SYSTEMS | 01.25.19
The Unsung Reef
Australia’s corals may get all the headlines, but the country’s kelp-dominated temperate reefs are at least as important and imperiled. Now they're finally getting the restoration focus they deserve.
Kelp requires cool, nutrient-rich waters to thrive, so its response to warming seas usually isn’t rosy. Long-term exposure to higher temperatures weakens the seaweed, slows its growth rate, and impedes its ability to reproduce. When storms assail the compromised kelp, the long algal ropes are frequently ripped loose from the ocean floor. In addition to these direct impacts, ocean warming allows new herbivores, including tropical fish and urchins, to move into kelp forest terrain. In some cases—especially in areas where their natural predators have been fished or hunted too heavily—these invaders can clear-cut large expanses of kelp forest in a matter of months.
In October, a team of scientists led by Dr. Thomas Wernberg at the University of Western Australia published a study predicting the response to future climate scenarios for 15 of the most common kelp and other seaweed species across the Great Southern Reef, a 71,000-square-kilometer (27,413-square-mile) band of kelp-dominated Australian coastline that stretches from Brisbane around Tasmania to Kalbarri. “Even under the most optimistic scenario,” says Wernberg, “these species are predicted to lose between 30–100 percent of their current area to ocean warming by 2100.”
Here in Tasmania, where ocean warming is currently occurring about four times faster than the global average, the situation is already quite dire. While several species of kelp have been heavily impacted by warming waters along these coasts, giant kelp (Macrocystis pyrifera
) has been hit the hardest; over the past 75 years, the species has disappeared from 95 percent of its former range across eastern Tasmania.
For underwater photographer Justin Gilligan, who grew up just north of Sydney and learned to dive in the kelp-dominated ecosystems of the Great Southern Reef, giant kelp forests hold a special kind of magic. “You swim through these swaying forests of giant bean stalks, and because there’s such a large floating canopy on the surface of the water, the understory is actually quite open,” says Gilligan. “You can explore in 3D and get up into the fronds, and it’s this shadowy, moody, dark world that’s full of unusual creatures.”
Gilligan’s first experience in a giant kelp forest was a little more than a decade ago off the coast of Eaglehawk Neck in southern Tasmania. Back then, he says, there were several healthy giant kelp forests close to town, and commercial dive operator Mick Barron regularly took tourists out to see them. Today, those forests are all gone. To photograph giant kelp for this story, Gilligan had to travel to the southern tip of Tasmania and board a boat piloted by a commercial abalone diver. There, in waters too remote to support ecotourism, he found himself alone and enchanted in some of the last remaining giant kelp forests in Australia.
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Great Southern Reef
The Reef’s relative obscurity and underappreciation are likely due, at least in part, to the understated qualities of the organisms that define it: kelp and other seaweeds. This is the stuff that fouls propellers and public beaches, that twines around your limbs should you be hardy enough to swim in the frigid waters where it resides. Unlike their psychedelically hued coral neighbors to the north, most seaweeds—there are thousands of species—are green, and brown, and occasionally a bold, rusty red. Many of their cohabitants are dressed to match. Still, despite this modest appearance, discounting and undervaluing seaweeds and the complex and important ecosystems they support, would be—has been—a grave mistake.
While the physiological resemblance is notable, the functional similarities between seaweeds and plants are far more important. Like the trees in a rainforest, seaweeds are the foundation of their world, its ecosystem engineers, says Adriana Vergés, a marine ecologist at the University of New South Wales. “They support entire ecological communities,” she explains. “This includes hundreds of species that get shelter, food, and habitat from these seaweeds.”
To scientists like Vergés and Johnson, who have spent decades studying seaweeds and their decline, the value of these ecosystems is undeniable. Some of that value is certainly economic. But much of the Great Southern Reef’s inherent worth lies in the astounding diversity of species it supports. And much of that diversity is unique. According to the 2016 paper that argued for the Reef’s recognition and protection, between 30 and 60 percent of its species are found nowhere else on Earth. Geographic isolation—the same factor that gave rise to marsupial mammals—is partly responsible for the Great Southern Reef’s abundance of unique organisms, the authors wrote. But so, too, have the region’s geologic and climatic conditions—environmental factors that remained remarkably stable here for 50 million years prior to the Industrial Revolution.
