In the 1980s, beaches in the Australian city of Sydney were frequently closed to swimmers because masses of poorly treated sewage were allowed to pour straight into the sea. Below the waterline, the pollution killed off dense stands of a jagged seaweed known as crayweed,k although the disappearance went unnoticed until much later. In 2007, a team of diving scientists surveyed the coastline and found dense crayweed canopies were common on the rocky reefs of New South Wales. But along more than forty miles of Sydney’s metropolitan coastline, they didn’t find a single seaweed blade. By then, the city’s sewage was being diverted along pipes offshore, and water quality inshore had substantially improved. Still, though, the shallow, rocky reefs remained empty of crayweed.
In 2011, a team of scientists at the Sydney Institute of Marine Science decided to test whether crayweed could grow again in the empty areas. They took mature adults from existing seaweed forests north and south of Sydney and transplanted them into the forty-mile gap, fixing them to bare rocks with plastic mesh and cable ties.l Six months later, some of the transplants had survived, and they were busy scattering the next generation of young sporelings across the seabed.
From that initial success, Operation Crayweed was born. Restoration efforts were scaled up, initially paid for by a crowdfunding campaign in December 2015 that prompted people to “plant an underwater tree for Christmas.” Support from members of the public was critical in kick-starting the project, paving the way for state investment. Operation Crayweed is also reaching beyond the science of reforestation and rolling out art installations and exhibitions along the coast to make new connections between local people and the lost forests. Schoolchildren dressed up as sea dragons and octopuses have been parading along the Sydney seafront, imagining what it’s like to be these animals living in the underwater forest that’s regrowing just offshore. Previously, many Sydneysiders didn’t realise the city’s water quality had greatly improved, and they had no idea crayweed forests used to grow on their doorstep. Now, at more than a dozen sites across the city, people can look out to sea at the marker buoys and know that’s where the forests are coming back, gradually filling in the gap in these easterly reaches of Australia’s Great Southern Reef.
In another part of this immense network of underwater forests, ancient human connections that have remained unbroken for millennia are now at risk of coming to an end. In lutruwita (Tasmania), the shark tooth–shaped island south of the Australian mainland, Aboriginal people traditionally hunt for food in the giant kelp forests of their sea country and use the kelp as an important material to make objects such as water-carrying containers. Aboriginal women visit kelp forests at low tide to collect seashells, including maireener, or rainbow kelp shells, which they rub with sand to reveal the shining mother-of-pearl underneath. These and other tiny shells are pierced, threaded into necklaces, and used as gifts and tokens of honour. Maireener shells are now much harder to find, and shell necklaces could become a lost art because lutruwita’s giant kelp forests are disappearing.
In recent years, propelled by climate change, the warm ocean current that flows polewards along the east coast of mainland Australia has been pushing farther south. This is the prime reason why the seas around lutruwita are heating four times faster than the global average, and why the lutruwita giant kelp forests are dying. There are bays where, just a few decades ago, fishermen cut channels through the giant kelp to get their boats in and out, and now there’s no kelp at all. Only 5 per cent of lutruwita’s giant kelp forests still stand, and that 5 per cent could hold the secret for the future of the forests.
People from the weetapoona Aboriginal Corporation have been collaborating with marine biologists from the University of Tasmania to trial a new form of restoration they hope will see the return of kelp to their sea country. They selected Trumpeter Bay, on the southeast coast of lutruwita, as a site where kelp have been outplanted in the hope they will kick-start the return of lost forests.
These outplantings originate in the surviving naturally occurring stands of kelp dotted around lutruwita. Cayne Layton and his team at the university visited some of the remaining patches of kelp forests and collected spore-producing fronds, leaving the intact adults behind. In the lab, the fronds released spores, which developed into microscopic kelp females and males, known as gametophytes, which look like tiny twigs. These form an important stage in kelp’s unusual, two-phase life cycle, a part that’s normally hidden from view. Minute females and males produce eggs and sperm, which fuse and grow into the large kelp that form the structure of a forest.
