The Ruination of the Ship:

Shipworms and their Impact on Human Maritime Travel

Trevor Hoberty

Wittenberg University

Marine Science Honors Thesis

Spring 2020

Thesis Committee: Dr. J. Welch, Advisor; Dr. K. Reinsel, 2nd Reader; Dr. M. Mattison, 3rd

Reader Hoberty 2

Abstract

Shipworms, family Teredinidae, are woodboring mollusks that have evolved specialized feeding strategies to glean nutrients from the consumption of wood. Through this feeding strategy, with the assistance of symbiotic Teredinibacter bacteria in the gut, the shipworm breaks down structurally dense wood in the marine ecosystem – introducing previously stored energy back into the system. Historically, this wood consumption has proved disastrous for human seafaring efforts. The destruction caused by means of shipworm feeding is heavily referenced in the historical record from the ancient to modern periods. Most all sailors or marine builders have faced disastrous damage because of the shipworm. Despite the tumultuous relationship present between the shipworm and humanity, this simple clam continues to fascinate researchers across the world.

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Introduction

The vessel though her mast be firm,

Beneath her copper bears a worm…

Far from New England’s blustering shores,

New England’s worm her hulk shall bore,

And sink her in the Indian seas,

Twine, wine, and hides, and China teas.1

(Thoreau)

As illustrated by these bars, and others throughout the written humanities, humans have long held a close connection to the ocean. From the gift of countless resources to an effective means of travel and commerce, the ocean has captivated our collective culture. However, the most interesting reference in this poem is not in regards to robust international trade. Instead, perhaps the most peculiar reference lies with a “worm” – a shipworm. The shipworm, a colloquial misnomer, is a woodboring marine bivalve mollusk of the family Teredinidae.

Occupying a masterfully evolved niche of the marine world, the Teredinidae have long plagued human efforts in the ocean. While often forgotten in our modern world, the shipworm remains as both a fascinating organism and a symbol of persistence in the natural world.

This endeavor explores the specialized biological life strategies of the shipworm, member of the family Teredinidae, within their wooden niche of the ocean ecosystem. These shipworms demonstrate an adaptive presence of feeding and survival, developed long before recorded time, that has long brought ruin to human efforts of maritime travel and exploration. In highlighting

1 Excerpt from Though all the Fates by Henry David Thoreau Hoberty 4 this interconnectivity, this paper will work to show the direct connections between this intricate biology and rich history, both persisting throughout the ages. A true interconnectivity that, like many secrets of the ocean, has began to show the potential to benefit modern industries – both medical and beyond.

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Chapter 1: Biology of the Shipworm

The shipworm is a truly specialized marine organism. Commonly referred to as the

“termites of the sea,” shipworms have developed a specialized feeding strategy that allows them to sustain themselves on both nutrients from the water column and the wood in which they live

(Cobb 2002). This unique feeding methodology has allowed the shipworm to carve out a significant niche in the marine ecosystem. This niche, centering around the management of wood in the ocean, has functioned to both manage an important ecological good and draw the distain of human seafarers throughout history (Cobb 2002; Masser and Sedell 1994).

Shipworm Larval Biology and Lifecyle

Shipworms, through their specialized feeding process, actively destroy the wooden habitat in which they live. As such, the organism must effectively reproduce and disperse offspring to new areas of available habitat (MacIntosh et al. 2014). In order to manage this, shipworms are selective in their reproductive strategies. These selective processes largely vary among differing species of shipworm. For example, members of the genus Bankia are more rapid in their means of reproduction. This species, and the majority of the Teredinidae, reproduce through oviparous means – projecting gametes into the water and allowing for external fertilization. In this method, a lengthy larval period of more than 20 days follows this fertilization event (MacIntosh et al. 2014). However, some species, such as Teredo, are more labor intensive with regard to reproduction. These species are larviparous – brooding eggs within the mantle cavity (MacIntosh et al. 2014). This brooding allows for further developed larva at the time of dispersal. Interestingly, these species, reaching sexual maturity around the eight-week mark, are able to invert their sex in order to create a more balanced population (Grave 1942).

