My first post there, an article on the potential for anthropogenic noise to interfere with the lives of fish, is up now. Please head on over there and check it out.

Paul, the ‘Psychic’ octopus who can apparently predict* World Cup football match results, has inspired a lot of silliness attracted a lot of media attention recently. But can any other marine organisms see into the future?

Sea snakes of the genus Laticauda (Fig 1.) are not entirely aquatic – not only must they regularly return to the surface to breath, but they also reproduce on land. They hunt in relatively shallow water, searching among rocks and coral for suitable prey such as crabs and small fish which they paralyse using their venom; they are in fact among the most lethally venomous of snakes, but are not normally aggressive towards humans. They can be rather inquisitive though, which can lead to some unnerving moments for SCUBA divers (it can be quite a shock to notice a venomous snake swimming happily around your legs).

Fig. 1. Banded sea krait, Laticauda colubrina (Image source: Wikimedia Commons)

Extremely rough weather can result in difficult conditions for organisms that inhabit coastal marine environments, particularly during tropical cyclones. As well as directly damaging habitats such as coral reefs, the strong winds, high waves, and storm surges could threaten mobile organisms with injury or stranding. In environments that are regularly subject to such perturbations, animals might be expected to seek shelter in rough weather, and sheltering behaviour would be most effective if it began prior to the onset of dangerously rough conditions.

While studying sea snakes in Taiwan, Liu et al. noticed that the numbers of sea snakes they observed among tidal pools and shallow waters declined sharply in the day or so prior to Typhoon Morakot in August 2009 (Fig.2); only one individual snake was spotted on the evening prior to the onset of the typhoon, compared to 20 or more per site on other dates. Once the storm had passed, numbers of snakes returned almost immediately to their pre-typhoon levels, making mass mortality of snakes during storm conditions seem an unlikely explanation for the decline.

There are a few possible explanations. For example, if conditions were worsening prior to the storm proper, this might have made it more difficult for the researchers to spot snakes in the field – which would mean that the observed decline was simply a sampling artefact. On the other hand, if the decline was real and not just due to difficulty spotting snakes, it could have been a response to increasing wave height, rather than anticipation of a coming storm. However, the exodus began before the sea state got rougher than it would on normal windy days. Indeed, analysis of existing data found no correlation between snake abundance and windspeed (which drives wave height). Rainfall, likewise, did not seem to be the trigger for the disappearance of the snakes.

  Fig. 2 (from Liu et al. 2010). Barometric pressure over sampling period, with numbers of snakes observed on sampling days (solid points) and rainfall (vertical bars). Typhoon Morakot occurred on days 38-40.

When snake abundance was plotted alongside data on barometric pressure, however, the decline in snakes seemed to correspond rather neatly to a drop in pressure recorded prior to the arrival of Typhoon Morakot (Fig. 2.). Observed numbers of snakes were significantly correlated with barometric pressure, suggesting that the drop in pressure provided an early warning of the cyclone’s approach; and this may have triggered anticipatory behaviours that allowed the snakes to survive the storm.

However, a quick and dirty analysis of the plotted data (extracted from Fig. 2. using DataThief) shows that there was no correlation between the number of snakes sighted and pressure under non-cyclone conditions (Fig. 3). This suggests that the relationship is more complex than a simple linear relationship between snake activity and atmospheric pressure; snakes may only have responded to dropping pressure once it fell below a certain threshold.

Fig. 3. Potential relationship between barometric pressure and snake sightings; plot on the left includes all data, plot on the right excludes data from just before the storm, showing no correlation in ‘normal conditions’

This is a fairly preliminary piece of observational work, and there are a few flaws in the paper. For example, there is very little detail on the field survey methods used, and the paper is missing some other information that many would consider important to include. It’s still an interesting use of what looks like opportunistic data collected during a longer term project – and definitely worth reporting on. Ideally, a manipulative experimental study would allow a better understanding of the responses of these creatures to changes in surface pressure, and at the very least more data are needed on snake abundances at lower pressures to understand the relationship between pressure and snake activity in the field (the left hand chart in Fig. 3. has only two data points at pressures lower than about 1004 hPa).

