hasn’t rounded Tasmania’s most southerly point yet, but if global warming continues unchecked, it is only a matter of time. Dr. Wernberg’s model predicts that giant kelp may be extinct in Australia by the end of the century.
