A Sea of Glass Read online

  A lot has changed in the 150 years since the Blaschkas spun their crystal creatures into being, including not only their conservation status and range in today’s marine environments, but also large upheavals in taxonomy. Bonellia viridis, our green spoon worm, is an example of the latter. In the Blaschkas’ day, it had its very own phylum, the Echiurida. The advent of modern molecular biology, however, downgrades the importance of its exceptional morphology and shows us that it is, instead, part of the fantastic variation within the vast phylum of annelid worms. On the upside, it may have lost its own phylum, but it hasn’t lost detectable ground in its distribution and abundance. The glass example we have in the Cornell collection is a female; the male is tiny, as small as a rice grain, and rare. He lives on or even inside the body of our larger girl. She lives in burrows in the sand and eats small animals or detritus. Her biggest feat is the production of an extremely toxic green pigment, bonnelin, which is capable of paralyzing small invertebrates and killing bacteria. It is so potent at killing bacteria that it is being researched as an antibiotic with applications for human health. What the Blaschkas could not have known is that both the nature of that chemical as well as sex is determined by the environment in which a baby worm finds itself. If it hits an abandoned patch of bottom, it turns into a female. If it lands near an existing female, the poisonous green pigment in her skin induces it to become a male (Jaccarini et al. 1983). This kind of sex-differentiating mechanism is thought by scientists to regulate population size. Considering what we have to learn from this diminutive but complex animal, it’s refreshing to know that it’s still common in our seas and widely distributed from the Mediterranean to the Atlantic and Pacific Oceans. My students, too, are heartened to know that the Age of Discovery is not over when it comes to searching out worms in their native habitats.

  Worms in glass (clockwise from left): Pherusa plumosa, Nereiphylla paretti, and Pista cristata alongside the sand grain tube it constructed. Photos by David O. Brown (Pherusa plumosa) and Gary Hodges.

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  As the Kingsbury inches us to the Creek Farm dock on the mainland, we are all anxious to get to square one for our worm hunt: an expanse of mud the size of two football fields. We’ve had to wait for a decent low tide, and it’s the first time off our very small island in two weeks. My student Reyn, always the organized one, remembers to grab the buckets and shovels as we step off the boat and head ashore. The tide flat, a vast expanse of brown mud, stretches before us, down to the glass water’s edge, with its usual muddish ocean smell, like a warm pond.

  Although the ground looks solid, I know differently. About halfway across, we hit the sucking mud and down goes the first student, tripped by a footfall that didn’t come loose. Although falling in the stinking mud could be viewed as bad, it comes with the territory for this group and only adds to the quest. Brad stands by to help Phoebe up and I watch nervously, hoping he won’t push her back in and start a mass mud fight this early in the trip. We slog through sucking mud to the water’s edge, eager to get as low on the tide as possible and start the dig.

  When you slow down to look, the mudflat is peppered with holes, burrows, and casts of all shapes and sizes. Casts are rather artful loops and even small volcanoes of coiled sand deposited by the worms after they have removed every bit of food value. We have a few tricks at our disposal to search out these unseen critters. First, it’s important to know what burrow or cast each species makes, and second, to dig fast to catch what lurks beneath. The third trick is to not sever your worm with the tip of the shovel or by pulling it too fast from the mud; worms have small, sturdy hooks for holding tight to the sides of their burrows. By the third hole, we are tired of finding just clams at the bottom. The point of this biodiversity class is to teach the lore of the mud, to recognize who makes the different-shaped and -sized worm and clam holes. We have three big goals on this dig, and they all involve worms. We need to find large clam worms, large burrowing lugworms, and something a little rarer, the parchment tubeworm, Chaetopterus variopedatus. David Brown calls our glass lookalike, Phyllochaetopterus major, a dragon (above). Its shimmering purple and gold likeness is indeed dragon-like. We won’t find the exact match, since P. major is a Mediterranean endemic, but Chaetopteris variopedatus is a close equivalent.

