A Sea of Glass Page 12
When I talk about the Blaschka collection as reaching back through time, I mean back over the relatively small 160-year stretch encompassing industrialization, not back 360 million years to the Devonian era. Yet when we look at the glass feather star models, this is what we are seeing: a fossil in glass that dominated the planet millions of years ago. Back then, Devonian-age stalked crinoids called sea lilies stretched to over 100 feet long and carpeted the ocean floor. While I wouldn’t find feather stars that big today, they are no less spectacular in their contemporary form. To easily find living representatives of feather stars, we have come to the Coral Triangle, the center of echinoderm biodiversity.
Once we have set our survey lines by laying a thirty-foot measuring tape across the reef, we begin to identify and count corals. These corals, at such a high-current site, look terrific, with bright colors and no encroaching algae or microbial diseases. Under normal conditions, we would have floated above the reef, filling our slates with species lists and health checks, being careful not to touch anything on the bottom. But here we can hardly hold onto nearby rocks to avoid getting pulled away by the current, let alone write on our slates. We persevere until it’s time to reel in our survey lines and drift back with the current. Adah’s hijab billows behind her like a cape. I am relieved that she managed her extra layers so effortlessly along with intensive fish surveys in high currents.
As we float with the growing current and fading light, the reef edge spreads before us like an underwater tapestry of reds, blues, oranges, yellows, and greens. I am struck, as always, by the magic that is the biology of the coral reef ecosystem. When healthy, reef ecosystems are a brilliant spectacle of life, fueled by the coral’s solar-powered cells. Clown fish dart between anemone tentacles, a mantis shrimp peers from its burrow, bright orange and blue hydrocorals grow, and a barracuda prowls for less cautious reef fish. We move on, zillions of tiny red and yellow fish darting into the branching coral for cover as we pass.
Then I glimpse what I hoped most to see: the feather stars as they come out to feed. During much of the day, they hide in the reef or in branches of corals, their long spindly arms curled into a tight ball. As the sunlight fades, they rise up from hiding and make their way to the highest points of the reef, surprisingly mobile for something that looks so rooted and stiff. They unfurl their long, colorful spiked arms the same way a fiddlehead fern unfurls in the spring, except in minutes instead of weeks. Once unfurled, they spread their eight-inch-long arms wide in the current to capture microplankton, creating a multicolored spectacle, each crowding against the other for the highest spot near the greatest current (page 140).
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Collectively, echinoderms are the most iconic and ecologically important of all the marine invertebrates, and the Blaschkas spared no talent in depicting the varied symmetry of this group in watercolor and glass, portraying sea stars, ancient feather stars, brittle stars, and the unassuming sea cucumber, which, though tube shaped, is no less a star. Despite the range in their appearance, these are all echinoderms, a name that means “spiny skin.” Most have fivefold symmetry, whether it is expressed as arms in multiples of five or, in the case of the sea cucumbers, five rows of tube feet running along the wormish body. Echinoderms seem alien when you consider the improbability of how they actually function. Anyone who has ever watched a sea star walk, for instance, will know what I mean. While most sea stars have five arms, some, like the sunflower star in the Pacific Northwest, can have from sixteen to twenty-four arms, and each of these arms might have a hundred tiny suckered tube feet underneath, each a quarter of an inch long. A sunflower star is nothing short of spectacular, a lion of the underwater, three or even four feet across and capable of chasing down prey, like scallops, by actually running along the sea floor at a rate of three feet per ten seconds. Before the huge sea star mass mortality in 2013–14, they were as abundant as dandelions in the Washington subtidal. The ones we grow in our tanks at Friday Harbor Labs can even snatch a falling clam in midwater, like my dog catches a ball. To run across the bottom like they do, all 500 to 1,000 tube feet need to grab and release their hold on the sea floor in a perfectly coordinated way. This far exceeds the complexity of how a millipede walks. Each tube foot relies on a hydrostatic skeleton, which is a muscular, fluid-filled cavity, and the creation of suction on the bottom of the tiny foot, which is just wider than a cat’s claw. The grabbing and releasing is somehow orchestrated through a complicated water vascular system with valves and check points, activated by a fairly simple nervous system.