Another question, of course, is where do the snakes go? It seems unlikely that they move into deeper water to avoid the worst of the storm, because they might be vulnerable to large predators in open water, and breathing at the surface in cyclone conditions might be difficult even some way offshore. It isn’t likely that they simply hunker down on the seabed either, because they need to return to the surface regularly to breath. The study authors speculate that the snakes make use of cavernous spaces in the local volcanic rock, which would allow them to find safe places to breath while sheltered from the worst of the weather, but the danger inherent in undertaking coastal fieldwork during a cyclone means that it will be difficult to test any such hypotheses. In any case, further observational work will be required to confirm that sea snakes really do anticipate stormy conditions and seek shelter, and to see if this is a general response of sea snakes to extreme weather, or simply an adaptation displayed by a local population.

And of course, nothing described above requires snakes (or any other marine creatures) to have psychic powers.

Y.-L. Liu, H. B. Lillywhite, and M.-C. Tu1 (2010). Sea snakes anticipate tropical cyclone Marine Biology

Direct Link (doi: 10.1007/s00227-010-1501-x) 

*I do realise that the octopus isn’t actually psychic, and can’t actually predict the future – and that snakes, sea-based or otherwise, can’t either.

TGSOE, for those who are not aware, is Dawkins’ attempt to lay out in one book the current evidence for evolution. His previous books have been more focused on explaining what evolution is and how it works, and while this inevitably involved much discussion of the evidence, he admits that nowhere has he set down an explicit catalogue of the evidence that evolution is real. I agree that this is worthwhile, not just from the perspective of refuting creationism, but also as an endeavour in its own right; the science is fascinating in any case, it is always worth knowing on what evidence a scientific consensus is built, and (outside of undergraduate evolution textbooks) the evidence for evolution is not often presented succinctly in one place.

This book fulfils that role admirably. Logically structured, it takes us on a tour of the various types of evidence that show evolution in action (or the ghost of evolution past), dealing with creationist misconceptions along the way. Artificial selection, fossils, biogeographical patterns, developmental evidence, genetic and morphological parallels and divergences among species, relations between predators and prey, the ever popular ‘bad design’ of features such as the vertebrate eye (easily comprehensible under an evolutionary account) and more; all are discussed using up-to-date evidence, alongside explanations of how the evidence itself is collected and understood. Crucially we are shown how independently strong lines of evidence all come together to build a very strong case, such that: “Even if not a single fossil had ever been found, the evidence from surviving animals would still overwhelming force the conclusion that Darwin was right”.

I was glad to see that from time to time we are even given examples of how evolutionary theory might in principle be falsified (ie. shown to be false) – presumably to forestall the bizarre creationist argument that evolution is not real science because it is not falsifiable (I suspect this stems from a basic confusion between ‘is not falsifiable’ and ‘has not been falsified’). These are usually specific examples that could refute specific aspects of evolution (rather than disproving it generally), like Haldane’s well known ‘fossil rabbits in the Precambrian’. 

A couple of negatives. Firstly, there is frequent use of the phrase ‘living fossil’. Yes, it always sits between quotation marks, and I realise that it is a commonly used phrase that people may find evocative, but I have to admit that I do not care for it, and I am not alone. At one point Dawkins’ even goes as far as to suggest:

“…’living fossils’ like Lingula which, in extreme cases, have changed so little that they might almost interbreed with their remote ancestors, if only a matchmaking time-machine could procure them a date.”

Well, I suppose he’s hedging a bit with the ‘might almost’ there, but I’m confident that no, even with the assistance of a time machine, interbreeding between individuals and their remote ancestors would not be possible. As pointed out by Dawkins himself elsewhere in the book, even where there is little or no obvious morphological change in a species, its genome will continue to change, making individuals separated by vast tracts of evolutionary time genetically incompatible. Dawkins must know this, so the above comment seems a little odd.

