The shipworm Teredo navalis is spreading to the Baltic Sea, threatening to destroy archaeological artefacts. Researchers* at Gothenburg University suspect that climate change is what’s making it possible for this species to spread and are now joining the EU project WreckProtect, a cooperative effort to assess which archaeological treasures are at risk. The project includes researchers from Sweden, Denmark and the Netherlands, as well as experts from France and Germany.

Not really a worm
Shipworms are not actually worms but saltwater clams with much reduced shells. They are notorious for borrowing into and gradually destroying wooden structures in saltwater; earning the nickname “termites of the sea”.

There are 65 different know species of shipworm but Teredo navalis is the only one currently known to spread into the Baltic Sea via the Great Belt. Teredo navalis forms up to 30 cm deep tunnels in submerged wood and is difficult to detect since it remains hidden inside the tunnel. It has a life expectancy of 3-4 years.

Teredo navalis can survive in a salinity of 4-6 practical salinity unit (PSU) for short periods of time but can not reproduce unless the salinity is at least 8 PSU. The salinity of the Baltic Sea decrease the further north you get with the Stockholm Archipelago sporting an average salinity of roughly 5 PSU.

The shipworm is capable of completely destroying large maritime archaeological finds in only 10 years, and while it has avoided the Baltic Sea in the past, since it does not do well in low salinity water, it can now be spotted along both the Danish and German Baltic Sea coasts.

14th century shipwrecks under attack

“Wrecks that have been resting unharmed since the 14th century have now been attacked off the coast of Rügen in Germany, and we are also noticing attacks along the Swedish coast, including destruction of the Ribersborg cold bath house in Malmö,” says Christin Appelqvist, doctoral student at the Department of Marine Ecology, University of Gothenburg.

Appelqvist and her colleagues suspect that increased water temperatures may be helping the shipworm to tolerate a lower salinity.

One of the objectives of project WreckProtect is to develop methods for the preservation and protection of shipwrecks. It might for instance be possible to cover the wrecks with geotextile and bottom sediment.

100,000 wrecks may be at risk
Thanks to the absence of Teredo navalis there is currently around 100,000 well preserved shipwrecks resting in the Baltic Sea, a true treasure for historians and archaeologists. If the shipworm continues to spread these ships may vanish before anyone has a chance to explore them.

“Around 100 wrecks are already infested in the Southern Baltic, but yet it hasn’t even spread past Falsterbo. We know it can survive the salinity of the Stockholm archipelago, although it needs water with higher salinity than that to be able to reproduce,” says Appelqvist.

* Christin Appelqvist, Department of Marine Ecology, University of Gothenburg
http://www.marecol.gu.se/Personal/Christin_Appelqvist/

* Jon Havenhand, Department of Marine Ecology, University of Gothenburg
http://www.tmbl.gu.se/staff/JonHavenhand.html

Picture credit: http://www.science.gu.se

According to a new report jointly produced by UN Food and Agriculture Organisation (FAO) and UN Environment Programme (Unep), merchant ships are to blame for 88 percent of the total marine littering in the world. According to the report, merchant ships deposit 5.6 million tonnes of litter in the ocean each year.

About 8 million pieces of marine litter enters our oceans each day and most of it is solid waste thrown overboard or accidently lost from ships. Right now, an average of 13,000 pieces of plastic litter is floating around per square kilometre of ocean waters, the report says.

The FAO-Unep report has been released right before next weeks’ World Oceans Conference in Manado, Indonesia where marine littering will be high on the agenda.

A majority of the litter from ships is fishing gear, which is either lost or intentionally abandoned in the water. Fishing gear now accounts for one tenth of all marine litter.

The rest consists of various debris, such as shipping containers, pallets, plastic covers, drums, wires and ropes. Accumulated oils are also dumped by ships; oils which can cause serious injury to marine life.

“Most fishing gear is not deliberately discarded but is lost in storms or strong currents or from’ gear conflicts’”, the report states. “For example, fishing with nets in areas where bottom-traps that can entangle them are already deployed.”

Unfortunately, lost and abandoned fishing gear will not stop fishing – they will continue to trap animals until they are broken down; a process which can take many years since modern fishing gear are made from highly durable synthetic materials. This is referred to as ghost fishing and is a major problem for aquatic species that need to surface regularly to breathe; a dolphin, turtle or seal caught in a net will suffocate and die. Lost fishing gears are also a problem for ships that become entangled in the equipment and are known to damage boats and cause accidents at sea.

While the report points a finger at merchant vessels, it also states that land-based sources are the main cause of marine littering in coastal regions.

UN recommends financial incentives and new technology

The report recommends using financial incentives to encourage fishers to bring old and damaged gear to port instead of dumping it. Fishers should also be given incentives to bring ghost nets recovered while fishing back to shore and to log and report items lost at sea. For this to work disposal facilities must be set up in ports and a report and recovery system must be established. The report also suggests providing ships with oversized, high-strength disposal bags to place discarded fishing gear in.

“A ‘no-blame’ approach should be followed with respect to liability for losses, their impacts, and any recovery efforts,” the report says.

New technologies – such as seabed imaging, geographic Positioning Systems (GPS), and transponders – can be used locate where lost or dumped fishing gear is present and recover it. Fishing ships could use GPS to mark locations where objects have been lost and weather monitoring technology could be used to predict there the stuff will go. It is also possible to attach transponders to fishing gear, shipping containers and other types or property known to frequently get lost at sea.

Weather monitoring technology can also reduce the risk of property getting lost at sea by altering captains in advance, e.g. to prevent them from deploying nets when unusually severe weather is on its way.

The study also recommends speeding up the development and commercial adoption of durable but bio-degradable fishing gear, including gear containing magnetic solutions.

International Convention

Ichiro Nomura, FAO assistant director general for fisheries and aquaculture, has called for industry and governments to take action to radically reduce the amount of lost and abandoned fishing gear in the sea. If nothing is done, fishing gear will continue to accumulate in the world’s oceans and their impact on marine ecosystems will become more and more severe. Nomura stressed that the problem must be addressed on multiple fronts and include both littering prevention and restoration measures.

FAO is currently involved in an ongoing review of Annex V of the International Convention for the Prevention of Pollution from Ships (MARPOL) as regards fishing gear and shore side reception facilities by the International Maritime Organisation (IMO).