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

Last month, 82 Green sea turtles hatched at SeaWorld in San Diego, California.

The eggs hatched on Shipwreck Beach and the youngsters didn’t need any human aid to get out of their shells and into the water. The park had decided to let nature take its course by refraining from incubating the eggs or help the hatchlings emerge. SeaWorld are now planning to dig up the beach to check if any buried eggs failed to hatch.

At the moment, the baby sea turtles are roughly one month old and only weigh a few grams. They happily feed on squid, shrimp, krill and special pellets. Assistant curator of fishes Tim Downing says they are all in excellent health and that they will go on display before the end of the year.

“There is so much that is not known about sea turtles,” said Downing. “We are getting real good information on the growth rate of juveniles. They are all gaining weight and doing well. We have done some X-rays, and they are progressing just like we would expect them to.”

SeaWorld is home to 30 adult sea turtles, including four Green sea turtles – three females and one male. They have been living at SeaWorld since the 1960s and are sexually mature, so all three females may have buried eggs in the sand. Only genetic testing will be able to reveal the maternity of each baby turtle.

All seven species of sea turtle in the world are endangered or threatened, with the Green sea turtle being listed as Endangered on the IUCN Red List of Threatened Species. It will be up to the National Marine Fisheries Service and the U.S. Fish and Wildlife Service to determine whether the new turtles will stay at SeaWorld and whether the adult turtles will be given opportunity to mate again next year.