I did also spot one outright error*. In the section on radioactive clocks, when first being introduced to the isotopes of carbon we are told that:

“There’s also carbon-13, which is too short lived to bother with…”

Dawkins is right to think that carbon-13 is of no value to radiometric dating, but that is precisely because it is not short-lived at all; carbon-13 is a stable isotope and is much more common than carbon-14, making up about 1% of the world’s carbon. 

But these are relatively trivial objections to what is an otherwise outstanding work of popular science. Having read much of Dawkins’ output, sitting down with this book was like settling down with an old friend. The writing is unambiguously clear and engaging, and the book sparkles with warm good humour and genuine enthusiasm for the subject. I personally enjoyed the book very much. Being a biology graduate, and having read a decent amount around the subject, I found that there was little in there that I had not encountered before. However, I enjoyed this refreshingly presented and updated account, not just as a renewal of my understanding of the evidence, but also as an introduction to some of the more recent examples discussed in the book. Of course, it is also a useful resource to prepare for any encounters with creationists, or even just for conversations with people who are unfamiliar with the evidence and have got the impression from somewhere that the very idea of evolution is still controversial. I would have no hesitation in recommending this book to anyone I knew who had questions about the evidence for evolution, or wanted to learn more – as it handily brings so much good information together in one easily understood package.

*[Post Script – added 23/06/10. I had a look at the paperback edition in a local bookshop today, and the offending sentence has been changed to “carbon-13, which is too rare to bother with…”. I say changed, rather than corrected, because this is not much better, especially since in both editions the sentence continues “and carbon-14 which is rare but not too rare to be useful for dating relatively young organic samples…”. This leaves the reader with the impression that it is the relative rarity of carbon-13 that makes it useless for dating, but as I pointed out, this is not the case – it is because it is a stable isotope. It does not undergo radioactive decay, so the amount of carbon-13 in a sample is not directly related to its age. Furthermore, if carbon-14 is “not too rare to be useful” but carbon-13 is “too rare to bother with”, this implies that carbon-13 is rarer than carbon-14, which is wrong. As Dawkins himself points out later in the book, “about one [carbon] atom in a trillion is carbon-14”, while I’ve told you that about 1% of all carbon on earth is carbon-13. I know this a bit of a pedantic moan about relatively trivial details, but it was a stupid mistake to start with, and ‘correcting’ it with something just as wrong seems weird.]

May’s Fish of the Month is the three-spot dascyllus, Dascyllus trimaculatus. They are very pretty little fish, especially when young, although their markings become less distinct as they get older. They’re often found in groups around small coral heads, occurring from the Red Sea to the Indo-Pacific.

Image source: www.copyright-free-pictures.org.uk

Read More and find other images on Wikipedia and Fishbase

It is time to for this tradition to be resurrected (I’m writing this on Easter Day, after all) in the new, glorious form of a regular blog post series. So without further ado, allow me to introduce the Fish of the Month for April 2010…..

Brosme brosme: The torsk, also referred to as tusk, cusk.

Image: Brosme brosme at rest on the seabed, next to the leg of a North Sea oil platform at ~140m depth. Also present is a common starfish (Asterias rubens). Image Source: SERPENT Project

You may recognise this image from the avatar I use here on the blog and on twitter. A member of the Lotidae (a group of fishes closely related to the gadoids or cod-fishes), they are a relatively common species in the western and eastern North Atlantic, and are quite easily distinguished from other cod-like fishes by their single continuous dorsal fin.

I have a bit of a fondness for this species, as I have spent many hours watching footage collected during structural inspections of offshore platforms in the North Sea, and these fish are ubiquitous around the deeper and more northerly platforms. Their typical habitat is rocky seabed and deep reefs, but they seem to be equally at home around oil rigs, often to be seen cruising leisurely along horizontal members (no sniggering), or up and down the legs. They seem to be unperturbed by the presence of ROVs (Remotely Operated Vehicles), and even sometimes appear to be a little curious.

Apparently they also taste good, but I’ve never tried them myself.

Read more:

Wikipedia

Fishbase

Hopefully, these should appear on a weekly basis (!) and initially I’ll try and post each edition on Sunday.

