CALLUM MCCADDEN – 2000 WORDS
One of the greatest parasites in all human history is now forgotten. Naval museums are full of triumph of how we bested the oceans; from perilous expeditions to massive cargo ships that backbone the globalised economy, a lot has changed. Many inventions are categorised and detailed, from the invention of waxed sails to the steamship. Yet one problem is seldom discussed, for it never truly was solved: shipworm.
Shipworm is a generic term that refers to many species, a family of creatures some 20 million years old (Hoppe, 2002). Most infamous, albeit barely today, is the species Teredo Navalis. Teredo Navalis (henceforth teredo), will make short work of wooden structures in its viable waters, capable of completely devouring wooden piles in weeks to months (Cohen, 2014; Nelson, 2016). The reputation of this species is so powerful that the term teredo is short-hand in the literature for the many species of shipworm (Nelson, 2016). In addition, shipworms are highly diverse and not all are categorised (Lee et al., 2019). Shipworms, generally, have blighted ships throughout history, being major issues for seafaring empires from the Egyptians to the British (Davy, 1824; Hoppe, 2002). Even today, shipworms create damages estimated at one billion US dollars a year (Cobb, 2002). However, shipworms have a complicated relationship with humans, antagonistic in some areas but beneficial in others – in some countries they are eaten as delicacies (Lee et al., 2019). This short paper will analyse the lifeworld of the shipworm from three environmental humanities perspectives. Firstly, the biological understanding of the shipworms’ lifeworld will be outlined. Secondly, the political ecology of the imperial seafaring past will be analysed, with the shipworm considered a more-than-human agent. Finally, the shipworm will be considered in the context of climate change literature, and its potential to alter the future.
The shipworm’s lifeworld:
Shipworms exist in saline conditions, between 5 °C and 30 °C, where they have access to wood for food (Paalvast and van der Velde, 2011). Brooding and spawning varieties exist; both reproduce in large numbers (MacIntosh et al., 2014). Importantly, shipworms are not worms at all, but molluscs, meaning they filter-feed on nutrients in the water (Hoppe, 2002). They bore down the grain of the wood with two small retractable siphons pointing out of their cavity as the only indication of their presence, one injecting and one ejecting water (Hoppe, 2002). As a result, any piece of wood can literally be riddled with shipworm, completely instable, and yet look fine to the eye (Nelson, 2016). This is the primary reason that the shipworm has been implicated in great disasters such as the dyke failures in the Netherlands and the failure of the Spanish Armada’s English invasion (Nelson, 2016).
These creatures occupy an incredible niche in the oceans, forming a symbiotic relationship with bacteria in order to thrive on a diet of wood – sometimes exclusively (Hoppe, 2002). The bacteria produce cellulase from the cellulose in wood which is used as energy by shipworms (they also fix nitrogen) (Waterbury et al., 1983). The uniqueness of these bacteria has gained attention from researchers hoping to use the bacteria for commercial purposes, from enriching cattle food to creating biofuels (Cobb, 2002). It is this bacteria relationship that has allowed shipworm species to evolve into different niches. Recently, a proposal for new genus and species Lithoreo abatanica was put forward on the grounds its rock boring and ingesting traits set this shipworm apart (Shipway et al., 2019). It is currently unknown whether this shipworm gains nutrition from the ingested rock, or that its gut bacteria provide all nutrients through the water the shipworm continues to filter (Shipway et al., 2019). Likewise, giant shipworms have been discovered in the Philippines that survive solely on the hydrogen sulphide rising from vents on the ocean floor – a unique evolution from their wood eating cousins (Distel et al., 2017). In all, shipworms are abundant in the world’s oceans and occupy ecologically significant niches responsible for breaking down materials that are not conventionally food for most animals.
Empire and shipworms:
Due to their woody appetite, shipworms have long frustrated imperial ambitions, creating a political force of nature that has held back plans of empire. Greek and Roman vessels used lead sheeting as an attempted deterrent for shipworms (Crippa and Borrelli, 2019). Lead fell out of fashion soon after, likely due to its expense, and for the next 1500 years the seabound were left with inefficient tactics involving regular waxing, tarring and the literal charring of the bottom of boats (Crippa and Borrelli, 2019; Hoppe, 2002). The efficacy of these tactics is contested (Cock, 2001; Gollasch et al., 2009; Hoppe, 2002). Other than this, taking boats to freezing waters, careening the boat for repairs (where the boat is tipped onto its side) or the use of drydocks, if available, were the best methods for preventing destruction by shipworm (Cock, 2001). This had to be done regularly due to the rapid action of shipworm. 16th century European explorers were hampered by shipworm, with whole voyages being stalled (Cobb, 2002). By the time the British Empire had ambitions in tropical waters, where shipworm thrives, the threat for merchant ships was greater than that of pirates (Hoppe, 2002). Vessels involved in the slave trade rerouted around known shipworm waters and certain areas were never colonised (Nelson, 2016). In this manner, much like yellow fever in Anim-Addo’s (2014) example, ship worms expressed a more-than-human geographic agency on the route masters of colonialization.