This sexual inversion works to keep the community from becoming overpopulated with one Hoberty 6 given sex. Regardless of the reproductive method, newly developed shipworm larvae are promptly left free-swimming in the water column and tasked with finding an appropriate place of settlement.

As with many young marine invertebrates, these newly formed shipworm larvae are dependent on the physical workings of the ocean to find and colonize new areas. These organisms are able to achieve this goal through the effective use of ocean currents (Scheltema

1971). It has been found that the natural global circulation patterns of the ocean, coupled with the relative hardiness of the species as a whole, have allowed the transport of shipworm larvae across large distances. In fact, this successful larval transport has been hypothesized to be a driving factor behind the global distribution of the Teredinidae (Scheltema 1971). However, it must be noted that this successful transport is limited to those species that have longer phytoplanktotrophic life stages. These species, typically those of the oviparous variety, are able to remain pelagic for longer periods of time – moving farther distances with the current

(Scheltema 1971; MacIntosh et al. 2014). For species lacking this long pelagic phase, dispersal is much more limited. As a result, these organisms, more developed after being brooded in the body of the parent, are able to settle more quickly and wherever possible (Scheltema 1971).

Dominated by these factors, the larval stage of the shipworm can last anywhere from mere minutes to extended months (Toth et al. 2015).

In both instances, larva remain in the water column until they are prompted to settle through environmental cues. The most direct of these settlement cues proves to be presence of wood. It has long been hypothesized that shipworm larvae settle in response to chemical cues emitted by wood. In an experiment conducted by Toth et al. (2015), this hypothesis was tested by examining the settlement of shipworm larvae on covered and exposed pieces of wood. In all, it Hoberty 7 was found that larvae were more likely to settle in fresh, exposed wood substrates. Furthermore, larvae were more likely to settle in fresh wood adjacent to already invaded samples (Toth et al.

2015). While the exact compounds are not yet known, this experiment suggests that larval settlement is impacted by chemical factors. Once this appropriate wood habitat is found the shipworm larvae need only the smallest of holes to begin infestation (Cobb 2002). Once embedded in the wood, the bivalve is able to grow and feed from the safety of its burrow.

Shipworm Diversity and Anatomy

Within the family Teredinidae, there are approximately 65 recognized species across the globe (Turner 1966). Found in virtually all non-artic waters, the shipworm has long been championed for their resilience to changing environmental factors and physical conditions. For example, Teredo navilis, the common naval shipworm, has been known to tolerate temperatures ranging from 0 to 30℃ and salinity levels between 7-39 ppt (Borges et al. 2014).

Such resilience can be attributed to the specialized anatomy of the organism. The shipworm has a specialized body structure morphologically distinct from their bivalve relatives (Figure 1). Most notably, particularly in reference to other bivalves, the shipworm presents Figure 1: Physical Anatomy of the Shipworm a greatly reduced hinge and shell https://poi-australia.com.au/teredo-navalis-termites-of-the-sea-ship-worm/

(Turner 1966). This notched shell, found at the most posterior portion of the animal, is used as a rasp to bore into wooden substrates rather than a supportive structure (Dame 2012). Also located Hoberty 8 at this posterior end is a truncated foot and a well-developed system of adductor muscles (Turner

1966). These muscular structures work to aid in wood boring and anchors the organism within its burrow (Turner 1966). Moving along the anatomy of the shipworm, the body cavity of the animal is made of a largely closed mantle that houses the important internal anatomy. This cavity holds the majority of the feeding structures of the shipworm such as the gills and digestive organs (Turner 1966). The anterior portion of the shipworm boasts two relatively short siphons that can be extended outside of the wooden burrow. Interestingly, the shipworm lives their lives in these wooden burrows. In this intricate dynamic, the wood acts as both a food source and a habitat for the organism (MacIntosh et al. 2014). As such, the shipworm is forced to balance its feeding and other life processes with the continual self-destruction of habitat. With these characteristics, the family Teredinidae is truly unique.

Shipworm Feeding Biology

Once the larval organism is fully settled, the shipworm is able to dedicate its energy to a more important and specialized life process– feeding. Unique to the shipworm is the twofold feeding methodology in which it engages. The most simple of these methodologies, suspension filter feeding, works to mechanically remove nutritionally valuable seston from the water. The second of these feeding strategies, wood consumption, encompasses an intricate biological process that melds adaptive physiology and unique ecological symbiosis with the intricacies of molecular digestion. In order to understand the full scope of this feeding biology, each of these methods must be clearly defined.