From the journals:

Male chimpanzees form enduring social bonds

A ten year study of a large group of chimpanzees in Kibale National Park, Uganda, has found that male chimpanzees form enduring social relationships which are not consistent with some recent suggestions that primates in general only form short-term bonds to serve their immediate needs. Some pairs of males showed strong social bonds, spending above average amounts of time together over periods of several years, and such pairs often showed a greater degree of equality in their grooming behaviour. These interactions were affected by kinship; males who shared a genetic mother formed longer lasting and more equitable bonds. However, unrelated males still formed strong bonds, with individual males typically having at least one long-lived association, some of which lasted the entire length of the study period.

J. C. Mitani, Male chimpanzees form enduring and equitable social bonds, Animal Behaviour (2009), DOI: 10.1016/j.anbehav.2008.11.021

Harvesting for human usage drives rapid phenotypic change in wild populations

Many species are heavily harvested by humans for food or other purposes. This pressure results in a variety of negative effects, among which are changes in morphological traits (such as size), and life history traits (such as age/size at first reproduction). On average individuals in a population become smaller and breed earlier as the larger and later reproducing individuals are consistently removed from the environment in large numbers. Since larger, later maturing individuals often have greater reproductive success over their lifetimes, this exacerbates ongoing declines in population size. An analysis of data on these trait changes in several exploited populations has compared them with those occurring in populations affected by natural perturbations (such as Galapagos finches hit by droughts) and found that changes driven by human exploitation are greater in extent, and – critically – occurring over much shorter timescales.

C. T. Darimont, S. M. Carlson, M. T. Kinnison, P. C. Paquet, T. E. Reimchen and C. C. Wilmers, Human predators outpace other agents of trait change in the wild, Proceedings of the National Academy of Sciences (2009), doi: 10.1073/pnas.0809235106

Camouflage requires corresponding behaviour in order to be truly effective

While it might seem a trivial observation that camouflage is only really effective when you keep still, there is little rigorous data on the association between crypsis and behaviour – and how the interaction between these two factors affects the risk of predation. Experiments involving three-spined sticklebacks (Gasterosteus aculeatus) feeding on insect larvae, verified that the effectiveness of cryptic colouration was dependent upon how much the prey moved around. Motionless and cryptic prey were seldom eaten – while moving about rendered their camouflage ineffective (in comparison motion had little, if any, effect on how likely non-camouflaged prey were to be eaten). Cryptic colouration is a common anti-predator defence – but is only really effective in conjunction with suitable behaviour, indicating that such behaviour must co-evolve with the morphological adaptations.

C. C. Ioannou and J. Krause, Interactions between background matching and motion during visual detection can explain why cryptic animals keep still, Biology Letters (2009), doi: 10.1098/rsbl.2008.0758

From the blogosphere:

Hold the front page: Tree of life not an actual tree

New Scientist provoked the ire of several science bloggers this week, with the front page declaring “Darwin was wrong”. This was accompanied by an article explaining why the ‘Tree of Life’ analogy is flawed in several respects. Who knew? PZ Myers of Pharyngula was not impressed, Larry Moran at the Sandwalk blog went into a bit more detail about his problems with the headline, and Jason Rosenhouse of EvolutionBlog was fairly scathing in his assessment of the content of the article – “the article has only the yawn-worthy old-news that horizontal gene transfer among single-celled organisms means that the metaphor of a tree of life must be modified”.

Don’t you just love the delicious taste of cuttlefish? Mmmm. Don’t know about you, but for me that nasty ink really ruins the soft, tasty flesh – and let’s not even get started on the bone. Yuck!

Well folks, today I’m going to show you a quick an easy way of preparing a cuttlefish, for a fast and nutritious snack. And you won’t need any cooking equipment…. or even any functional arms. All you need is a sturdy snout.

