Category: Excellence in Environmental Journalism
Author: Henrik Kaufholz (Denmark)
“Shipworms are eating our heritage”
February 10, 2019
In Danish waters there is only metal left of the many ship wrecks. All wooden material has been eaten by 'the termites of the sea', which due to climate change are spreading eastwards along the German coast in the Baltic Sea. 100,000 well preserved ship wrecks are located here, and marine archaeologists are in despair: Shipworms have no natural enemies and the use of pesticides is prohibited.
The summer of 2018 was exceptionaily hot at the Baltic Sea. Hundreds of thousands of Germans, Swedes and Danes enjoyed bathing in the warm sea at all holiday resorts.
Also enjoying the warm water were shipworms, which over the past decades have spread slowly but relentlessly eastwards along the German coast.
Shipworms are also labelled 'termites of thesea' because they eat all wooden material they can find: bathing jetties, piers, groynes and last but not least ship wrecks.
This is of major concern for archaeologists and historians because at the bottom of the Baltic Sea there are approximately 100,000 well preserved wooden ship wrecks from the time of the Vikings to the present: "This is an invaluable treasure of heritage from which we can learn a lot about trade, war, shipbuilding, daily life on board and a lot of other things from many centuries," says the world-famous marine archaeologist, David Gregory, from the Danish National Museum's department of conservation in Brede north of Copenhagen.
Till now this treasure of wrecks of which probably 6,000 are of special interest to scientists have been lying peacefully at the bottom of the sea with no shipworms in sight. Shipworms are only able to live and reproduce in warm and salty water, where they also have enough oxygen. So, the Eastern part of the Baltic Sea has until now never seen attacks of shipworms - the water issimply too fresh, i.e. notsalty enough.
Warmer and warmer
But this is changing. Shipworms of the very aggressive species Terodo navalis are currently thriving in the saltier part of Danish, German and Swedish waters and are spreading eastwards. According to new scientific research the reason is climate change, concludes the German biologist. Dr. Heike Lippert from the University of Rostock.
Dr. Lippert is the only scientist in the whole Baltic region who is monitoring shipworms systematically. Her research is fmanced by the German State of Mecklenburg-Vorpommern. The State has a long coastline and over the last decades, it has renewed and repaired groynes at a cost of more than 33 million dollars.
According to Dr. Lippert's monitoring, the water at the German coast in the Baltic Sea in 2018 was warmer than ever registered before - 20.4 degrees centigrade. The water was almost as warm two summers earlier, in 2016, when she also registered a sudden growth in the population of shipworms.
"Our theory is that the shipworms are spreading eastwards because of the rising temperature of the sea water, and because of climate change this is a phenomenon we have to face and live with," says Heike Lippert.
"Over the last three years we have observed shipworms reproducing east of the island of Hiddensee, and they were found for first time along the island of Rugen in 2016. They have not yet reached the more eastward located island of Usedom, where we are also monitoring for shipworms."
"From time to time we find pieces of wood infested by shipworms far east of Rugen, but the water there is too fresh and cold for them to settie there on a permanent basis. So, they will die before they can do any harm."
Easy to find
In the German monitoring programme the scientists place small pieces of wood in 8 permanent monitoring stations. !f a shipworm passes by it will certainly settie and eat of the wood pieces, and all the biologists have to do is count the holes where the worms are living.
At 3 stations the biologists are also registering the temperature of the water and its salinity. Especially the latter requires a lot of work and checking because algae and other living organisms settie on the instruments and so they must be cleaned every week.
"The salinity variesa little during the summer, but the temperature-which is oneof the three most important living conditions for shipworms - is what is really changing at this time," says Heike Lippert. She adds that the marine environment changes quickly and because of that it is not possible to mark exactly how far east in the Baltic Sea the shipworms are now living.
"This depends on currents, salinity and temperature. But the trend over the last decade is quite clear: They are moving eastwards."
Shipworms are an old problem. Both the ancient Egyptians and Greeks - shipworms are mentioned by both Aristotle and Ovid - were fighting shipworms of which there are many different species in all oceans.
According to new Swedish archaeological findings, the Vikings produced tar and used it to protect their famous longships against shipworms.
During Columbus' fourth expedition 1502-03 the shipworms literally ate the frames away under the feet of the crews of the ships 'Gallega' and 'Vizcaina' and in the beginning of the 1730'ies they had pierced Dutch sea dikes, piers and lock gates to such an extent that they collapsed during floods and high tides. Several hundred people lost their lives.
A particuiarly violent attack happened almost 100 years ago in the USA. On a peaceful day in the autumn of 1920, the piers of the shipbuilding company Benica in San Francisco began to sway. Suddenly they collapsed. Trucks, equipment and building materials feil into the water. Finally, a customs Office also collapsed.