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Filter Feeding

Of these feeding methods used by the shipworm, the most basic process is that of filter feeding. In this feeding method, the shipworm extends its siphons outside of its wooden burrow and into the open water (Figure 1). Once in position, the clam is able to draw in water through the incurrent siphon by means of cilia motion on the gills. Inside the body, this water is passed over the gills located in the closed mantle cavity. Here, mucus on the gills works to trap any planktonic food present in the water. Once trapped, the cilia of the gills work to transport these particles to the digestive tract where the organism can ingest the captured food. With these food stuffs effectively extracted from the water, the shipworm then expels this excess water, along with any waste material, out through the excurrent siphon. (Turner 1966).

Wood Consumption

The consumption of wood is a truly specialized feeding method used by the Teredinidae.

The process of wood feeding begins with simple means as the shipworm burrows in their wooden home. As the shipworm bores into the wood, the rough shell and powerful foot unique to the species is used as a rasp to wear away the structure (Turner 1966; Figure 1). In this process, ridged, “toothlike” structure on the hinge of the shell grind the wood into an incredibly fine powder. This finely milled wood is then taken into the mouth of the shipworm, located at the posterior end of the animal and beneath the shell (Turner 1966; O’Connor et al. 2014). Once consumed, the wood material is then transported to the gut to await chemical digestion. While effectively consumed by the organism, it must be noted that the wood molecule itself is still fully intact and ridged in nature (O’Connor et al. 2014). That said, the question centering around the workings of this digestion remains. Luckily, research has began to shed light on these fascinating process of shipworm digestion. Hoberty 10

Historic Timeline of Discovery

These questions of shipworm feeding and digestion have long worked to puzzle researchers. Since the initial documentation of the species in the early 18th century, people have attempted to understand this process (Turner 1966). At the surface level, shipworm feeding is simple. Since these early days, interested parties have been able to clearly observe the process of filter feeding as the shipworm extends its siphons outside of the secure burrow (Paalvast and

Velde 2103). However, the working of wood consumption proved to be a more challenging process to understand. It had long been hypothesized that shipworms, during the boring process, consumed some of the wood they actively live in (Pechenix et al. 1979). Many of these earlier experiments worked to prove that shipworms are able to sustain themselves on more than the nutrients received from filter feeding (Pechenix et al. 1979). The first major breakthrough in this understanding came in with the publication of the 1983 article by Waterbury, Calloway, and

Turner entitled “A Cellular Nitrogen-Fixing Bacterium Cultured from the Gland of Dedhayes In

Shipworms.” This article, published in the renowned journal Science, was the first documented explanation of how the shipworm digests its wooden diet (Waterbury et al. 1983).

In this now famous experiment, Waterbury, Calloway, and Turner, in looking at six different spices of shipworm, were able to culture morphologically similar bacteria from all individuals examined (Waterbury et al. 1983). These bacteria were cultured from the Gland of

Deshayes, a small organ unique to the Teredinidae located in the afferent brachial vein of gill

(Figure 2). The presence of this bacteria in the same organ of all subjects, collected from different areas, suggested that some type of symbiosis was present between the two organisms – a marine relationship unique to the shipworm (Waterbury et al. 1983). In this relationship, the bacterium benefits from the presence of a host in which to live. The shipworm, also benefiting Hoberty 11 from the relationship, is aided by the biological processes done by these bacteria. These impacts seemed to be twofold. First, the bacteria are able to secrete specialized enzymes that can be used in the proper digestion of wood. Second, the bacteria undergo the process of nitrogen fixation – a function that works to further supplement shipworm nutrition (Waterbury et al. 1983).

This discovery by Waterbury, Calloway, and Turner revolutionized our collective understanding of the diet and feeding methods of the shipworm. In the years since the discovery, research has largely shifted toward efforts to understand which of these feeding methods function as the primary means of sustenance. While definitive answers have not been made, this reliance on these differing feeding strategies seems to vary from species to species (Paalvast and

Velde 2013; Charles et al. 2018). For example, while Teredo navilis may rely on filter feeding as its primary means of nutrition, Bankia carinata thrives on a diet consisting of heightened wood content (Charles et al. 2018). While feeding methods are not uniform among species, the bacterium discovered by Waterbury, Calloway, and Turner remains an incredible discovery.