Conveniently, this miniature, gametophyte stage can be cooled and stored under red light, which arrests its development; and more gametophytes can easily be made by snapping the tiny twigs in two. It’s a practice perfected in Japan and Korea, where kelp is important food, much of it reared by the aquaculture industry. Cultures of kelp gametophytes have been kept alive in cool storage for decades.
In lutruwita, Layton and colleagues store their kelp gametophytes in a refrigerator the size of a hotel minibar. This is a compact, living repository, the kelp equivalent of a seed bank. It provides material for Layton’s studies in rearing lab-grown sporelings in aquarium tanks at different temperatures, to identify those that can naturally cope with heat. Some young kelp even grow well at seventy-four degrees Fahrenheit, way above temperatures the kelp parents would have experienced in lutruwita’s warming sea.
Layton’s team reared more of these super-kelp strains and transplanted them into the wild, including in Trumpeter Bay. As expected in the turbulent seas of lutruwita, not all the trial outplantings have taken hold. But enough are surviving to show the technique works. Crucially, some of the super-kelp have now reached maturity in the wild and are producing their own spores, like the crayweeds in Sydney. This is the main aim of the lutruwita initiative, to put enough kelp back in the ocean to kick-start the natural cycles, so that ultimately forests regenerate by themselves—and hopefully keep growing as the ocean continues to warm.
There is no silver bullet for creating future-proof, self-sustaining underwater forests or, for that matter, any other important green habitats in the ocean. In lutruwita and elsewhere, restorationists are busy testing out ways to replant and restore kelp forests, seagrass meadows, and mangrove forests. They’re showing that restoration is doable, but it’s complicated and nuanced. Each species and habitat in each region will likely need its own methods and solutions. And that’s going to require much more funding, in many more countries, to support the kinds of detailed research and scientific trials that are exploring what works best. So far, successes in restoring lost kelp forests have mostly been modest in size, but they are showing what’s possible. The obvious next big steps will be finding ways to effectively scale up, while avoiding the pitfalls that other restoration efforts have crashed into.
The future of kelp forests will depend on finding practical ways of keeping these ecosystems alive in the changing ocean, ideally without having to sell out to carbon markets. And perhaps more than anything, it will depend on weaving underwater forests more deeply into people’s lives and minds. The greater the number of people who know and care, the less likely it is that the ocean’s forests will be allowed to disappear.
a Brown seaweeds are included within the proposed kingdom Chromista, and they are a taxonomic class, Phaeophyceae, within which is the kelp order, Laminariales.
b I think it looks like the lollipop-shaped Truffula tree from Dr. Seuss’s book The Lorax.
c Red seaweeds, or rhodophytes, belong to a separate kingdom and are more closely related to land-based plants than kelp are.
d This is described as echinochromicity, after the echinochrome pigments found in sea urchins, which happen to have antiviral and antibacterial properties and have been investigated as potential therapeutic drugs against Covid-19.
e Sea urchins, starfish, sand dollars, brittle stars, feather stars, and sea cucumbers are all echinoderms, a phylum of animals named for their spiny skin (from the Greek word echino, meaning “spiny,” and the Latin word derm, meaning “skin”). Within the echinoderms, sea urchins belong to the echinoid class.
f Or starfish, as they are interchangeably called by people (like me) who aren’t too bothered by the ichthyological overtones.
g At the time of writing.
h I doubt it will ever be possible to rear such animals as great white sharks or blue whales in captivity, and I hope it never comes to that.
i The Sargasso Sea forest contains two (out of several hundred) Sargassum species, Sargassum natans and S. fluitans.
j Meaning “rocky-shore denudation” or “sea desertification.”
k Phyllospora comosa forms habitat that’s used by rock lobsters, known locally as crayfish, hence the common name crayweed.
l Restorationists are well aware that deliberately adding plastics to the ocean is not ideal, and they are seeking alternatives that will be robust enough to withstand the waves and strong currents.
