Autumn arrived on a night wind along the Strait of Georgia, the Pacific Ocean waters between Vancouver Island and the mainland of British Columbia. The next day, a cold snap whipped waves into whitecaps as a research vessel maneuvered into position in a fjord known as Howe Sound. On deck, a crewmember closed the vaultlike hatch of the Aquarius, a fourteen-foot-long submersible.
Swaying like a Ferris-wheel chair, Aquarius was lowered to the ocean surface on a cable above the ship’s stern. Waves splashed against the bubble, and the craft gently sloshed back and forth. From inside, the view changed to the light blue-green of the sea.
The natural light faded as Aquarius slowly descended to the seafloor. Illuminated by the sub’s light beams, creatures as bizarre as those in the works of Jules Verne came in sight. They loomed through the sub’s lens like forests of white, yellow, and orange bushes: glass sponges, organisms with surprisingly successful adaptations to the deep’s harsh conditions. Some had gaping openings known as oscula, while others beckoned with undulating fingers. Still others were masses of snow-white frills.
“At one time, however, we didn’t think we’d spot something long believed extinct: glass sponge reefs,” says Sally P. Leys, a marine ecologist at the University of Alberta, Canada. “We now know that these fragile reefs-of-glass thrive in the depths off the Pacific Northwest.”
Indeed, not long before the Howe Sound dive, researchers had discovered glass sponge reefs in Portland Canal, an arm of Portland Inlet, part of the border between southeastern Alaska and British Columbia. Despite its name, the “canal” is a fjord. It extends seventy-one miles northward from Pearse Island, British Columbia, to Hyder, Alaska. Glass sponge reefs have now been documented along the Pacific Coast from the southernmost major fjord, Howe Sound, to the northernmost Alaskan fjord at Lynn Canal, a distance of 800 miles.
“Journey to the Sea of Glass” was the first submersible expedition to the bottom of Howe Sound. Leys found her quarry everywhere she looked.
“The deep was alive,” she says, “with glass sponges.”
In the far distance, their long-dead relatives looked on. “Mummies,” they’re called, these strange shapes that form one of the largest structures ever to exist on Earth.
Stretching overland some 1,800 miles from Spain to Romania is a fossil reef, a sinuous curve of millions of mummies that were once living, vase-shaped animals. In its heyday during the Jurassic Period, from 200 million to 145 million years ago, the reef was larger than today’s Great Barrier Reef off Australia’s northeast coast. Now it’s visible only in outcrops dotted across southern and central Spain, southeastern France, Switzerland, southwest Germany, central Poland, and eastern Romania near the Black Sea.
The ancient reef was made up not of corals, but of deep-sea sponges called hexactinellids. Unlike corals, which build a skeletal structure of calcium carbonate, glass sponges use silica dissolved in seawater to manufacture a skeleton of spicules—tiny four- or six-pointed siliceous “stars.”
Individual glass sponges, such as the beautiful Venus’ flower basket sponge (Euplectella aspergillum), are still found in the deep sea, but those species belong to a different order from the Jurassic reef builders. The reef-building glass sponges, scientists reasoned, went extinct 100 million years ago, driven out by competition from newly arrived diatoms, single-celled algae that use the silica in seawater to build cell walls.
Or did they?
For millennia, the darkness beneath the waters northwest of Vancouver Island—Queen Charlotte Sound and Hecate Strait— concealed the next chapter in an eons-old tale.
The first hint that something odd might be at the bottom of Hecate Strait came during a 1984 seafloor mapping expedition. Using sonar imaging, scientists from the Geological Survey of Canada saw mounds over huge areas of the seafloor—places that should have been completely flat. Similar acoustic anomalies, as geological survey scientists Kim W. Conway and J. Vaughn Barrie referred to them, were observed again in 1986 during a survey of Queen Charlotte Sound.
Reef-building glass sponges gave up their secret to Conway and Vaughn in 1987: underwater photography in Hecate Strait captured the sponges on film. Far from extinct, the sponge reefs were thriving in the depths off British Columbia. Diatoms need the sunlight of the sea’s euphotic zone and so don’t live in the deepest parts of the ocean. The depths had remained an open niche for reef-building glass sponges.
Until the discovery, knowledge of glass sponge reefs was limited to the fossilized reefs of Europe, studied by paleontologists such as Manfred Krautter of the University of Stuttgart in Germany.
“When I first heard about the sponge reefs, I was electrified,” says Krautter. “It was like finding a living dinosaur walking around.”
In 1999, Canadian and German scientists, including Conway and Krautter, descended to the depths of Hecate Strait in a submersible for a firsthand look. Glass sponges, they found, not only were alive but had formed reefs that extended as far as a submersible porthole view could see.