Teredinibacter

Since 1983, the shipworm bacterium has gained notable attention from researchers hoping to unlock the secrets of the organisms. The

Waterbury, Calloway, and Turner bacterium has since been classified as the Teredinibacter, named after the

Teredinidae family with whom its Figure 2: Microscopic view of the shipworm gill chamber showing the presence of Teredinibacter bacteria. (O'Connor et al., 2014)) symbiosis exists (Brito et al. 2018). The Hoberty 12

Teredinibacter is a gamma-proteobacterium and is gram negative. Surviving best at moderate temperatures and salinities, these bacteria are well suited to life within the body of the shipworm

(Brito et al. 2018). In fact, recent experiments have found these bacteria within the fertilized eggs of shipworms, suggesting that this symbiotic relationship is present from birth (Brito et al. 2018).

Of the several species of Teredinibacter, the most clearly studied is Teredinibacter turnerae.

Named in honor of the famous marine biologist Dr. Ruth Dixon Turner, of the research group

Waterbury, Calloway, and Turner, T. turnerae is found most numerously in the Teredinidae family (O’Connor et al. 2014). Most unique to this organism is the complex genome that allows for the production of wood degradation enzymes. Only recently mapped, “the complete genome of one strain of T. turnerae…revealed an arsenal of enzymes specialized in breaking down woody material” (Brito et al. 2018). With this mapped genome, the data further confirms that these bacteria are critical in the digestion of wood – a task not easily met by many organisms.

Wood Digestion

Wood is a natural substance rarely thought of as a food source. This lack of consumption can largely be attributed to the chemical nature of wood. Characteristically, wood is strong and ridged material that is not easily broken down. This rigid structure, making wood a useful building material, is around 75% carbohydrate by composition (Cote 1968). Of this carbohydrate, the majority of the substance is composed of cellulose and hemicellulose. These sugars are structured as a natural polymer – formed through powerful hydrogen bonds. Coupled with the dense cell wall of the wood molecule, these polymers give the molecule incredible strength (Cote 1968). As a result of this biochemistry, wood is a distinctly difficult substance to digest. However, with the help of the Teredinibacter, shipworms are uniquely positioned to achieve this goal. Hoberty 13

As stated, the Teredinibacter are initially found in the Gland of Deshayes, located in the lining of the gill chamber (Waterbury et al. 1983). As the animal filter feeds, catching and transporting water born nutrients from the gill to the gut, these bacteria become caught up in the feeding process. As a result, the bacteria are transported to the gut of the animal where the digestion of wood takes place (Greene and Freer

1986). In the gut, the final collection place for the wood Figure 3: Biochemical Structure of Wood. https://www.vectorstock.com/royalty-free- vector/cellulose-polymer-molecule-vector-4765968 particles consumed during boring, the Teredinibacter secrete wood degradation enzymes. In particular, these specialized bacteria are able to secrete cellulase (Cobb 2002). Cellulase, the enzyme specifically useful in degrading cellulose, works to destroy the rigid wood molecule (Sipe et al 2000). Once the cellulose polymer is compromised, the shipworm is able to digest the sugar and absorb the nutrients present within the wood.

However, this wood sugar, even coupled with other nutrients taken in through filter feeding, is not enough to fulfil the complete nutritional needs of the shipworm.

Nitrogen Fixation

Another key aspect of the Teredinidae and Teredinibacter symbiosis is the ability of the bacterium to undergo nitrogen fixation (Waterbury et al. 1983). In this relationship, the

Teredinibacter functions as a chemoheterotroph – producing nutrients from the chemicals in the surrounding environment. Here, the bacterium fixes both combined and molecular nitrogen from sea water into organic nitrogen (Waterbury et al. 1983). The production of this organic nitrogen is then used by the shipworm to fulfill the nutrient demands of the animal. In this case, this Hoberty 14 nitrogenous resource is used to construct basic amino acid chains that provide the animal with simple proteins (Cobb 2002). These simple proteins, coupled with the sugars digested from the consumed wood and the materials consumed through filter feeding, provide the shipworm with the complete nutrition needed for survival.

