Are European lobsters under threat?

An American (top) and European (bottom) lobster. 

So, in my last blog post, I talked about how I recently published a paper, which I am obviously very excited about! It is in the Journal of Invertebrate Pathology and is a result of my recent collaboration with the team of Dr. Michael Tlusty at the New England Aquarium in Boston, one of the papers we were looking over whilst I visited back in October.

The study was funded by the Marine Management Organization’s Fisheries Challenge Fund with the stakeholder support of the Shellfish Association of Great Britain, plus some funding from another grant; the European Regional Development Fund (Interreg 4A, Ireland–Wales, 2007–2013, SUSFISH).

The aim was to assess the importation of live lobsters into the UK, in terms of disease transfer to European lobsters (Homarus gammarus). More and more, American lobsters (H. americanus) are being found in European waters, which have been documented by fishermen, most actively around Norweigan waters (Stebbing et al., 2003; Jørstad et al., 2011).

When I was out in Charlottetown, PEI, Adam told me that lobster would sell for around Canadian $3 per lb. There is significant competition between lobstermen in the Maritimes and across the Eastern coast of North America, so the prices are driven down. However, here in the UK, the price for European lobster from a local fisherman is around £14 per Kg, that’s £6.35 or Canadian $10.48 per lb, nearly 4 times more expensive than Canadian lobster! It therefore makes ‘sense’ for restaurants to import their lobster from the US – as even with shipping, it still works out to be more economical for them to import American lobsters. I put sense in apostrophes here due to the fact that I don’t think it is very sensible at all – I am all for supporting local fishermen and think that the carbon footprint of importing lobster when we have perfectly good lobster off of our own doorstop is totally nonsensical… but that’s just me I guess!

Sampling aboard a commercial fishing vessel in 2011. 

And this is where our problem begins. Accidental escapees and carelessness means that American lobsters are often released into our waters. On top of this, ‘conservationists’ who think they are doing the lobsters a favour when they see them in a restaurant and buy them with the view of setting them free, don't realise the real damage they are doing to the natural H. gammarus gene pool. Now, to the untrained eye, American and European lobsters can look extremely similar, especially when they haven’t moulted for a while and are covered with slimy biofilm, tube-worms and barnacles, however there are significant differences and beady eyed fishermen in Norway have been reporting hybrid Euro-American lobsters (yes, really!). The lobsters are being collected by Dr. Ann-Lisbeth Agnalt at the Institute of Marine Research in Bergen, where they have discovered that unlike other interspecies cross-breeds, these lobsters are not sterile! 

American lobsters are host to some devastating diseases which have not yet been detected, or tested for in European lobsters. One of these diseases is Bumper Car Disease, caused by Anophryoides haemophila, a ciliate parasite and another is Epizootic Shell Disease (ESD), a form of shell disease thought to be caused by bacteria, amongst other stressors. Shell disease syndrome, or in crabs, Black Spot, is endemic to the European crustacean populations (see Vogan et al., 2008), but it is not as severe or as devastating to the shellfish industry as ESD is in the US.

An American lobster with Epizootic Shell Disease. 

After that long-winded introduction, this is where I come in! Is it possible for my beloved European lobsters to get ESD? How will the 'invasion' of these pesky Americans affect our native lobbies? We devised an exposure experiment to test if when they are damaged in the same way, sharing the same tank and water, would European lobsters display the same shell disease as American lobsters? When I say damaged, we imitated natural damage by puncturing the claws as they would when fighting, as well as abrading the shell with sandpaper to mimic the natural damage from shuffling around under rocks and in ‘caves’, where they would usually reside. On top of the European and American lobbies in Boston, we had a like for like experiment running at the same time in Swansea, with just European lobsters (from the same stock as the ones we sent to Boston), to see how the disease (if any) would develop alone.

