The effect of warmer waters on Australia’s Great Barrier Reef is cause for serious concern and may be an ominous sign of what’s in store for the world’s oceans as global temperatures rise. But running along Australia’s southern coast is a lesser-known wonder: the Great Southern Reef. Spanning hundreds of miles between Australia and Antarctica, it is a diverse ecosystem defined by some of the richest kelp forests in the world. But those grand marine forests down under are in big trouble:
Over the next few years, La Niña kept temperatures high as Wernberg and his colleagues conducted a detailed ecological survey of the Great Southern Reef. Overall, the two year heat wave triggered kelp forest die-backs across 2,300 square kilometers of reef and “functional extinction” along the northernmost 100 kilometers. Rather than recovering after the ocean cooled off, this dead kelp forest was replaced with seaweed mats and an odd assortment of invasive subtropical species.
It’s the most rapid and catastrophic kelp forest die-off ever seen anywhere on Earth.
Marine, grassland, and forest habitats are under threat from climate change worldwide. But they are especially vulnerable nearer the poles. Just as the Arctic has seen dramatic temperature spikes, almost certainly caused by a process climatologists call polar amplification, this southern region has now experienced temperatures well above average for several years and the effects are devastating.
Kelp forests perform much the same role in coastal seas as rain forests or polar forests do on land. They offer shelter and sustenance for a huge variety of organisms, many found nowhere else. The most prodigious species are the giant kelps, often found in stands reaching over 50 meters (160 feet) tall.
Because of the biodiversity they offer, kelp forests have served as important reservoirs of food and raw materials used by hunter-gatherers foraging alone the shore. There’s even a theory that back during the Pleistocene, large migrant communities worked well out to sea along the extended, ragged edge of seasonal ice in the Pacific and Atlantic oceans.
It’s even within the realm of possibility that Neolithic humans may have followed these forests almost all the way across the oceans, coming closer and closer to the New World, millennia before the American continents were colonized by paleo-Indian cultures 12,000 years ago or later Europeans during the Age of Discovery in the 15th and 16th centuries. If so we will probably never know: any telling remains would have been submerged under hundreds of feet of seawater and long since buried by marine deposits after the last ice age ended.
Like rain forests, kelp stands harbor hundreds of species found nowhere else on Earth. Unique brachiopods, aquatic insects, mollusks, colorful fish and squid are commonly seen swimming or crawling through the tangled, underwater maze. Even after a particular kelp dies and becomes detached from the sea floor, its gas-filled floats will often keep it on the surface for weeks. Schools of young fish and other small animals in otherwise open water form around and depend on these floating nurseries to hide from seabirds above and hungry predators below them.
But kelp are physically fragile, they need lots of deep ocean nutrients and circulating water to thrive. They are temperature sensitive in much the same way coral reefs are. Changes in ocean acidity, stagnant water, storms, and invasive species brought on by climate change are harming these ancient underwater gardens all over the world. Australian reefs, and the amazing ecosystems they support, seem to be taking the brunt of that onslaught.
The Great Southern Reef may not be as famous as the Great Barrier Reef. But it is critical to Australia’s commercial and sport fishing industries. It is a once in a lifetime destination for scuba divers and a living laboratory for researchers. All told, it brings in an estimated $10 billion a year to local economies. But the polar amplification process is now feeding back so viciously that there may be no stopping it now, at least in some places, including the southern coast of Australia.