Feather stars in Indonesia: a crinoid feeding on a reef in Bali (top) and Drew watching a crinoid on a high current wall near Kapota Island. Photos by Drew Harvell (top) and David O. Brown.
If understanding how a sea star walks is complex, consider how some feed. Carnivorous sea stars such as the ochre or sunflower stars evert their entire stomachs onto or into a prey item, such as a clam, use digestive enzymes to turn the body of the animal into a slurry, and then absorb it. But first they have to use their tube feet to open the clam by brute force so they can insert their stomach. While the best-known sea stars are indeed predators, feeding on bivalves, barnacles, worms, snails, and even other stars, their close relatives, the sea urchins, are almost exclusively herbivores, eating algae. Some, however, are equal-opportunity omnivores that will happily munch on small crustaceans or sponges that come with the algae. Brittle stars and feather stars are completely different and feed on very small things, using feathery arms to filter plankton from the surrounding water, or hoovering up sand grains coated with organic matter. Sea cucumbers, unlike many of the sea star species, are exclusively nonpredatory and feed either by filtering plankton or by consuming detritus from the mud. However, lurking within even this simple feeding mode are new discoveries, such as the recent one that some sea cucumbers can multitask and feed with both their mouth tentacles and their “respiratory trees,” which are tucked inside their anus (Jaeckle and Strathmann 2013). It’s handy to have a backup for feeding, because when attacked by predators, sea cucumbers eviscerate their entire digestive system as a defense.
Ecologically, many cucumber species are ecosystem engineers, as are worms. We see them commonly in both temperate and tropical oceans, deposit-feeding and bioturbating soft sediment communities, which helps oxygenate deeper sediments. Although some sea cucumbers are drab and wormlike, those crafted by the Blaschkas have striking colors and patterns. The Blaschkas depicted a shimmering diversity of both temperate and tropical sea cucumbers in glass. Their Trachythyone is a sparkling wonder of iridescent purple tubercles set in a body of mottled blue (page 143). Contrast this with the smooth brown body and flat feeding tentacles of Synapta fasciata.
The length and coils of the sinuous, ciliated arms of the Blaschka brittle stars, in both watercolor and glass, are truly epic. Those glass arms are also very fragile, as evidenced by the pile of brittle star arms belonging to Ophiothrix serrata that we found in one of our dusty boxes at the Corning Museum of Glass’s offsite storage facilities (page 145). A century of being shuffled around had left the needle-thin arms in a clutter of broken sections. This piece has now been restored in preparation for a large 2016 exhibition at the Corning Museum. Brittle stars like Ophiothrix serrata feed by deploying these eight-inch-long ciliated arms high into a fast current and catching microscopic phytoplankton on their tiny tube feet. I have seen them on day dives in the Caribbean, tightly wrapped into the reef or entwined in a mesh of sea fans. At night, they perch as high as they can get on the tops of soft coral colonies, or even seagrass blades, to snag passing food.
Echinoderm diversity in glass (clockwise from top left): Mediterranean crinoid Antedon mediterranea; photo courtesy of the Corning Museum of Glass. Brittle star Ophiothrix serrata; photo by Guido Motofico, courtesy of the Natural History Museum of Ireland. Sea cucumber Synapta fasciata, with smooth body and no tube feet; photo by Kent Loeffler. Sea cucumber Trachythyone peruana; photo by Kent Loeffler.
Every
brittle star is a gem of long, winding arms and often brilliant, colorful patterning on the central disk. Ecologically, they can be abundant enough to be important as a food source for hungry predators, and we have a high diversity of them in the Pacific Northwest, including the Blaschka match Ophiopholis aculeata (page 145). They are a small but important component of our oceanic biodiversity that is not present on conservation checklists and could slip silently away without being noticed. This is the opposite of the case of their close cousins, the sea stars.