Ecology of Wood

Beyond providing the nutritional needs of the organism, the complex feeding methodology of the shipworm also plays an important role in the larger marine ecosystem. On land, wood, whether functioning as a living plant or environmental good, dominates in the form of expansive forests. However, once fallen, this wood is subject to the transportive powers of nature. Depending on the place of its downfall, this wood has the potential to be transported over large distances. For example, if this terrestrial wood were to enter a stream or river, the moving current of the water would transport the buoyant material to a larger body of water downstream.

Dependent on the power of this moving water, and the relative lack of blockages, this wood has the ability to journey all the way to the ocean environment. Once in the oceans, this wood is a significant natural resource (Maser and Sedell 1994). In the marine world, terrestrial driftwood provides protective cover for a rich diversity of small fish and invertebrate organisms. These areas of cover yield rich communities of varying organisms.

While this wood is an ecologically beneficial to the marine ecosystem, the overabundance of wood can prove to be harmful to ocean life. In all, the majority of floating debris in the ocean is plant material – namely wood (Maser and Sedell 1994). As such, the specialized feeding methodology of the shipworm works to lessen this environmental burden. As the shipworm bores into wood and feeds, the wood is readily deteriorated (MacIntosh et al. Hoberty 15

2014). In doing this, the shipworm functions as a detritus feeder that actively works to clear the oceans of this waste debris.

In all, the shipworm is a biologically complex organism that, through intricate specialization and a fascinating symbiosis, are able to maintain an important niche in the marine ecosystem. With this complex life cycle of destructive feeding, shipworms clear wood from the ocean – a process that has long brought disaster to human made structures within the ocean environment.

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Chapter 2: Shipworms and Maritime Travel

Humanity has used the sea for both subsistence and transportation long before the annals of recorded history. According to maritime historian Lionel Casson, “in the very beginning men went down, not to the sea but to quiet waters, and not in ships but in any that would float”

(Casson 1991). This early affinity for the ocean was present in virtually all early societies that bordered the resource. While credit for the creation of the first “boat” is given to Egyptian peoples of the fourth millennium B.C., stories of skilled ancient mariners can be found in Greek,

Mesopotamia, and countless other sources – centering around the Mediterranean and beyond

(Casson 1991). While such accounts can differ significantly in both purpose and methodology, one factor remains consistent – wood. With this introduction of new wood sources, boats, into the marine ecosystem, these early mariners began a battle against the shipworm that has truly spanned the whole of history.

Historiography of Shipworms

Shipworms, or what we know as shipworms, have long appeared in the historical record.

The first know recorded reference to shipworms dates back to 350 B.C. as Greek philosophers described the organism as “a terrible plague for which the there was little remedy (Cobb 2002).

Later Greek philosopher and naturalist Theophrastus, a student of Plato, describes the dynamic bivalve as a “worm which corrupts wood in the seas.” (Potter 1878) By the Roman era, author of natural history Pliny writes of “a large-headed teredo which gnaws with teeth and lives with the seas.” (Potter 1878)

As people continued to investigate the natural world, our understanding of the shipworm expanded. In a landmark treatise, Gottfried Sellius (1733) demonstrated that the shipworms were Hoberty 17 in fact members of the phylum Mollusca as he outlined the basic anatomy of the animal (Turner

1966). As early scientists continued to study the problematic clam, several species were recorded and logged across the world. However, like many early classification efforts, problems arose from different naming mechanisms – a problem that has long made proper study of the shipworm a difficult task. It was not until 1758 that Linnaeus instituted the genus Teredo to describe the shipworm in the 10th edition of Systema Naturae (Turner 1966). With this distinction, new species of shipworms were slowly added into catalogs. The first complete monograph of the

Teredinidae was completed by Soweby in 1875 – logging nineteen species of shipworm (Turner

1966). As scientific surveys continued in places across the Pacific, notably in the Philippine

Islands, new descriptions and papers were shared among the scientific community. Eventually, the interest in the Teredo moved beyond simple classifications. By the close of the First World

War, extensive experiments were underway to better understand the fouling process generated by the shipworm lifecycle (Turner 1966). By the mid-twentieth century, much of the shipworm was known – ranging from reproduction to feeding biology. Scientists, such as Dr. Ruth Dixon

Turner (the proclaimed goddess of shipworms) and others, in their work, have tirelessly managed to unlock the secrets of the Teredo.