  The parchment tubeworm (Phyllochaetopterus major) in glass. We found a similar chaetopterid in False Bay, San Juan Island, and on mudflats in Portsmouth, New Hampshire. Photo by Gary Hodges.

  We are finding a lot of clam worms and they are really beautiful specimens—the archetypal worm, with a long greenish body that’s studded in every segment with paired appendages called parapodia, each ornamented with stiff, bristly hairs. This is as good as it gets for a worm—highly muscular and with versatile parapodia for burrowing, crawling, and paddling through the water. These mighty mobile worms, which can reach up to a foot long, are made for hunting smaller worms. They have highly developed sensory organs on their heads—tentacles loaded with chemo- and mechanosensory organs, eyespots, and grasping jaws. Suddenly, Phoebe yells, thrusts her hand into a hole, and slowly pulls out an impressive clam worm: eight inches of writhing Alitta succinea, bristling parapodia flashing in her hand. What Phoebe hadn’t realized is that these worms have really big jaws, and the clustered students scream as the black jaws pop out on the end of a sizeable proboscis, and Phoebe drops the worm. So it goes as the sun and steam rise over the mudflat: dig, yell, scream as each new worm surfaces.

  The really fun thing about a worm dig is the diversity we find; along with the clam worms, we also collect five different species from three different phyla: ribbon worms, flat worms, shimmy worms, acorn worms, and bloodworms. But our three other prizes—the parchment tubeworm, the calcareous tubeworm, and the lugworm—have so far eluded us, so we move on and try a different type of hole, one with a mud casting at its entrance. Soon enough, a bigger yell goes up, and Brad pulls the giant of all lugworms out of its deep burrow. This master burrower is eight inches long and designed like no other worm for the job of burrowing: a powerful ram-jet proboscis and a smooth body mostly lacking parapodia, except for rows of hooks on fleshy ridges, designed to grip the edges of the burrow (page 78).

  At first glance, it looks like a very plain brown worm, but on closer inspection, it’s actually iridescent green with a pair of bright red gills on its front segments. It looks much like Leopold Blaschka’s watercolor version. This is not a carnivore; it has none of the monstrous jaws found on species like the clam worms. Instead it has a powerful proboscis that excavates u-shaped burrows by first ramming the sand like a pile driver powered by strong muscular contractions, and then irrigating with a water current. It feeds like your basic earthworm, by ingesting and processing mountains of sediment and sucking organic matter off each tiny sand grain. Unlike the inside of our jellyfish, which has only two tissue layers and no real organs, these worms are packed with every organ an animal could want—high-pressure circulatory system, several pumping hearts, pharynx, gizzard, stomach, intestine, excretory system, reproductive system, and bright red gills that act like lungs.

  Burrowing lugworms in the family Arenicolidae: Blaschka watercolor (left) and live (Abarenicola pacifica). Abarenicola pacifica is common on a mudflat near my house on San Juan Island. Watercolor courtesy of the Rakow Research Library, Corning Museum of Glass, BIB ID: 121483; photo by Drew Harvell.

  My students are insatiable diggers, inspired by our high discovery rate, but we still don’t have a parchment tubeworm. To find them, we look for half-inch-diameter, flexible, chimney-like tubes on the mud surface. Although the expanse of tide flat looked homogeneous to us at first, once we start sampling, we find that the different worm types are quite distinctly zoned, with acorn worms, lugworms, and clam worms all found in slightly different tide heights and different textures of mud. We just haven’t found the parchment tube neighborhood yet. Then, from behind me, Reyn asks quietly, “Is this a parchment tubeworm?” It sure is! He shows me a six-inch worm, Chaet
opteris variopedatus, encased in a soft brown parchment tube.