The sponge reefs—some of which are 9,000 years old, 60 feet high, and 270 square miles in area—are all at or below 500- to 650-foot water depths. “That’s why we didn’t find them for so long,” says biological oceanographer Verena Tunnicliffe of the University of Victoria.
The reefs occur as bioherms, or mounds, and as biostromes, or sheets. The sponge bioherms off British Columbia are steep-sided, six-story glass castles. The biostromes extend over distances many times the length of the island of Manhattan.
Individual glass sponges, whether freestanding or on a reef, grow from three-quarters of an inch to two and three-quarters inches per year. In some animals the rate is faster than in others, perhaps because they’re located in better feeding areas. Most grow more rapidly when they’re young, and, like us, slow down as they age. The largest known sponges are thought to be 450 years old.
Glass sponges were first sampled in the late nineteenth century during the Challenger Expedition, a pioneering four-year ocean research voyage. Since then, modern instruments such as scuba, submersibles, and remotely operated vehicles (ROVs) have vastly expanded our understanding of glass sponges and their environment. With an ROV like Canada’s ROPOS (Remotely Operated Platform for Ocean Sciences), it’s now possible to study the ecology and physiology of the sponges in situ.
Scientists have learned, for example, that glass sponges fall into two main categories, based on the type of skeleton the animals produce: those with a loose spicule skeleton, called lyssacine sponges, and those with a fused spicule skeleton that forms a rigid exterior, called dictyonine sponges. Glass sponge reefs are formed by the dictyonine type.
Non-reef-forming glass sponges are found in the depths of the Caribbean, the Indo-Pacific, and the North and South Atlantic. They’re also found in four places where the waters are shallow, but deep-sea-cold: Antarctica, the fjords of New Zealand, scattered caves in the Mediterranean, and the coastal waters of western Canada. To date the only known living glass sponge reefs are off the Pacific Northwest, including along the seafloor thirty miles west of Grays Harbor, Washington. Other glass sponge reefs may exist where there are favorable conditions, such as in the Bering Strait.
Three main species form living glass sponge reefs: Chonelasma calyx, the goblet sponge; Aphrocallistes vastus, the cloud sponge; and Farrea occa, which has no common name. The ocean environment off the Pacific Northwest offers an enticing locale for these reef builders. More than 13,000 years ago, glaciers covered much of Hecate Strait and Queen Charlotte Sound. Icebergs scoured their way along the continental shelf, leaving behind berms of coarse gravel. It was on these berms that the sponges likely began their construction.
The sponges turn silica from ocean water into long, sharp shards, which they mount together like sets of tent poles. The skeleton is formed as these small pieces, called spicules, are welded into a three-dimensional structure. As the sponges grow, the scaffold enlarges. Some 80 percent of a glass sponge is skeleton, “a delicate construction of glass that’s covered by a thin veneer of soft tissues,” says Leys. Young sponges attach to adults, building the glass palaces ever upward.
“The result is a solid structure of silica,” says Leys, “locked into a reef.” Like coral reefs, glass sponge reefs form with new generations growing atop the remains of previous ones.
The first three are found throughout the coastal waters of the Pacific Northwest. Water temperatures at depths where reef-building glass sponges live are between about 45 and 55 degrees Fahrenheit. Little light reaches the sponge reefs; all are in very deep waters. And levels of dissolved silica—low in both the Atlantic Ocean and the tropical Pacific—are high in the coastal waters off British Columbia.
The role of sediment in the lives of glass sponges is more uncertain. While some sediment is needed to cement the skeletons into a reef matrix, reef-forming glass sponges, which subsist on bacteria, don’t survive where particulates in the water are high.
Most animals that sluice water to feed—such as glass sponges—have ways of foiling sediment clogs before they happen, however. When sediment increases, an “off ” signal reaches all parts of the sponge and causes it to stop filtering. After a few minutes the sponge starts again, but if the irritation is still present it stops, “testing the waters” until they’re clear. “
Glass sponges are unusual animals because the majority of their tissue is one giant multinucleated cell called a syncytium,” says Leys. A reef-building glass sponge sends electrical signals through its entire body, in much the same way signals travel through nerves, but without the need for separate conductive structures. The signals can only propagate in cold water, because they use an exchange of calcium and potassium ions that requires low temperatures.
Glass sponge reefs’ invisible filtering is beneficial to every species in the ocean, says Leys. She and colleagues calculated that a reef one and a quarter miles long can process 21,000 gallons of water each second, “a breathtaking amount,” Leys says. “To get enough bacteria, their main food source, the sponges need to filter a lot of water. Glass sponges process many times their body
volumes of water each day.”