Human Interaction with Shipworms

With such a long stated history, human interactions with the Teredinidae have been expansive. Beginning in the ancient period, references to shipworms and other fouling organisms have been found in the writings of seafaring Egyptian and Phoenician communities. In order to prevent the fouling and weakening of their wooden vessels, these peoples would cover their boats with thick layers of wax to prevent larval settlement (Cobb 2002). While not entirely Hoberty 18 effective at preventing fouling, these early effort to combat the destruction put forth by shipworms continued throughout the ages.

Moving to the early classical period, the matter of shipworm fouling became a much more pressing issue. A true hallmark of both the Hellenistic and Roman world centered around domination of maritime resources. In the Mediterranean Sea alone, Greek, and subsequent

Roman, sailors were able to create extensive trade routes that fostered a sense of both connectivity and mobility that spanned the 965,300 square mile body of water (Leidwanger &

Knappett 2018). In fact, for many Mediterranean costal societies, virtual all communication, travel, and economic interactions were dependent on a masterful usage of the sea (Leidwanger &

Knappett 2018). With such a strong reliance on the sea, these Mediterranean communities were constantly at odds with the shipworm. As with earlier mariners, Greek and Roman sailors covered their boats with substances like pitch and tar to deter larval infestation (Cobb, 2002).

Furthermore, lead sheathing found on Roman shipwrecks suggest that some sailors took undertook further methods to protect and/or repair the hulls of vessels damaged by shipworms

(Steinmayer & Turfa 1996). However, while these methods were sufficient for slow merchant ships, the bulky nature of such fixes could not be applied to the swift warships of the

Mediterranean. Instead, these warships, often made of light fir timbers, were subjected to rigorous beaching schedules. Here, in order to prevent exposure to Teredinidae settlement and kill any settled organism, any ship not actively in use would be stored on shore. While the exact process of such beaching efforts is not known, the sheer force needed to move the large vessels has long drawn the admiration of researchers (Steinmayer & Turfa 1996). In all, these innovative approaches to shipworm management continued though the medieval period. Hoberty 19

With the onset of the age of exploration, the relationship between shipworms and humans only worsened. As European sailors began to explore the world’s oceans, numerous sailing efforts were ruined by the destruction of ships by means of shipworm infestations (Buschmann and Nolde 2018). In truth, the impact of the Teredo could be felt by even the most skilled sailing crew. For example, famed explorer Christopher Columbus, on his fourth voyage to the American continents embarking in 1502, lost three of his four ship fleet to shipworm (likely Teredo navilis) based damages (Gilman 2016). Despite serval attempts to beach and repair the ships, Columbus and his crew were eventually stranded on the island of Jamaica for six months (Dugard 2005).

Furthermore, it has been theorized that shipworm damages likely weakened the timbers of the infamous Spanish Armada – providing Britain with their 1588 defeat of the sea power (Gilman

2016). Some even speculate that the whaling ship Essex could have been weakened by shipworm infestations; thus, allowing the ship to be damaged by the whale that would inspire the famous

Melville novel (Gilman 2016). Even the skilled navigator and cartographer Captain James Cook lost a ship to shipworm feeding activity in his travels round the world (Dugard 2001). However, with these continued frustrations also came new combative measures against the shipworm.

Some sailors, keeping in a similar vein to those of the past, would cover the bottom of their vessels in any available blocking material – ranging from black tar and moss to calf skin and hair. Others would intentionally “cure” their ships in frigid or freshwater area to slowly kill off the infestation. Some would create doubled hulled ships with the false, outer hull exposed to the water and the true hull safely behind a protective barrier (Cobb 2002). Perhaps most famously, the British Navy, in the latter half of the 18th century, covered the bottom of their fleet in copper plating – working to both cover the wooden hull and release toxic chemicals that proved to be an Hoberty 20 effective shipworm deterrent (Cobb 2002). Regardless of these and other strategies, people remained subject to the destructive nature of the shipworm.

