By Beate Hoddevik Sunnset
Genetic tests have also been carried out on the lobsters, revealing that both are American lobsters (Homarus americanus). This species are occasionally found in Nordic waters since 1999 and are believed to origin from live import of the species.
A further two dead American lobsters will also be tested. Both of them died after suffering similar damage to their shells whilst exhibited at the Drøbak and Risør aquariums. These lobsters were caught in Oslofjorden over the period 1999-2001, and their shells were not visibly damaged when they were caught. One of these survived until 2007.
Genetic, bacteriological and toxicological tests
Genetic tests have been done, confirming that all four are American. In order to determine whether the lobsters are suffering from the disease, samples are taken for bacteriological analysis. Also blood and tissue samples are to be screened for pathogens and probably also for pollutants. It will take some time to clarify whether the lobsters are suffering from the "new" disease.
Epizootic shell disease is a disease that results in the lobster's shell being eroded by organisms such as chitin-eating bacteria. The mortality rate depends on how badly the lobster is affected. The disease prompts lobsters to moult early; when this happens, berried lobsters lose all of their roe, although moulting can cure minor outbreaks of the disease. However, in the case of individuals that are already weakened, the new shell starts to erode again, often soon after moulting.
If the lobster is badly damaged at the time of moulting, this weakens the lobster and results in a higher mortality rate. If there is very serious shell damage, the remains of the shell stay attached to the underlying epidermis, preventing the lobster from replacing its shell. Damage has also been observed to the reproductive organs of very badly affected males.
However, this is not the case for females, and they are more susceptible to the disease. It is not known whether the disease reduces the overall population. In the most badly affected US states, 20 to 30% of the lobster population suffers from the disease.
Common in the US
In the US, the disease is particularly common in the southern part of the range of the American lobster. It is also found relatively often as far north as Massachusetts, whilst sporadic instances have been observed in Maine and Canadian waters. The disease was first discovered in individuals in the late 1980s. In 1999 the fishermen of Long Island Sound, north of New York, warned of an impending catastrophe. The disease has now made it impossible to catch lobster there.
Other areas where lobster fishing used to be a major industry, such as Connecticut and Rhode Island, are also badly affected.
Cause remains a mystery
If the four lobsters currently being tested have epizootic shell disease, it will be the first time that the disease has been observed in lobster in Europe. Scientists do not know what causes the disease. For the moment it is unclear what impact the disease might have on the European lobster (Homarus gammarus), but at the moment it is not even clear if it is infectious between lobsters.
Whatever it is causing the shell disease, it is not previously known in European waters. A possible outbreak in Norway must be taken seriously.