New Section Title Text Block (use if final text includes section titles)Their work day began several hours before the sun came up. As thick, ocean-hugging sheets of cold mist crept over the docks in Tasmania’s Pirates Bay, Simon Wally and Shane Bloomfield donned raingear that hadn’t completely dried from the days before and loaded well-used gear onto the boat. The sky and water were both still inky when they set off to check the lobster traps they’d dropped the previous afternoon, and the choppy swell seemed designed to urge them back to shore. But when the sun finally rose, casting a warm glow on the rugged, pristinely forested cliffs that ring the bay, the scene quickly became less forbidding. “It’s a beautiful place to wake up,” says Gilligan.
While Pirates Bay is almost impossibly picturesque, both above the waterline and below, its depths are increasingly troubled. When Wally and Bloomfield began pulling up their lobster pots, they did find southern rock lobsters (Jasus edwardsii) huddled inside, although there were fewer than they used to expect, and the animals tended to be smaller. However, the traps also contained a few eastern rock lobsters (Sagmariasus verreauxi), a warm-water species that never used to venture into southern Tasmania. Their haul was a snapshot of a changing fishery.
A 2015 study by scientists at the University of Tasmania revealed that southern rock lobster larvae experience significantly higher settlement success and lower predation rates when they land in kelp forests than when they end up in a barren habitat. It’s no surprise then that Tasmania’s native lobsters have become less numerous as kelp forests have disappeared. And while warmer waters have allowed eastern rock lobsters to enter the region for the first time, this species also struggles in degraded habitat.
Unsurprisingly, the rock lobster fishery isn’t the only industry suffering in the face of ocean warming. Over the past few decades, southern Australia’s abalone fishery has been even more heavily impacted by climate change. When subjected to warmer-than-usual waters, black-lipped abalone (Haliotis rubra) have higher metabolic rates and lower energy stores than normal, which makes them less resilient to stress; an extended oceanic heat wave in 2015 and 2016 caused a mass mortality event that claimed many thousands of abalone along the south and southeastern Tasmanian coast. Moreover, as kelp forests have declined and kelp-eating urchins have proliferated, abalone have been hit with an additional climate-induced punch. Food is now harder for the shellfish to come by (since kelp is their go-to meal), and there’s suddenly much more competition for limited calories. It’s a competition that the abalone rarely win. Field-based experiments have demonstrated that when long-spined urchins (Centrostephanus rodgersii) move into a kelp forest, abalone flee, seeking shelter in crevices and crannies where their ability to feed is hampered.
Ling and others are currently testing and implementing a wide range of urchin-mitigation strategies in an attempt to avoid that unsettling outcome. Their efforts run the gamut from low-tech (engaging abalone and volunteer divers to remove urchins from kelp forests by hand, and developing a fishery for urchin roe) to high-tech (testing an underwater drone that can autonomously detect and destroy urchins). Ironically, the most promising tool in their arsenal may be a species that’s struggling alongside black-lipped abalone: the southern rock lobster. In Tasmania, large rock lobsters are the primary predators of long-spined sea urchins, and—where their populations are healthy—they can be highly effective kelp forest guards. Field studies have demonstrated that even after invasive urchins have arrived in an area, a robust population of rock lobsters can prevent barrens from ever forming. Scientists are now advocating for lower commercial and recreational catch limits for rock lobsters, and they’ve launched a captive rearing program designed to bolster the lobster population in eastern Tasmania.
Collectively, these efforts might give the last remaining giant kelp forests—and the valuable fisheries they support—a fighting chance at survival. But addressing the urchin challenge, daunting as that task may be, won’t be sufficient to support this struggling ecosystem. In addition to their efforts to protect still-standing kelp forest remnants, scientists are also working to develop strategies for restoring barren habitat in the face of ongoing climate change.