Conversely, despite the best efforts of avoidance, there is considerable belief that the flows of empire and the Atlantic slave trade were vital in moving shipworm around the world – particularly to colder European waters where they further frustrated imperial ambition (Nelson, 2016). Capable of surviving six weeks out of water, shipworms were observed to be reproducing in British waters for the first time mid-18th century (however it had been present in warmer European waters earlier) (Cock, 2001; Hoppe, 2002). At this point, the accepted norm was the creation of sacrificial outer hulls from cheap timber for the shipworm to eat (Cock, 2001). This still required regular replacing and would cause deforestation in British colonies to fuel the demand for cheap timber (Cock, 2001; Nelson, 2016). In response to the expanding issue of shipworm, copper sheeting was introduced in the British Navy as an effective deterrent (Cock, 2001). Copper corrodes in seawater, and thus prevents shipworm from taking hold due to the poisonous film produced (Cock, 2001). This effect was observed, but lack of understanding of copper and iron’s reaction in seawater (an electrolyte) prevented the British Admiralty from knowing why the new copper sheeting was causing the rapid deterioration of ships’ iron bolts (Cock, 2001; Davy, 1824). Shipworm was clearly a massive issue for Britain’s imperial navy, as the Admiralty decided to copper all their ships despite the known issues (Knight, 1973). The exact effect on history is difficult to calculate, but what is clear is that shipworm was an evidenced natural barrier that constrained imperial ambitions, and one that followed the flows of imperial shipping, even if its exact origin is unknown (Gollasch et al., 2009).
In the post-colonial era, shipworms continued to be a political agent in the projection of force over the ocean. In the 19th century, coppering was replaced with copper alloys and slowly paints replaced plating (Cobb, 2002). Metal ships, after the invention of the ironclad, although blighted by other biofouling, do not suffer from shipworm (Dafforn et al., 2011). Despite innovation, the establishment of the United States of America as a fledgling power in the 19th century was a constant battle against shipworm (Nelson, 2016). Teredo devoured new port infrastructure wholesale, became a known term with many (negative) meanings, became an advertising point for freshwater harbours and its reputation was even manipulated politically to advance agendas even in its absence (Nelson, 2016). Teredo, was a terrifying word (Nelson, 2016). Today, the imperial powers of the modern era are in a position of relative liberty from shipworm. However, less powerful and poorer countries still suffer under the blight of the shipworm, only exaggerating the power imbalance (Cobb, 2002). Poorer boat owners often work with wooden vessels and are unable to afford expensive biocidal paints (Cobb, 2002). Combine the fact that these people are often fishermen, and the paints used are highly toxic to the environment, prevention of shipworm can be multifaceted and devastating (Cobb, 2002). Shipworms are powerful because of their longevity, even surviving long ocean voyages after the Japanese 2011 tsunami creating a potential invasive species threat for Hawaii (Treneman et al., 2018). Furthermore, the globalised movement of goods which is so often facilitated by capital coming from neo-imperial powers can actually move shipworm around the world, surviving in the ballast water of container ships (Cohen, 2004), although mediocre progress has been made by the ‘International Convention for the Control and Management of Ships’ Ballast Water and Sediments’ that entered into force in 2017 (IMO, 2020). As such, shipworms, along with other invasive species, continue to be a political agent in the world’s oceans.
Climate change and the future:
Due to anthropogenic climate change, the territory of shipworms is set to expand and through differing access to technology this reflects global inequality. Freshwater is a natural defence against shipworms, which need salinity to survive (Nelson, 2016). Resultantly, it is of considerable worry that climate change induced droughts could increase the salinity of estuary harbours and thus increase the habitat of shipworms (Paalvast and van der Velde, 2011). This specific example has been modelled in Rotterdam, where climate change leads to the scenario of teredo shipworm expanding upriver and destroying wooden structures (Paalvast and van der Velde, 2011). Furthermore, many countries have banned traditional biocides used to prevent shipworm, namely Creosote and Chromated Copper Arsenate (Cobb, 2002). These toxic substances are carcinogenic to their environments but without them wooden structures are vulnerable (Dafforn et al., 2011). There are alternatives such as the use of concrete (expensive; vulnerable to a different boring clam species), plastic structures (expensive; vulnerable to melting) and tropical timbers that cause deforestation issues (Cobb, 2002; Nelson, 2016). As such, Nelson’s (2016) contention that ‘for all intents and purposes, teredo is history’ is an incredibly bold one considering the habitat of shipworm is set to expand particularly into areas with wooden structures and that much of the world still uses wooden boats for their livelihoods (Cobb, 2002). Furthermore, a deep environmental perspective may consider wood as a more ecologically sustainable material against non-renewable metals. For example, most metal cargo ships going out of service are ‘broken’ at dangerously polluted coasts, particularly in Bangladesh and India (Hossain and Islam, 2006; Psaraftis, 2019). There are new shipping companies that have returned to wooden vessels such as Tres Hombres shipping and Sail Cargo (Sail Cargo, 2020; Tres Hombres, 2020). With that said these two examples are a drop in the ocean compared to the world’s 62,503, predominantly steel, cargo ships (Psaraftis, 2019). The ability to prevent expanding shipworm territories reflects and expands global inequalities, where cheaper measures are toxic and the alternatives expensive.
Conclusions:
Shipworms are an ecologically important, if relatively unknown, set of molluscs. They continue to inhibit human efforts in the oceans, particularly in countries with less financial capital. The deterrents used are either toxic in the case of chemicals, impractical as in plastics and concrete, or expensive and exhaustible as metals. Throughout history, and today, shipworms express a more than human agency on human efforts in the sea. Looking forward, shipworms are likely to be a bigger issue for human structures as their territory expands into spaces considered relatively safe. Considering the geographic implications of shipworm now could be useful in preventing the wholesale destruction of human structures without desperate last-minute application of biocides. In the uneven outcomes of a global issue, shipworms have come to represent many issues in our unsustainable global world, from colonial histories to unjust economic outcomes and the contested release of toxic pollutants into the natural world.
Word Count: 2000
All rights reserved to Callum McCadden. Originally submitted to the University of Edinburgh as coursework for ‘The Blue Humanities’ geography course, 2020. Later self-published in June 2021 via this website.
“Original Assignment: ‘Demonstrate how your understanding of an organism’s lifeworld is informed by conceptual approaches derived from the environmental humanities’.”
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