The reefs form one of the densest communities of deepwater suspension feeders, with up to forty oscula in one square yard of reef. That square yard clears bacteria from as much as 1,000 feet of water above it every day. Since the reefs are 500 to 650 feet down, “the sponges would easily deplete their food source if new bacteria didn’t arrive with currents flowing by,” Leys says.
The water the sponges “clean” of bacteria is recycled and—laden with carbon dioxide and ammonia—returned to the surface. High nutrients in waste products from the sponges promote bacterial growth at the sea’s surface.
Leys recently developed new instruments for measuring water and oxygen flow into and out of glass sponges. “So far, the records are superb,” she says, “showing a perfect drawdown by a sponge of all the water it filtered. Once we analyze the data, we will know whether glass sponges use more oxygen during periods of increased tidal flow.”
Ultimately, there’s “no free lunch” for glass sponges. Every bit of water they obtain costs them energy.
Adding another twist to the tale are the reef-building glass sponges that live in the open ocean west of Grays Harbor, Washington. Discovered in 2007 by marine geologist Paul Johnson of the University of Washington, they appear to be thriving on specialized bacteria that consume methane gas. The gas, a simple carbon hydrogen compound derived from organic matter in ancient sediments, flows out of the seafloor in copious amounts.
“While undersea methane seeps aren’t unusual,” says Johnson, “these sponges are sitting right on top of one—remarkable indeed.”
At other cold seeps, and at scalding-hot deep-sea hydrothermal vents, a cocktail of chemicals provides nutrients for bacteria that support entire animal communities. The methane gas beneath the Washington glass sponge reefs also could be fueling a food web.
“I’ve spent a lot of time looking at the exotic animals around hydrothermal vents,” says Johnson, “but glass sponge reefs and the ecosystem they support are even more incredible.”
Whether sustained by methane from beneath or by particles from above, glass sponge reefs provide habitat for an amazing variety of organisms, echoes Tunnicliffe. “They form the base of an ecosystem that extends well beyond the reef area.”
It extends to adjacent nonreef areas and to the dead reef skeleton framework, which, for some marine species, is more enticing than the sponge reefs themselves.
Wherever the seafloor is covered with sponge skeletons, openings of different sizes and shapes attract new tenants, including several that are commercially important. Juvenile and pregnant rockfish, for example, are abundant in both the living and dead sections of the reefs, indicating that all parts of a reef have a “nursery function.”
Nearby, octopuses are often arm-to-arm. Crabs are common, as are other crustaceans—shrimp, prawns, and lobsters.
“If you look at the reef and surrounding areas as one entity,” says Johnson, “it’s like an overcrowded aquarium in an expensive Japanese restaurant.”
All is not well in these deep-sea palaces of glass, however. Many have been severely damaged by fishing practices.
“The reefs off Washington seem to be completely trawled,” Leys says. “We might have discovered these glass sponges 100 years too late.”
In one reef off British Columbia Conway surveyed, living but broken sponges and dead sponge debris were common. The near-absence of rockfish at these damaged sites, compared with undisturbed reefs, where rockfish were abundant, indicated reefs that had been trawled.
“A startling summary of observations from the British Columbia groundfish bottom trawl fishery shows that between 1996 and 2002 about 253 tons of corals and sponges were harvested as bycatch,” states Leys in a 2007 paper, “The Biology of Glass Sponges.” Because they are noncommercial species, it’s thought that additional observations went unreported.
An analysis of the regions where the most bycatch happened showed twelve locations where 97 percent of all coral and sponge by-catch occurred. Many were next to or directly on glass sponge reefs. The effects were reduced after trawl fishers agreed in 1999 on a voluntary avoidance of the reefs. But landings continued in areas near glass sponge reefs.
In 2002, the Canadian government stepped in and mandated trawl fishery closures directly over the reefs. Despite these closures, however, new damage to previously unaffected reefs has been found. Researchers in submersibles have observed glass sponge reefs in Hecate Strait with broken skeletons, the remains piled in mounds on the seafloor.
“It was a shock to find that the northernmost reef in Hecate Strait has been damaged,” says Krautter. “What was once the most pristine part of these reefs will take thousands of years to recover—if it ever does.”
Brighter days may be ahead for glass sponges. In June 2010, Canada declared the reefs in Hecate Strait an “Area of Interest” for a Marine Protected Area, the last stage before their conservation can be legally established. CPAWS is working to secure fishing closures and protection for the Strait of Georgia glass sponge reefs, and to obtain international recognition for the Hecate Strait reefs. The latter would become a UNESCO World Heritage Site.
Otherwise, the glass sponge reefs of the Pacific Northwest may join their European counterparts in history. In death, their lovely silica glass bodies hollowed out and fossilized, they, too, will have become mummies.
To watch the video of Glass Sponge Reefs click here
To watch the video of Animals of the Reefs click here.