We did all sorts of analysis, including swabbing and photographing the induced damage development weekly over the entire experiment (about 10-12 weeks), which were then extracted of DNA, and tested using PCR (polymerase chain reaction) for the bacteria thought to cause ESD, a gram positive critter called Aquimarina homari (Quinn et al., 2012), photographing the time final shells or moults under Scanning Election Microscopy (SEM) and placing the final tissues into histology (which I am still in the process of examining).

Top (A): European, and bottom (B): American
cuticle, check out that difference in thickness!

When looking at the bacteria, we noticed that most of it resided around the pore canals and setal pits (hairs) on the lobster shell. Pores are little indentations for the transport of ions and minerals such as melanin to the surface of the lobster and the hairs are for chemo and mechano-reception (tasting and feeling the water). We aren’t the first people to notice the bacteria hanging around these areas (Smolowitz et al., 2005) and this observation along with the hypothesis that bacteria may cause shell disease (Rosen, 1970; Sindermann, 1991) means that these are probably the aperture allowing the entry of pathogens – therefore the reason why the damage we induced gives entry to the disease.

The American lobsters had a different array of bacterial flora than the European counterpart, but we found A. homari in both species - I won’t give too much away, as that paper is still being reviewed. My most exciting finds were of that under the SEM – European lobsters have a thicker cuticle (shell) and less pores on their claws than American lobsters. This is pretty exciting for European lobsters for a number of reasons… namely because it may mean that they are less susceptible to disease. Hurrah!

So, that is a simplified version of my work so far and to me, like I said earlier, it is very exciting. I like to think that it’s good news for the European lobster, but our study was just a small in vitro fraction of the whole population, so plenty more work so be done. For more of the science, see my paper: Davies, C.E., et al. A comparison of the structure of American (Homarus americanus) and European (Homarus gammarus) lobster cuticle with particular reference to shell disease susceptibility. J. Invertebr. Pathol. (2014), http://dx.doi.org/10.1016/j.jip.2014.01.001, and if you can’t access it, just leave me a comment or send me an email to get a copy – if anything, the pictures are pretty awesome. It’s currently only online
but should be in print within a couple of months!

References (I tried to link them all, but not sure who will be able to access them if you're not on a subscribers network)

Jørstad, K.E., Agnalt, A., Farestveit, E., 2011. The introduced American lobster, Homarus americanus in Scandinavian waters. In: Galil, B.S., Clark, P.F., Carlton, J.T. (Eds.), In the Wrong Place – Alien Marine Crustaceans: Distribution, Biology and Impacts. Invading Nature – Springer Series in Invasion Ecology, vol. 6. pp. 625–638.

Quinn, R.A., Metzler, A., Smolowitz, R.M., Tlusty, M., Chistoserdov, A.Y., 2012. Exposures of Homarus americanus shell to three bacteria isolated from naturally occurring epizootic shell disease lesions. J. Shellfish Res. 31, 485–493.

Rosen, B. 1970. Shell disease of aquatic crustaceans In: Snieszko, S.F. (ed) A symposium on diseases of fishes and shellfishes. Special Publication No 5. American Fisheries Society, Washington, DC, pp 409–415.

Sindermann, C.J. 1991. Shell disease in marine crustaceans—a conceptual approach. J. Shellfish Res. 10, 491−494

Smolowitz, R., Chistoserdov, A.Y., Hsu, A., 2005. A description ofthe pathology of epizootic shell disease in the American lobster, Homarus americanus,H. Milne Edwards 1837. J. Shellfish Res. 24, 749–756.

Stebbing, P., Johnson, P., Delahunty, A., Clark, P.F., McCollin, T., Hale, C., Clark, S., 2012. Reports of American lobsters, Homarus americanus (H. Milne Edwards, 1837), in British waters. Bioinvasions Rec. 1, 17–23.

Vogan, C.L., Powell, A., Rowley, A.F., 2008. Shell disease in crustaceans – just chitin recycling gone wrong? Environ. Microbiol. 10, 826–835.