First you’re going to need to get hold of a nice juicy cuttle. I recommend the Spencer Gulf, off South Australia, where they come together in huge numbers for a bit of you-know-what, every year from May to August. You should have no trouble seeking out a slightly *ahem* worn out individual. First you need to get them out onto open sand – I’m sure you can all manage that part! Next you need to dispatch your lunch as quickly as possible. Position yourself above the cuttle, pointing your body vertically down. Now, there’s a bit of a knack to this next part, so you might need to practice, but what you need to do is drive yourself down, hard, using a tail beat, and add a bit of a twist. This kills them instantly.

Now your meal isn’t trying to get away, you need to prepare it. Presentation is everything! First: that ink. Lift the cuttle up into the water column and then beat it with your snout – this forces the ink out. Repeat until there’s not so much ink coming out, and now you’re ready to deal with the bone.

Bring your cleaned cephalopod back down to the sea bed and place it on its back. Push it along the sand….and…hey presto! Rubbing it on the seabed strips the skin off the back and that annoying bone just pops out.

After that you’re left with a wholesome and tasty snack. Prepared in next to no time!

Below is our special cut-out-and-keep quick reference card, so you don’t forget how to prep your cuttle.

Happy Hunting!

6 easy steps to a tasty snack!

Julian Finn, Tom Tregenza, Mark Norman (2009). Preparing the Perfect Cuttlefish Meal: Complex Prey Handling by Dolphins PLoS ONE, 4 (1) DOI: 10.1371/journal.pone.0004217

The paper (Hoegh-Guldberg et al. 2008) is a discussion of something the authors term “Assisted Colonisation”; a proposed conservation methodology which they suggest might well be applicable for the amelioration of some of the ecological impacts of climate change.

Most species can only persist within a relatively narrow range of physical conditions, often constrained within a certain geographical area. As physical conditions (for example, temperature) shift as a result of climate change, this area can shrink, or move (generally moving towards the poles). While some species may be able to physically move themselves to stay within their optimum conditions, others cannot (this might lead to ecosystems being ‘torn apart’ as different species in an ecosystem will be able to move at different rates). In any case, organisms will only survive if they are able to expand/shift their range into areas of otherwise suitable habitat. Furthermore, as the species move, they may meet areas of unsuitable habitat, at which point their range will begin to shrink.

The authors of the paper start by making the case that conventional conservation practices may not be sufficient to preserve species that are susceptible to this problem, and they offer up for consideration the possibility of ‘assisted colonisation’: in other words physically relocating species to suitable habitat which will be at a suitable temperature for them to survive. They recognise that deliberate species relocations have a long and dismal history, but maintain that it may be possible to identify species for which it is a suitable option. They propose a framework for assessing the suitability of this controversial idea, which I have included below.

It all seems very feasible and pragmatic, put like that.

However, there are some problems beyond the obvious ones concerning introducing species into habitat where they were not originally present. I’m going to focus on the marine examples the authors cite, because they’re right in my area. But first, it is worth mentioning what looks like an obvious flaw in their thinking. Theirs is very much a single species-oriented approach….. which seems to me to be a problem. Species do not exist in an ecological vacuum. Unless you’re very lucky, and find habitat elsewhere that is perfectly suitable but lacks the target species (which might occur in situations where a species range has fragmented and other areas of suitable habitat exist), then that’s all very well. But it seems likely that populations transposed in isolation might not fare well. By extracting them from their natural range you’re causing the very problem that we want to avoid: tearing apart an ecosystem. Really, you’d need to transplant a whole slice of ecosystem, somehow preserving all the linkages between species. Excuse me if I find that impractical.

They also make a suggestion about using artificial reefs to facilitate the shift in range of rocky reef species (which would otherwise be blocked by the lack of suitable hard substrate): “It might be practical, at small scales, to establish artificial, three-dimensional reef structures ahead of migrating coral, fish, and invertebrate species”. Well, “small scales” is exactly right! The logistical requirements of provision of sufficient artificial hard habitat for this to be effective boggle the mind. The best hope would be to use decommissioned oil platforms (I’ll be getting to that in later posts!) to provide new habitat, but even that (a huge endeavour) is likely to make a hopelessly small contribution to the requirement for new habitat. And of course the other problem, paradoxically, is that it might work too well! It is becoming recognised that artificial structures (such as seawalls) can act as invasion corridors for alien species (Bulleri and Airoldi 2005), so by providing a handy way for invasive species to expand their range we might be making things worse in other habitats!