In truth, humanity’s struggles against the shipworm has continued well into the modern era. While the number of wooden vessels in the ocean has decreased in the wake of other, inorganic building materials, other wooden structures remain vulnerable to shipworm attacks.

Wooden docks, piers, and other constructions along costal areas have often been destroyed by shipworms. In fact, during the late nineteenth and early twentieth centuries the American coastline experienced an epidemic of shipworm “attacks” (Nelson 2015). While likely present in the Americas for many years, the first major discussion of shipworms, namely T. navalis, dates to the mid 1800’s. By this time, increased naval activities associated with the American Civil

War brought the shipworm to the forefront of costal conversations. For example, after

Confederate troops destroyed shipworm-weakened wooden navigational buoys off the coast of

Delaware, the U.S. Army Corps of Engineers were ordered to stop with the use of wood in such projects (Nelson 2015). By Reconstruction, the focus of much of the nation had shifted to the defense of costal infrastructure – a goal not easily achieved. Across the nation, wharves and piers, infested with shipworm colonies, began to fall into disarray. However, such problems were not exclusive to the United States. In one 1902 accident, occurring in Tampico, Mexico, wooden support beams of a populated coastal dock buckled – leading to an estimated death toll nearing sixty women and children (Nelson 2015). As described by the February 18, 1902 issue of the

Biloxi Daily Herald, the tragic accident was attributed to the “ravages of the Teredo” (Nelson

2015). Destructive events such as this became so common during this epidemic period, that the very word “Teredo” worked its way into the common lexicon of the early 20th century. As environmental historian Derek Nelson describes, “the word Teredo was synonymous with the Hoberty 21 term ‘unstoppable’, ‘furtive,’ and ‘collapse’ which writers found handy to express political, economic, and even racial dissatisfaction” (Nelson 2015). With the given popularity of the word, it is no surprise that crews digging the famed Panama Canal, when tasked with naming their steel drilling barge, quickly settled on the name “Teredo” (Nelson 2015). In essence, the shipworm had worked its way into multiple facts of daily life.

Despite this prominence, concerns with shipworms largely began to die out by the middle of the 20th century. This fall from grace is largely due to innovation in building material. With newfound interests in plastics and other artificial materials, fewer wooden structures were built to foster infestation. Those that were still made of wood were heavily treated by noxious chemical. These chemicals worked to slowly toxify the surrounding waters – killing fouling organisms before they could settle. In the United States, creosote and chromated copper arsenate

(CCA) were among the most popular chemicals used to treat wood. While effective, these chemicals are extremely toxic and harmful to the marine environment – leading to a CCA fade out by the year 2004 (Cobb 2002). Slowly, the shipworms, a once feared marine pest, largely faded from the minds of the masses.

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Chapter 3: Impact and Synthesis

As discussed, interactions between humans and the Teredinidae has persisted throughout

the ages. Each player, working to make the most

of the maritime ecosystem, have strongly

influenced the success of one another. For

humans, interactions with shipworms were

categorized by a continued struggle to maintain Figure 4: The use of new building materials for boats and other have limited modern interaction with shipworms (Nelson 2015) space in the marine world. As stated, countless

deterrent methods have been devised to limit shipworm damage (Cobb 2002). Such struggles

continued until wood was largely replaced as the predominant building material (Figure 4).

However, this relationship, while frustrating for humanity, has largely benefitted the

shipworm. Beyond the presence of new food sources in the water, human sailing activity has

aided in the global distribution of the shipworm. (Maser and Sedell, 1994). Simply put, as

humans have sailed from place to

place, so too have shipworms. Often

times, such global travel functioned

to move shipworms to new areas.

The most direct example of this is

that of Teredo navalis (Figure 5). T.

navalis, originally found in the Figure 5: Global distirubution of the naval shiporm Teredo navalis. http://depts.washington.edu/oldenlab/wordpress/wp- Mediterranean Sea, can now be found in content/uploads/2013/03/Teredo-navalis_Elam.pdf

numerous locations across the globe (Cobb, 2002). Thanks in large part to the organism’s unique Hoberty 23 tolerance to varying levels of salinity, T. navalis has become one of the most widespread shipworm species across the globe (Gilman 2016).