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Of all the echinoderms the Blaschkas shaped into glass, the sea stars are among the most important ecologically. The five-armed sea star, a so-called keystone predator, reigns supreme in tropical and especially temperate marine ecosystems. A keystone species is one that exerts a disproportionate impact on the shape of its community, whether it’s a beaver damming rivers and creating a wetland or a sea star trimming back common mussels to make room for rare species. The term “keystone” was coined back in 1969 by my former postdoctoral adviser Bob Paine, from the University of Washington, in describing the transformative effect of removing ochre stars from shores in the Pacific Northwest. Bob, a distinguished marine ecologist, popularized the use of experiments in piecing together the linkages in natural marine ecosystems. In the 1960s, he hypothesized that the ochre star was master in determining which other animals could live in the intertidal region. In a foreshadowing of what nature is doing on those same shores today, he took all the stars off sections of the rugged rocks of Tatoosh Island on the outer Washington coast. The response was a change in the entire appearance of the intertidal. In the absence of their keystone predator, squirrel-sized mussels outcompeted all other animals and plants and took over space on the rock. A multicolored seascape of diverse sea anemones and sponges and sea squirts was replaced by what looked like a huge glacier of dark mussels spreading upward from the deep. As a graduate student, I was inspired to visit Tatoosh Island with Bob and listen to him brag about his “mussel glacier” and see the shocking difference in the intertidal sites where he had removed the ochre star. What would it look like if most of these keystone star species were removed from our waters? I can tell you firsthand.
Ophiothrix serrata brittle star before (left) and after restoration. Photos by Elizabeth R. Brill (left) and the Corning Museum of Glass.
Daisy brittle star (Ophiopholis aculeata) in glass (left) and alive. This is one of the most common brittle stars and is distributed worldwide. We saw this one in Friday Harbor, Washington. Photos by Elizabeth R. Brill (left) and Drew Harvell.
In the winter of 2013, dead and dying sea stars littered the beaches and tide pools of the Washington coast. I stood on the rocky beach, the glittering lights of the familiar Seattle skyline across Elliott Bay, and took in the carnage that lay before me. The beach, from water’s edge to high up in the rocks, was littered with the arms and twisted bodies of three species of sick stars, including ochre stars. Laura James, Chuck Greene, and I counted over 150 stars on the beach that night, and over half of them were falling off their rocks, losing arms, or had gaping lesions. I had been called to sample the dead stars on this beach by Laura James, an intrepid Seattle diver. She had earlier commented that she was witnessing “the change of her lifetime” as nineteen species of the very rich sea star diversity surrounding Seattle were dying at all her best dive sites. I’d been following the spread of this epidemic since August, but it hadn’t affected the San Juan Islands yet, and it was ominous to see our three dominant species of star melting away within sight of Seattle’s lights. Part of the dread was that the syndrome, known as “sea star wasting,” had been thought to affect only a single species and only during the warm months. Now we were seeing it in colder winter waters. This was a new and unsettling development, and we had no idea what was killing the sea stars; it was either a new, undescribed infection, a further decline in the ocean’s pH, or even something else.
Healthy populations of the keystone star Pisaster ochraceus eating back the mussel bed in Bamfield, British Columbia. Photo by Drew Harvell.
At the time of this writing in 2015, at least twenty species of sea stars from Alaska to Mexico are still experiencing mortality, disappearing in piles of spicules and detached arms. It begins with the star looking a bit flattened and deflated, then lesions appear on their arms, and then suddenly an arm walks away and organs spill out. By 2014, sea stars had become rare in places they were once abundant and iconic, from California all the way up to Washington State. Our Alki Beach observation in December 2013 was important because it occurred in cold water, and stars on other cold beaches stayed healthy. Many other star populations in Washington and Oregon did not decline until the summer warming hit, fully six months later. The epidemic had actually started a year earlier on the East Coast, where it devastated populations of the Blaschka match common sea star, Asterias rubens (page 136).