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  Finding that delicate, rather exotic-looking worm in the mud of my native New Hampshire reminds me of my most thrilling worm sighting. David Brown and I were on a night dive off a remote shore in Wakatobi, Indonesia. The dive had not started well. We were picked up on a dark, windy beach, having signaled to a small boat with our lights, as if for a clandestine drug deal. Our captain then gunned the boat out through the surf, racing in the dark for a familiar gap between two small, rocky islands. Suddenly, our boat jolted to a stop. Someone had set a net across the gap, and our engine was ensnared. The captain and our dive guide, Jardeen, cursing in the dark, struggled to free the engine before the wind and breaking waves tossed us onto the nearby rocks. Finally, Jardeen jumped over the side and cut us loose. With what seemed like only feet to spare before hitting the rocks, the engine roared to life and we were on our way to dock with the mother ship, Patuno, which would serve as our dive platform. Once we were geared up and underwater, it still wasn’t going well: the seas were rough, a bit murky, and the site was either dynamited or storm tossed. We made our way across a shallow slope, weaving among a mixed jumble of overturned coral heads.

  There was a current moving us along, and captured in the beam of our flashlights were all the usual suspects: colorful fish and anemones, lionfish leering from ledges, crabs scuttling around the broken coral, and a lot of sand in between coral heads—a sign that coral cover was low on this impacted site. Suddenly, it got vastly better. Above the damaged coral, our lights picked up hundreds of foot-long animals undulating in the water like party streamers, swimming above the reef. Then we were in the middle of it, engulfed in an explosion of these streamers, jetting chaotically from reef to surface. I knew in a second of absolute wonder that these must be the mythic palolo worms. I would not have dared dream that we could be so lucky. We were caught in the middle of a huge spawning aggregation of these worms. Being in the middle of this felt like being in the etching by M.J. Schleiden (from Das Meer) where the ocean is dominated by every type of worm, including the swimming palolo, with weirdly metamorphosed segments. Palolo worms normally live quiet lives sequestered in branched burrows in the bottom sand. Most of the time, they look like an earthworm, a smooth-bodied worm with only small bristles on each segment, used to grip into their burrows. During their reproductive season, they make a dramatic metamorphosis to a large paddled swimming worm called an epitoke. Driven by hormonal changes and precise environmental cues, including the full moon, they swim toward the water surface. Then the gametes explode from their bodies to create a soup of swimming sperm seeking out ripe eggs. It’s not life’s end for each swimming palolo worm, because it left its head behind in the burrow to regenerate a new tail. But it is the beginning of the next generation of baby worms. David was beside himself with joy, filming the streamers, lit chaotically by his bright lights. I couldn’t wait to get back to my Blaschka collection and check to find if we actually had a palolo worm, since I had never imagined we’d have the luck to run into a spawning aggregation like this. Sure enough, the Blaschkas are always ahead of me and I found the worm watercolor in the Rakow Library at the Corning Museum, its modest form in watercolor belying its spectacular biology.

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  Understanding how worms are faring in today’s oceans is what we call a knowledge gap. For one thing, it is hard to keep track of the myriad name changes in all the invertebrate groups, but I certainly had the most difficult time updating species names with this group. Scientists must have the correct scientific name to be able to follow the fate of any species. Not only have over a third of the species names changed since the Blaschkas created their models, but it feels like a third of the species names I learned as a graduate student have also changed. In addition, there are only a few studies showing how any worms are affected by warming or other climate factors. Sally Woodin has studied changes in worm distributions in Europe and the Pacific Northwest. She had her start as a graduate student right outside my front door, studying worms in the tide flats of False Bay, on San Juan Island. More recently, she studied a common species of subtropical lugworm (Arenicola sp.) in Europe that is expanding its range northward with warming. The lugworm Arenicola sp. is a boreal species that is disappearing from the southern part of its range in Portugal and is increasingly rare in the Spanish Bay of Biscay (Wethey and Woodin 2008; Wethey et al. 2011). It is particularly sensitive to warming because newly recruited juvenile worms are killed by high temperatures on low summer tides.