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Chapter 4: Shipworms Today

As alluded to, public interest and discussion of shipworms began to reach a lull by the mid-20th century. Despite this relative lull in public interest, research into these fascinating organisms was continued by a dedicated few throughout the remainder of the 1ast century

(Turner 1966). However, the past decade has shown a rightful resurgence of shipworms as both a research subject and a destructive cultural threat.

Evolving Research

While much is now known about the Teredinidae, thanks in large part to early pioneering researchers like Ruth Dixon Turner, a plethora of ongoing research continues to examine the shipworm. For example, transportation of marine borers, such as shipworms, has become a field of interest among biologists – particularly following the historic 2011 Japanese tsunami. When the 9.0 magnitude earthquake, and subsequent tsunami, struck Japan an enormous amount of debris and building material, particularly wood, was washed out to sea. Since that time researchers have tracked the movement of these materials throughout the Pacific Ocean. Such efforts have recorded over 300 unique species, shipworms included, transported thousands of miles clinging to this floating debris (Gilman 2016). However, the Teredinidae themselves are not the only subject to receive newfound attention.

In fact, the symbiotic Teredinibacter bacterium living within the shipworm has begun to draw stronger attention in recent years than its host. Interest in the bacterium is widespread – ranging from environmental to medical initiatives. For instance, with the ability of the

Teredinibacter to so easily breakdown cellulose polymers, research is underway to utilize the bacterium in the production of biofuels (Cobb 2002). Other ongoing work assert that the Hoberty 25

Teredinibacter may yield new a new source of antibiotic drug therapies – a valuable resource in the world of increased antibiotic resistance (Klein 2020). Despite these promising endeavors, both the Teredinidae and Teredinibacter can still prove to be a destructive force.

Modern Concerns

While not the devastating destructive force seen in the historical record, shipworms are still estimated to cause $1 billion dollars of annual damage worldwide (Cobb 2002). The bulk of these damages, unsurprisingly, come from manmade costal structures like piers. However, recent concerns have been voiced for largely forgotten structures under threat of shipworm attacks – shipwrecks. Often regarded as heritage sites, numerous shipwrecks from various historical periods rest in European and American waters. As shipworm activity has began to increase, some believing the change to be instigated by the warming waters of climate change, these historical sites run the risk of disappearing (Gregory et al. 2012). In truth, these concerns are not unwarranted. Many famous shipwrecks have already begun to fall victim to shipworm feeding.

For example, the Queen Anne’s Revenge, the famed flagship of Captain Edward Thache (better known colloquially as the pirate Blackbeard) has shown extensive damage from shipworm activity. Resting off the coast of Beaufort, North Carolina much of the exposed wood of the ship has been destroyed by the shipworm (Wilde-Ramsing and Carnes-McNaughton 2018). Even the most famous shipwreck of the modern era, the RMS Titanic, has not been spared from the impact of shipworms. While the body of the ocean liner was of a steel construction, dives to the shipwreck have documented shipworm activity within the teak decks of the famed ship (Cobb

2002). In order to combat the loss of these sites, active research is ongoing to find the best possible method of preservation (Gregory et al. 2012; Eriksen and Gregory 2016). The destructive nature of shipworms continues to frustrate the people of today. Hoberty 26

Conclusion

In conclusion, shipworms are a truly special organism within the marine ecosystem.

These mollusks, from the safety of a wooden burrow are able to feed, grow and reproduce with little interference from the outside world. Through these biological life processes, the shipworm is able to consume and harness the energy from wood – cleaning the ocean of debris in the process. However, the destructive nature of this biology has long put the shipworm at odds with humanity. Going as far back as the ancient period, the feeding processes of shipworms have brought ruin to human sea travel. Throughout the ages, no human efforts in the sea were untouched by the Teredo. Yet, with modern developments in building and preservation, the shipworm has transitioned from public enemy to engaged research subject. Overall, despite the rocky nature of the shared relationship, the shipworm has cemented its place as a testament of destruction and persistence within the world of maritime history.

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