Laura was surprised to see over a hundred stars still alive on that beach, since on dives to the subtidal waters below, she had recorded thousands dying. She showed us video footage of them falling off the pilings into huge piles of spicules. This same footage, coupled with environmental reporter Katie Campbell’s compelling story for CNN, would in 2015 win them a shared Emmy Award for environmental reporting. That night at Alki Beach, half the ochre and mottled stars fell apart, leaving the beach littered with still-moving arms. The other half died in the following two weeks, leaving a body count of over two thousand dead stars at the one site. This mass mortality continued into January at certain sites around Puget Sound, including Alki Beach, Tacoma beaches, and Mukilteo. Adding to the mystery, stars in the nearby San Juan Islands remained healthy through March (Eisenlord et al., in review).
However, by the end of summer 2014, our stars in the San Juans had also suffered a massive hit, and we had solved one big mystery—the cause of the epidemic. It turned out to be a killer virus. After three months of detailed molecular work sifting through thousands of bacterial and viral genetic sequences, Ian Hewson from Cornell identified a candidate virus. Further experimentation by Colleen Burge and Morgan Eisenlord, also working in my lab at Cornell, confirmed it. They injected fifteen healthy sunflower sea stars with a slurry of virus-sized particles from sick ones. All became sick and died, while the controls remained healthy (Hewson et al. 2014). Here was the sad evidence that one of our most important ecological keystone species was taken down by the smallest of infectious agents, a virus. It also represented a new and foreboding discovery about the triggers of ecosystem collapse.
This is the largest disease epidemic of unfarmed species ever seen in the oceans, and it has, for now, robbed our shores of once bright sea star biodiversity. The populations of over twenty species have been decimated, including those of the iconic purple, orange, and pink gem-like ochre stars that grace half the T-shirts sold in the San Juan Islands and that are beloved of every child who plays on those beaches. As of 2015, ochre stars are completely gone from many California shores and are rare on Washington shores. The giant sunflower star (Pycnopodia helianthoides), once as common underwater as starlings are in the air, is completely missing from our deeper subtidal waters. Disease, under the ocean as well as on land, is one of the silent thieves of biodiversity. This epidemic was well studied because it spilled into the intertidal and was seen by many people.
Will the ochre star and the other nineteen species affected recover? It depends on whether the new baby stars recruited to our shores in the fall survive the next season. It depends on whether stars evolve resistance to this new killing virus. It depends on whether the levels of ocean acidification increase and interfere with the successful free-spawning of the few surviving stars. Sea stars are in the group that has been identified as vulnerable to increasing levels of acidification, both because they free-spawn in the ocean, exposing the critical fertilization process to pH stress, and also because the developing larvae have fragile skeletons dissolved by corrosive waters. The eventual recovery of the sea stars also
depends on how far north the killing epidemic spreads, since Alaska is the last refuge for these endemic stars. All we can do now is wait for the answers in the next warm season.
Infectious diseases are silent killers that stalk our oceans unseen. As with human diseases, the probability of a wildlife outbreak depends on the relationships among the pathogenic microorganism, the host, and the environment. A change in any one of the three can trigger an outbreak. We are still trying to understand the role of changes in the environment, like warming oceans and coastal pollution, for the sea star epidemic. We do know of other cases where underwater biodiversity has taken a big hit from disease that was aided by warming waters. Two species of Caribbean coral and two species of California abalone have been driven onto the endangered species list by disease (Burge et al. 2014), coupled with warming waters. In 2014 alone, twenty species of coral were added to the endangered species list (Keller 2014), nudged to endangerment by losses from disease. Large mammals such as dolphins, seals, and sea lions have suffered catastrophic losses in multiple large epidemics as well (Burge et al. 2014). It’s also worth remembering that on land, the chytrid fungus of frogs and salamanders has already driven perhaps a hundred species to extinction (Crawford et al. 2010). Infectious diseases have the same potential to drive species to extinction in the oceans; it’s just vastly harder to detect these events. The unusual susceptibility of some echinoderm and coral groups to disease is a sentinel, like the canary in the coal mine, warning us to take heed of looming danger. How many other, less iconic or less visible underwater species have already been silently stolen by disease? Certainly, no one is watching the health of feather stars or brittle stars in the high-current waters of Bali.