Another possible technique the authors mention is transplanting widespread species ‘within their range’. The idea behind this is that where you have locally adapted populations, you could transplant individuals from lower latitudes (with better heat tolerance) to higher latitudes, where the existing populations are threatened by rising temperatures. Well, for starters you’ve got to be sure that the differences between the heat tolerances of the two populations are inherited, and not due to phenotypic plasticity (where individuals with no genetic difference for a particular characteristic develop differently when they grow in different conditions). The example they use is a curious one: Acropora corals. However, the paper they cite in support (Berkelmans and van Oppen 2006) shows that the variation in heat tolerance is not due to genetic differences between populations, but due to differences in the composition of the zoozanthellae within their tissues. Perhaps this is a minor quibble, as the differences may still technically be inherited, but I can’t help but feel it illustrates the point I made above: we need to be really sure that the differences are genuinely heritable, or your costly and complex transplant endeavour is going to be a complete waste of time.

These are some of the reasons that I am wary of this approach. In order for it to be successful, and to avoid any unwanted negative effects, we would need an extremely detailed understanding of the ecology of the species involved, so that we can with relative certainty predict how they will respond to transplant, and how other species might be effected. I suspect that there are few, if any, species or ecosystems for which we have that level of understanding.

Nevertheless, the authors do acknowledge some of these problems, and we can’t necessarily afford to dismiss this approach out of hand. Climate change will prevent numerous challenges to ecosystems, and we need as many different tools as possible to ameliorate any impacts we are unable (or unwilling) to prevent. In any case, any attempt at ‘assisted colonisation’ will have to be very carefully considered: will the possibility of saving a crucial species ever prove worth the risk of making things worse in existing habitats?

Refs:

Hoegh-Guldberg, O., Hughes, L., McIntyre, S., Lindenmayer, D. B., Parmesan, C., Possingham, H. P. & Thomas, C. D. 2008. ECOLOGY: Assisted Colonization and Rapid Climate Change. Science, 321, 345-346. DOI:
10.1126/science.1157897

Bulleri, F. & Airoldi, L. 2005. Artificial marine structures facilitate the spread of a non-indigenous green alga, Codium fragile ssp tomentosoides, in the north Adriatic Sea. Journal of Applied Ecology, 42, 1063-1072. DOI: 10.1111/j.1365-2664.2005.01096.x

Berkelmans, R. & van Oppen, M. J. H. 2006. The role of zooxanthellae in the thermal tolerance of corals: a ‘nugget of hope’ for coral reefs in an era of climate change. Proceedings of the Royal Society B: Biological Sciences, 273, 2305-2312. DOI: 10.1098/rspb.2006.3567

]]> http://artificialhabitat.wordpress.com/2008/07/18/assisted-colonisation/feed/ 2 artificialhabitat http://artificialhabitat.wordpress.com/2008/04/21/a-novel-disease-of-the-shore-crab/ http://artificialhabitat.wordpress.com/2008/04/21/a-novel-disease-of-the-shore-crab/#comments Mon, 21 Apr 2008 11:54:41 +0000 artificialhabitat http://artificialhabitat.wordpress.com/?p=95 ]]> For F. Happy Birthday!

Aquaculture is often seen as an important way to address the growing food needs of human populations, without the environmental costs of harvesting from wild populations (such as habitat destruction and overfishing). Unfortunately, ‘farming’ of marine species for food often has significant environmental impacts of it’s own, for example the destruction of large swaths of mangroves for the construction of shrimp farming ponds, and the organic enrichment of marine habitats by wastes from fish farms.

Aquaculture has other problems to contend with, aside from the potential environmental effects. Rearing of large numbers of individuals of a single species, in close quarters, inevitably raises the risk of disease – which can lead to significant economic costs: lost production, administration of antibiotics, treatment of infected animals, etc.