New Section Title Text Block (use if final text includes section titles)Four years ago, Craig Johnson and a group of colleagues from the University of Tasmania launched an ambitious effort to transplant healthy common kelp (Ecklonia radiata) onto more than a hectare (~2.5 acres) of barren seafloor between Maria Island and the eastern Tasmanian mainland, painstakingly anchoring 500 mature individuals onto 28 different patches of artificial reef. For the next 18 months, they monitored those patches, studying the growth and reproduction success of the kelp and documenting the presence of other organisms drawn to their handmade habitat. Their findings underscore the importance of kelp as an ecosystem engineer, and they offer important insights for any future, large-scale efforts to restore degraded kelp habitat.
Within six weeks, the team’s transplanted kelp patches were already crammed with a wide range of animals and other algae species. On monitoring dives, the scientists were often treated to remarkable wildlife sightings, like this interaction between a Maori octopus (Macroctopus maorum) and an army of spider crabs (Leptomithrax gaimardii). “It was very reminiscent of that movie line,” says Dr. Cayne Layton, a postdoctoral researcher who works with Johnson, “’If you build it, they will come.’”
While each of their transplant patches attracted a diverse cast of species, the test forests weren’t all equally successful when it came to supporting future generations of kelp. “One of the primary things we learned is that there is a critical minimum patch size and density that must exist for kelp patches to be self-sustaining,” says Layton. “Juvenile kelp struggle to survive where there is insufficient adult kelp—and we think this is because the adult kelp help to reduce environmental stress, such as high light and sedimentation.” To be feasible and effective, future kelp restoration efforts must be self-sustaining. Based on their work with common kelp, scientists now know at least some of what it will take to achieve that goal.
Like Layton and Johnson, Vergés learned that minimum restoration patch sizes were critical to her success, partly to help her transplants withstand grazing pressure from herbivores like urchins. Notably, she also learned how to increase crayweed reproduction rates to levels significantly higher than those on natural reefs. “We think one of the reasons why our restored crayweed sites have such spectacularly high rates of reproduction is related to the restoration process itself,” says Vergés. “The process of taking the seaweeds out of the water, keeping them dry for 1–2 hours, and then re-submerging them in the ocean is known to stimulate the release of eggs and sperm.”
In an effort to do just that, the University of Tasmania and the Climate Foundation launched a new initiative in November to identify and cultivate giant kelp individuals that are better adapted to a warming ocean. The team, which includes Johnson and Layton, plans to grow these “super kelp” specimens in 100-square-meter test plots, manually removing any urchins that move in to limit their damage. Within their plots, they’ll look for individuals that can withstand the region’s predicted future conditions.
The fact that 95 percent of eastern Tasmania’s giant kelp forests are already gone might make their efforts seem almost futile. But in the remaining 5 percent, the scientists see hope. “Peculiarly, that remaining 5 percent of individuals, which are scattered right along the coast as single kelp individuals or very occasionally in small patches, appear to be quite healthy,” says Layton. “And so we are optimistic that we can identify and culture warm-water-tolerant genotypes from these remnant giant kelp and use these as a foundation for effective and wide-scale restoration efforts.” While reversing climate change is the ultimate solution to much of the degradation these valuable ecosystems are experiencing, innovative restoration approaches might at least buy them—and us—valuable time.
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ABOUT THE Photographer
Justin Gilligan is a photojournalist and marine scientist who has taken photographs and conducted research on some of Australia's most remote coral reef locations, including Lord Howe, Cocos (Keeling), and Christmas Islands. Gilligan was the recipient of the 2017 Australian Geographic Nature Photographer of the Year, the 2016 Save Our Seas Foundation's Marine Conservation Photography Grant, and received awards in the 2017 and 2018 Wildlife Photographer of the Year competition.
ABOUT THE Author
Stephanie Stone is the Pam McCosker Director of Science Communication at the California Academy of Sciences andbioGraphic
’s Editorial Director. She oversees the magazine’s content strategy and development, as well as strategic distribution partnerships. With a degree in anthropology from Harvard University, Stone has spent the vast majority of her career developing effective ways to share information about science and nature with public audiences. In addition to finding and helping to craft compelling stories forbioGraphic
, she has written about science and the environment forSierra Magazine, California Wild
, and theSan Francisco Chronicle
, and has lectured on science communication at Stanford University. Follow her on twitter @StephStoneSF.
Justin Gilligan Stephanie Stone
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