The shipbuilders were at a loss, because the collapse was not caused by one of the frequent earthquakes. But then what? In the following weeks more piers and ferry berths collapsed.
Chemists, biologists and engineers did find an explanation. The very solid wooden structures were pierced by shipworms. The balks were suddenly so soft that you could sink your nails into them, but the holes left by the shipworms are very small and you have to look very carefully to see them. So, nobody had noticed. The costs of repair works amounted to what would in our time be 15 billion dollars.
The bay at San Francisco was considered free of shipworms because of very low salinity. It was precisely for that reason that commander John Sloat of the US Navy decided to place a new base for his warships here "safe from wind, waves, the enemy and marine worms" as he stated in his order.
Commander Sloat feared the Pacific species of shipworms, Bankia setacea, which can only live in very saity waters. But the American navy officer did not take the cousin of Bankia, Teredo navalis, into account. Teredo is the most aggressive of all the species and has been found in all seven seas. And so, most of his port collapsed.
Wrecks are reburied
The Danish veteran diver Gert Normann Andersen who runs the company JD-Contractor and has also established the Sea War Museum in the town of Thyborøn knows first-hand how shipworms cause havoc: "When we dive in the North Sea, Skagerrak or Kattegat we find only the metal parts of the ships-all wooden material is gone. Every part made of wood has been eaten away unless it has been covered by sediment."
"When we find ships built of iron there are no decks, no doors, no lifeboats left. When we find new wooden wrecks there is usually only the engine, the anchor and other technical equipment left. The shipworms really finish their meal."
A few years ago the Swedish biologist Christin Appelqvist estimated that approximately 100 ship wrecks have been attacked by shipworms in the area between the German island of Rugen and the small Swedish town of Klagshamn in Scania, where shipworms have been registered in recent years.
This is of specific concern to Jens Auer, who is head of the marine archaeological department of the government of the State of Mecklenburg-Vorpommern and follows the monitering done by Dr. Lippert closely:
"We have a lot of wrecks along the coasts worthy of preservation and some of them lie exaetly east of Rugen, where Lippert is working. The shipworms have no natural enemies, so our only option is to bury the wrecks, cover them with tarpaulins and gravel and thus see that there is no oxygen for the shipworms. Without oxygen the shipworms will die," says Jens Auer who earlier in his career was associate professor at the University of Southern Denmark in Odense.
His colleague in the State of Schleswig-Holstein, Daniel Zwick, is also advocating the method of covering the wrecks and he is also active in the BalticRIM-project, which is working to improve planning procedures in coastal regions:
"But for covering to succeed you need fairly calm currents and wind conditions. My State also has a coastline in the North Sea, and there we really face the extreme powers of the weather and sea. A wreck can Ile deep under the bottom of the sea for many years and then suddenly appear after a storm," he says and points to the Hornum-wreck from 1690.
"Here the strong erosion is a much bigger problem for us than shipworms. In the year after the Hornumwreck rose to the surface, we could follow how the sea ate its way 10 meters into the coast in just two months. Because of that the wreck was splintered by the waves and spread by the tide. We had no other option than to just look at what happened."
Expensive to raise the wrecks
In Denmark the Agency for Palaces and Culture is responsible for underwater heritage in the seas around the kingdom, and the consultant working with the subject, Torben Malm, is also advocating the method of covering the wrecks to protect them against shipworms and general decay:
"This is not just about ship wrecks. We must also protect several valuable settlements from the stone age, which are today under water. In our waters, we really do have a lot of valuable heritage to protect against shipworms. We cannot take this heritage for granted any longer."
It is of course possible to save smaller parts of the wrecks, but "it would be almost prohibitive from a financial point of viewto raise the wrecks and exhibitthe wrecks as we have done at the Viking Ships Museum in Roskilde and the Vasa museum in Stockholm," Malm says.
Some ship wrecks and old settlements have been covered with a carpet of sand and gravel - a layer of between 1 and 2 meters.
"But we do not have money for diving to keep an eye on the situation of each ship or settlement. For this we have to rely on sports divers with whom we have developed a fairly good cooperation."
When unknown wrecks suddenly appear during construction of new ports, tunnels or bridges the agency sees that they are registered, examined and filmed. After that they are reburied. The cost of just one of these fairly simple operations runs into millions of dollars:
"This is a clear message about the financial dimensions of the management of the heritage at the bottom of the sea. Nobody advocates to raise just a few of the most valuable wrecks and UNESCO also recommends this so-called 'in situ' method of preservation," Malm says.
Notaworm at all
The shipworm, Teredo navalis, is actually not a worm at all, but a mussel or mollusk-a driliing one. And it is also not eating the wood itself.
"It is difficult to get shipworms out of the wood alive, so there is a lot we do not know about Teredo navalis yet," explains Heike Lippert.
"For one thing we do not know the origin. Nor do we know why they are more aggressive in some years than in others."