Chapter 9
Future Reefs
Several things I remember vividly from my first visit to a coral reef. The water was a lot warmer than I expected—it was like jumping into a bathtub—and I could see much farther into the distance than I ever had before underwater. After two years diving in British seas, I knew what it felt like when my face got so cold I returned speechless from a dive, and that one can lose sight of a dive buddy from only an arm’s length away. Most of all, the first coral reef I saw was even more colourful than I imagined it possibly could be. There were fish in yellows, purples, and electric turquoise blues, and mauve corals and emerald sponges. All the colours were an obvious sign that I’d arrived in the tropics, a reality that I found exhilarating and terrifying all at once. I was fresh out of high school and slowly getting over a crippling home sickness I had not anticipated. Of course, a few days later, I wanted to stay forever, exploring the reefs, learning the names of everything that lived there, and doing my part, so I hoped, in helping to protect this extraordinary place from harm.
I was in Belize, on Turneffe Atoll, midway along the Mesoamerican Reef, which runs south from Cabo Catoche, Mexico, along more than five hundred miles of coastline, taking a sharp eastern turn to the Bay Islands of Honduras. The coral-reef complex there is the biggest in the world after Australia’s Great Barrier Reef. I had joined a team of divers tasked with mapping the underwater habitats and species of the atoll. Our daily routine was to head to the reef, morning and afternoon, and swim along straight lines, noting down in waterproof notebooks the life forms we encountered along the way. Four scuba divers would work together, each focusing on a particular component of the ecosystem. One diver catalogued the corals, noting down species and estimating what percentage of the reef was covered in live growth of corals—a key indicator of reef health. Another diver looked for invertebrates, all the crabs, shrimp, sea cucumbers, and sea urchins. The third diver was the fish spotter, my favourite underwater assignment. I might have seen more than five hundred species, and out of those I got to know well a hundred or so: hogfish and porkfish; blennies and ballyhoos; midnight, princess, and stoplight parrotfish; queen, grey, and French angelfish; golden, shy, and indigo hamlets; squirrelfish, trunkfish, soapfish, and jawfish.
The fourth diver in the group was responsible for navigating the rest of the team through the water and carrying a line to a floating buoy so the boat captain at the surface would know where we were. While I was doing that job, steering the rest of the team along their straight lines, I began to notice the reef around me was changing.
To navigate while diving, I used an underwater compass, setting a bearing and making sure to keep the needle in line as I swam along. A trick I soon learned was to find my bearing, fix my eyes on a large coral or sponge in the right heading, and swim towards that. A month or so into the expedition, I realised I was picking out and aiming at pale-coloured corals. They shone through the water and were the easiest to make out in the distance—but they hadn’t been there during our earlier dives. The underwater seascape was leaching colour and turning white.
Started to notice a lot of coral bleaching, especially the mountainous star.
That line from my dive logbook from October 4, 1995, referred to a species of Orbicella, a common Caribbean coral. By then I had seen many of these huge mounds, which from afar looked like olive-green blankets draped over boulders and up close were covered in small, raised bumps, some of them outlined in a neon-green ring. Those bumps were coral polyps, which lived together in the hundreds and thousands and built colonies up to ten feet across. An individual coral polyp with its soft tentacles extended looks like a little flower nestled in a stony cup, which the polyp secretes around itself from the mineral calcium carbonate. Orbicella and hundreds of other coral species are generally known as stony corals, or hard corals, because of these limestone skeletons, which feel sharp to the touch. Lodged inside living tissue of a coral polyp are millions of microscopic spheres of single-celled algae known as zooxanthellae.a These algae are photosynthetic, soaking up sunlight and providing food for the whole coral colony in exchange for a secluded place to live in the shallows with a good supply of sunshine. It’s a symbiosis that both corals and zooxanthellae benefit from, but the relationship can break down when conditions become stressful, such as when the sea around them heats up. The warmth shifts the algae into overdrive, and they photosynthesise much faster than normal and produce lots of damaging oxygen-free radicals. The polyps respond by ejecting the zooxanthellae from their bodies. Pigments in the zooxanthellae are what make corals colourful, and when they’re gone, all that’s left is a thin, transparent layer of coral tissue, which shows the bone-white limestone skeleton underneath. It looks like someone poured a bottle of toilet cleaner over the colony.