One species which is under consideration for aquaculture is the European shore crab, Carcinus maenas, which is used as bait by anglers and (apparently) as a food in continental Europe (those crazy continentals….. I can’t say that I find myself tempted to eat this particular species). However, there seem to be some problems with culturing this particular species – one of which is a previously unknown disease which is seen to infect a significant proportion of crabs under aquaculture conditions (present in less than 1% of wild individuals). Scientists at Swansea University (Eddy et al., 2007) investigated this previously undescribed disease, which they call ‘milky disease’ due to the fact that the haemolymph (crab blood, to the uninitiated) of infected crabs takes on a milky appearance, and to find out what the disease agent is, what effect it has on infected crabs, and how it is transmitted.

What effects does the disease have? Crabs with milky disease show no-external symptoms, the only obvious sign being the milky appearance of the haemolymph. Infected crabs have higher levels of ammonia and glucose in the blood, but reduced numbers of circulating blood cells and protein. Certain cells of the hepatopancreas and gills of infected crabs appear to be physically affected by the disease, but other tissues appear normal. Nonetheless, the infection is lethal; usually within seven days of when the crabs are first observed to have milky blood.

What’s causing the disease? Haemolymph samples from infected crabs appear to contain large numbers of tiny, bacteria-like particles which are not present in healthy crabs. Detailed electron microscopy work also shows the presence of these bacteria in hepatopancreas cells, as well as bacteria apparently escaping from ruptured cells.

The causative agent turns out to be, as suspected, a bacterium. While it obstinately refused to be cultured, DNA techniques show that the organism responsible for milky disease is a previously unknown member of the alpha-proteobacteria.

In situ hybridisation is a molecular technique which is used to identify the physical presence of a specific DNA sequence. It works by using short DNA sequences (called ‘primers’) which will only attach to the DNA sequence that you’re looking for. These primers are labelled with chemical compounds which allow (after further processing) you to actually see where the DNA is. In this case, a sequence unique to the milky disease bacteria was used, so that once developed, slides of crab tissues could be inspected to see exactly where in the organism’s body the bacteria were most concentrated. This technique confirmed the presence of the bacteria in the hepatopancreas, and also in some blood vessels and connective tissue, while showing that it was, indeed, absent from most other cells and tissues.

The researchers were not able to induce infections in healthy individuals, so the route of infection is, as yet, unknown. Crabs injected with haemolymph from infected animals do die within 24 hours (even if the injection is free from bacterial cells), despite the absence of typical milky disease symptoms. This suggests there might be some toxic effect killing the crabs, perhaps due to bacterial waste products. However, direct injection of infected haemolymph is not a natural situation, and crabs fed infected food did not show any sign of infection, so further work will be needed reveal the natural route of infection.

So, while there are obviously still questions, this study goes some way to helping us understand this ‘new’ disease, and it’s effect on one particular species. Presumably, work will continue.

While the disease is rare in the wild (less than 1% of crabs infected), under aquaculture conditions the disease is much more prevalent (up to about 25% of crabs infected) – though only during the warmer months. This has several implications. Firstly, it shows that even diseases which are not a serious problem for wild organisms are still a potential threat to aquaculture. Perhaps aquaculture operations could thus also act as reservoirs for disease agents, which could then spread into wild populations. Design of aquaculture operations should attempt to take this into account, for example by treating effluent and preventing escapes.

The fact that infection rates are highest in warmer months is also of concern. It means that climate change may have negative impacts on all aquaculture operations where water temperatures are rising, but also that in general rising water temperatures could lead to higher disease incidences even in wild populations.

Eddy, F., Powell, A., Gregory, S., Nunan, L.M., Lightner, D.V., Dyson, P.J., Rowley, A.F., Shields, R.J. (2007). A novel bacterial disease of the European shore crab, Carcinus maenas molecular pathology and epidemiology. Microbiology, 153(9), 2839-2849. DOI: 10.1099/mic.0.2007/008391-0