Shipworms - as they are still called by sailors and engineers - live in wood - the softer the better. Every individual lays from 50,000 to 2 million eggs. The larvae swim or are transported by currents for 30 days and are spread around in this way. When their threads feel wood the larvae at once fasten themselves and start drilling.
In Northern European waters they will usually grow to 20-30 centimeters long and 9-10 millimeters thick, but much larger individuals have been found in the Pacific Ocean.
The shipworm or drilling clam insulates its narrow corridor with chalk and is also able to shut the corridor to survivesudden changes of the environment-lack of oxygen or pollution-for 5 to 6 weeks. The drilling holes are tiny and as wooden piers and other wooden structures in seawater are covered by other organisms such as algae and seaweed, the attacks are usually not noticed until it is too late.
It drills its corridors with two small sharp plates which are also the classical way of identifying the species. The drilled material is turned into sugar by enzymes. These enzymes are produced by bacteria that live symbiotically with the mussel - they are notan organic part of the Teredo navalis itself.
Put a shipworm in your tank
At the US government's research facility Ocean Genome Legacy Center of New England Biolabs scientists have for years explored the digestion system of commander Sloat's enemy, Bankia setacea.
In a telephone interview the director of the center, Daniel Distel, tells Politiken "that here we have found a quite new way of breaking down biological material with a huge potential for the production of bio fuel."
"Most animals, including people, have beneficial bacteria in their digestive system to help them digest food and would quickly become sick and malnourished without them. But shipworms have no bacteria in the part of the gut where their food is digested. instead, they house symbiotic bacteria inside specialized cells in their giils, a location far removed from the gut," explains director Distel.
"No other animal in the world is known to rely on bacteria outside of its digestive system to produce its digestive enzymes and no other intraceliular bacterium is known to produce enzymes that function in the outside world of the host. This discovery can be used on an industrial scale, but we have not been able to find money for more research."
Shipworms have no natural enemies -other than man. Authorities in Denmark, Germany and Sweden cannot do much about these small drilling mussels but repair the damage. Clearly a Sisyphean task.
In Gothenburg in Sweden deputy manager Anders Soderberg from Grefab, which is managing all marinas in the region, estimates that his company is spending 35,000 dollars every year to replace posts damaged by shipworms.
"We have also tried to use Steel posts, but wooden posts are simply more appropriate in marinas," he explains in an e-mail.
Danish marinas have also learned a lesson or two. "Almost every Danish marina is reporting attacks by shipworms," says director Jesper Højenvang from the Organization of Danish Marinas. "We have no scientific research but judging by the reports from our members the attacks by shipworms are getting worse and worse."
It is a major problem for the port authorities that for the moment there are no approved pesticides to fight or protect against shipworms.
"The procedure to get a new remedy approved is very expensive and we very often get the expianation that the market for this is too small/' says consultant Søren Bank-Achton from the Danish Technological Institute.
"I have not heard of any firms which have products ready for the approval procedure."
"So, for the moment we recommend the use of tropical wood. We now know that shipworms find it very, very difficultto drill and live in tropical types of wood. But even if you use wood with certificates of sustainability, you must ask yourself if this is a good idea - just look at the carbon footprint of this wood. We have to import it from the other side of the globe. On top of this tropical wood comes in many different qualities."
More bad news
In the Netherlands where shipworms 300 years ago took hundreds of lives, the biologist Peter Paalvast from the Consulting company Ecoconsult has tried to look into the future. He does not like what he sees.
"New threats from an old enemy" is the headline of his report about the consequences of climate change for the Port of Rotterdam - the largest port in Europe.
"We have to expect that shipworms will swim 25 kilometers further up the Rhine than today. The reason is that with the rising sea levels more salty water than today will flow up the river. Also, we will have less rainfall in the hinterland due to higher temperatures," he says.
"As a consequence of climate change this problem will also hit other Northern European ports situated at rivers. According to brand new calculations this will be even worse in Southern Europe."
Captions, pages 21-22
Wormhunting. The German biologist Heike Lippert catch the 'termites of the sea' in traps, which she installs every year along the coast.
Favorite food. These small plates of wood is the favorite food of shipworms. Its therefor easy for the biologists to find out if there is attack of shipworms.
Captions, pages 23-24
Replacing. The Swedish city of Gothenburg has to use 35,000 dollars every year to replace wood attacked by shipworms.
Sharp jaws. The shipworms look innocent, but they are able to penetrate and spoil solid wood structures in a few years.
Treasure at the bottom
Approximately 100.000 well preserved ship wrecks are lying at the bottom of the Baltic Sea. Shipworms eating all wooden material on their way can due to climate change now spread to areas where used to die because of lack of oxygen.
Red dots: registered ship wrecks
Quote: The shipworms really finish their dinner
Gert Normann Andersen, diver