  What about impacts from ocean acidification? There are large groups of worms, like the clam worms, that freely spawn their eggs and sperm, and those from locations like the Pacific Northwest that are impacted now by great upwellings of acidic, corrosive water may suffer reduced fertilization success. Many worms, for example the lugworms, also lay egg cases in their burrows, in which tiny embryos develop into swimming or crawling larvae. We will likely soon have research that will tell us what to expect for acidification impacts to these potentially vulnerable egg cases.

  It is hard for biologists to track and identify what is causing silent shifts under the mud. It will matter. Although worms are often unseen and seem quiet, they dominate soft sediment bays and play a large role in the economy of this shore. Some marine worms are just like earthworms and seagrasses in that they function as ecosystem engineers. Ecosystem engineers are species that create, modify, or maintain habitats for other species and thereby amplify biodiversity. Some engineers, like the lugworm, bioturbate, processing miles of mud and, in so doing, bring surface oxygen and organic rich sediment to deeper anoxic layers. Others, like the sand mason worm (Lanice conchilega), are stabilizers, preventing sediment erosion and increasing refugia from predators, much like seagrasses do (Woodin 1978, 1981).

  One of Cornell’s most beautiful glass pieces, the tubeworm (Pista cretacea) with the bright red gills, is related to the sand mason worm, which forms large reefs stabilized by its tubes (Godet et al. 2011). One of the largest of these reefs in Europe is in the bay of Mont Saint-Michel in France, a vast sandy bay governed by large tidal currents. The sand mason reefs are distinctive enough to be mappable by aerial photography and in 2002 covered an area of approximately 475 acres, which is just over half the size of Central Park in New York City. In this huge area, there are densities of 6,700 worms per square meter (Godet et al. 2011). That is a lot of worms, and they have a huge ecological impact in that they both churn up organic material and stabilize the sediments. They’re a conservation concern because of their importance and their vulnerability to coastal disturbance.

  Another favorite glass piece, Serpula vermicularis (page 84), is also considered an ecosystem engineer (ten Hove and van den Hurk 1993). In Loch Creran, Scotland, the intertwining tubes of Serpula form small, hard, connected reefs that can be a foot and a half tall and almost two feet wide. Serpulid reefs in shifting muddy bays form vital stable habitat for other species, such as the 276 taxa that were identified from ten reefs in the marine protected area of Loch Creran. Serpulid reefs have been identified as a priority habitat by the UK government’s Biodiversity Action Plan (Chapman et al. 2012).

  Worms are also an important food source in the economy of our oceans and in some cultures. Most commercial fisheries of the world are based on fish that rely on worms for food. Worms are the link that can turn poor-quality food, like mud, into valuable human food, like fish. Worms are even a direct food source in some cultures. For example, the palolo worm spawning aggregations are a huge protein source and delicacy for Samoans, who track the lunar-phased spawning and go out on dark nights to harvest the egg-laden worms.

  Worm-like invertebrates cover a large swath of invertebrate diversity (annelids, nemerteans, nematomorphs, nematodes, platyhelminthes, priapulids, and molluscs—shipworms and vermetid gastropods), but in spite of the evolutionary success of their body plan, they are relatively understudied (Fisher et al. 2011). Segmented worms, the annelids, ar
e currently the most diverse of the vermiform phyla, and annelids follow arthropods, molluscs, and fish in numbers of total species described by scientists (Warwick and Somerfield 2008; Costello et al. 2010). The International Union for Conservation of Nature is attempting to catalogue the global biodiversity of spineless animals. Currently, the likelihood of our detecting a problem in invertebrate biodiversity is 20 percent, compared to 80 percent for ray-finned fishes (Fisher et al. 2000). We have a problem with how little we know about conserving this component of biodiversity that lives right in our watery front yards. This is not something that requires rocket science; 160 years ago, the Blaschkas recognized and celebrated the central importance, the diversity, and the wonder of worms, yet to this day we have not figured out how to catalogue their changes in biodiversity.