A scribbled note in my dive log from Belize mentions that recent warm, calm weather all over the Caribbean was causing outbreaks of coral bleaching. At the time, I knew about bleaching only in an abstract sense, and evidently, I had no idea what was really at stake. A puzzling remark in my logbook reads:
This is the movement of biodiversity as we watch—exciting but maybe something to worry about?
It was the first mass coral bleaching in Belize in living memory. My dive buddies and I were among the first to knowingly witness the colour of these reefs fading away. Temperatures in Belizean waters that summer were almost one degree Celsius warmer than at the same time the previous year. For weeks, the temperature stayed high enough to stress many different types of corals and trigger bleaching along hundreds of miles of reef. A similar scenario was playing out across the region. That year saw the first known cases of mass bleaching on reefs in Cuba and Honduras; and coral reefs turned white in the Cayman Islands, Jamaica, Dominican Republic, Puerto Rico, Curaçao, and Bonaire.
When corals bleach, they don’t necessarily die right away. Without their zooxanthellae, most corals struggle to get enough food, but if they can keep going long enough, their polyps will eventually absorb new algae from the seawater around them. Then the colonies regain their colour and carry on growing.
In Belize, the bleached corals began to show signs of the living tissue dying off. It could have been much worse, but in the nick of time, the atmospheric conditions shifted, and hurricanes stirred. I remember sitting on the beach at night, watching thunderstorms rage in the distance. And for a time, our base camp stayed on evacuation alert as several hurricanes passed through the region. I didn’t know it at the time, but that hurricane season cooled the sea enough to ease the coral bleaching. Within six months, many coral colonies in Belize had recovered.
But this was only the beginning of the troubles for Belizean corals. Three years later, in 1998, another mass bleaching struck, much worse than the first, when a massive ocean heatwave, associated with one of the most powerful El Niño events on record, swept around the planet. In 2005, the reefs of Belize bleached again.
Early in my studies of coral reefs, I was caught up in the same desires that I bet many other marine biologists have felt. I wanted to see reefs for myself and try to wrap my head around these staggeringly diverse ecosystems. Coral reefs grow in shallow, tropical waters around the world, in more than one hundred countries, with major clusters in the Caribbean Sea, on islands dotted through the Pacific Ocean, in the western Indian Ocean, in the Red Sea, and along the east and west coasts of Australia; the most biodiverse reefs are in the Philippines, Indonesia, Papua New Guinea, and the Solomon Islands, a region known as the Coral Triangle. Collectively, the world’s coral reefs cover less than 2 per cent of the ocean surface, an area roughly equal in size to Ecuador,b and yet they pack in one in every four known ocean species. Counting and cataloguing the number of species that exist in the ocean goes something like this: fish, octopus, shark, reef shark; sea cucumber, sea urchin, crab, reef crab; worm, worm, worm, reef worm.
A healthy coral reef flaunts its diversity and sheer abundance of life to anyone who sticks their head in the water and looks. Even more life is small and hidden away within the reef’s recesses, requiring more careful looking. Nature photographer David Liittschwager created an intimate view of reef life when he nestled a square metal frame, each side one foot long, onto a reef in Mo’orea in French Polynesia. He then catalogued and photographed every living organism visible to the naked eye that swam, crawled, or floated through that cubic foot of water during the course of a day. His crowded, composite image shows just how much life exists, even in one small space on a reef.
The unique biodiversity alone makes coral reefs supremely important parts of the living planet, and there are many other reasons they matter. In purely economic terms, coral reefs are a global asset estimated to generate close to $3 trillion each year in goods and services, roughly equal to the global commercial banking sector. Reefs support tourism outfits and attract visitors from all around the world who want to experience these dazzling ecosystems. The value of reefs lies in plenty besides tourism revenues. Coral reefs hug coastlines and guard them against storms and erosion; they form nurseries for fish and other animals that are caught in surrounding seas, and they create untold, deep cultural connections to the communities that have always lived alongside them. Reefs are central to the lives of coastal people across the tropics. Worldwide, more than one hundred million people live within an hour’s walk of a coral reef; close to a billion people live within sixty miles. Most of these people live in low-and middle-income countries, and the security of their food, livelihoods, and homes is directly underpinned by healthy reefs. These are the people whose lives are being transformed as the world’s reefs change.
