Zombie Crabs – Why Can’t We Get Us Some of Those?

I originally wrote this article for the Washington Sea Grant Crab Team newsletter, and you can read this and much more crazy things about marine life on the Crab Team webpage.

The yellow blob under the abdominal flap is not eggs, but the
extern of a female barnacle, Sacculina carcini. (By Auguste
Le Roux (Own work), via Wikimedia Commons).

In Europe, millions of zombie green crabs are roaming the shore. From the outside, you might not even realize they are brain dead, no longer truly a green crab, but have been transformed into a skittering, feasting, parasite-producing machine. Their metabolism has been co-opted, their reproductive system re-appropriated, their crabby will subjugated to the whims of the intruder they harbor – the parasitic barnacle Sacculina carcini.

Barnacle? That’s right. For these crabs infection is the stuff of horror films, but the monster in this case is not an animal we typically think of as gross or dangerous – though anyone who has tried to walk barefoot on a barnacle-encrusted rock might disagree. This species is one of a group of parasites called Rhizocephalans (meaning “root headed,” which will become clear later on). As free-swimming larvae, they look very much like other barnacles, progressing from a nauplius stage to a cypris – but here they diverge.

The great biological illustrator Ernst Haeckel visualized
what the root-like intern of Sacculina carcini would
look like inside the crab. And the blob of the extern
is exposed by the folded back abdomen (Wikipedia).

Imagine this: you are a European green crab, minding your own business, maybe poking around looking for some tasty polychaete worms or clams to eat, and you feel a slight tickle when something microscopic lands at the base of a hair on one of your legs, clinging to you by means of an antenna-like appendage. But you’re too distracted cruising around the shore to notice when the larvae — which has shed its shell, legs, eyes, and brain as it metamorphosed into a kentrogon (sounds like some kind of alien race, but is basically a sac of cells with a needle where the head used to be) — injects itself into your body through the base of that hair, and is released. Soon, the parasite attaches to your digestive system, and begins to grow thread-like structures that wrap around and along your nerves, like ivy growing up a tree – called the interna. The interna ultimately spread throughout your entire body, like the roots of a tree filling up a pot.

You might start to notice something going on when you begin to look like a female crab – that is, if you weren’t already female. One of the most bizarre effects of being infected with this barnacle is that, even though both sexes can be infected, male crabs are feminized by the parasite, causing them to have smaller claws and wider abdomens, like females (read a study on host feminization), paving the way for what happens next.

Gah! The life cycle of Sacculina carcini, from Goddard et al. 2005.

The barnacles that infect crabs are always female, and they use the crab as an egg factory, feeding off the crab and ultimately growing out through the underside of the crab to create a blobby structure called an externa, which is a large sac of barnacle reproductive tissue. The crab carries the externa just as if it were his or her own eggs. The barnacle eggs in the externa are fertilized by one or two free-swimming male cyprids, and then released as the next generation of zombifying parasites.

Needless to say, when you are carrying a sack of parasites on your abdomen, there’s no room for eggs of your own. Infected green crabs, both male and female, are fully castrated by the parasite. In addition, infection ultimately halts the process of molting, so crabs not only can’t grow any larger, but they also can’t replace any lost limbs. In spite of its gruesomeness, infection is not a death sentence for European green crabs; about half of the crabs infected in a laboratory experiment survived infection for at least 3 months. In the native range, some crabs also show scars on their carapace from carrying previous externae. However, those crabs can never recover their reproductive ability, and the female parasite can create multiple externae for the remaining life span of the crab.

How does this fit in with the global invasion of green crabs? In the native range of Carcinus maenas, about 16 percent of crabs are infected with Sacculina carcini (read the study), and given that about half of infected crabs die, this parasite could be a substantial part of population regulation. However, S. carcini has not followed European green crab to either the east or west coast of North America. It’s likely that the crabs that first traveled across the Atlantic Ocean, and later across the United States, were too young to bring the barnacle along as a hitchhiker. Additionally, because the male barnacle that fertilizes the female’s externa is free-swimming, the male and female barnacles need to make it to the new range at just the right times, but in different ways, which could be a very unlikely coincidence.

The lack of this, and other parasites, is one possible explanation for why European green crabs are larger here on the West Coast than they are in their native range (read the study). Combine a lack of parasites with relatively cold water (read the study), and it turns out that the biggest green crabs in the world have been found in the Pacific Northwest. Some claim to fame!

Your mind might already be leaping to the next logical question: Can we bring this parasite to help control populations of the European green crab on the West Coast? In the Salish Sea we do have native species of Rhizocephalan parasites, even some in the same group as this one. Nevertheless, it turns out bringing Sacculina carcini over is probably not a good idea. For those of you familiar with the history of cane toads in Australia, you’ll be relieved to hear that researchers here have been doing their homework when it comes to this parasite.

In a laboratory experiment in Santa Barbara, scientists tested whether several species of native crab could also be infected by Sacculina carcini. While more of the parasites settled on European green crab, when given the choice, they also settled on Dungeness crab and two species of shore crab that are found in our area (Hemigrapsus nudus and H. oregonensis). Dungeness crab were more likely to become infected with the parasite than any of the other species of crab, even when relatively few barnacles settled on them. What’s more, all of the native crabs that became infected died, compared to only about half of the European green crabs that were used for comparison, and many of the native crabs showed neurological impairment as a result of infection. A number of questions remain about whether the same patterns would occur in the field, but for now, the risk to native crabs is significant enough to warrant caution.

Friday Fluff #4: For when enough is enough

Enough is officially z'nuff and I pronounce this week over. It's been a long and pretty sad week as, amidst the national pain following the shooting in Orlando, the field of ecology lost a literally towering figure with the passing of Bob Paine. There's been a lot of opportunity to reflect on his contributions to the field, and I've spent time reading some of his interviews (including one I participated in) as well as pieces others have written about him. I think the best thing to do is to take some time to marvel at the ridiculously elegant nonsense that nature has come up with, and then get back to work.

With that in mind, here is some ridiculously elegant nonsense that is perfect.

Thing the first:

When mollusks collide, arthropods win.

View post on imgur.com

Thing the second:

I meant to post this months ago when David Bowie died. I think the unintentional wait was worth it, because the content has kept growing. I have a soft spot for the sailor version of Onchodoris muricata...

http://bowiebranchia.tumblr.com/

Thing the third:

I also loved this recent video from Emily Graslie at the Field Museum. She meets with the Invert Collections Manager, Jochen Gerber, who pulls some of the coolest snails out to talk about with her. I know they are the coolest because they are my favorites too, including the Snail of Ice and Fire, Aviator Snails, and Conchologist's Conch. I also got some inspiration for a future Species species of the Week week...but more on that later.

PS!
I'm now on Twitter, because I heard it was a dying medium - so I think that makes me hipster? Follow @rahrahradula

Game of Shells OR A Song of Calcium and Mucus

Who's pumped for the premiere of the first season of Game of Thrones to surpass the plot as written in the book series?! I'm pumped! Even the mollusks are pumped! Jumping on the bandwagon left and right, so why don't I join them.

Get ready for Game of Shells...cue intro music(2).

A Parade of Champions! Chrysomallon squamiferum

Father of Sand Snakes Snail, Kingslayer Snail, and Emo Snail: By Chong Chen - Own work, CC BY-SA 3.0.

You could be forgiven for mistaking this trio of well-protected knights as the Lords of Westeros, but in fact these are just three deep sea snails (Chrysomallon squamiferum) who are seriously into cosplay. We have, of course, (top left) The Red Viper of Dorne, Oberyn Martel, (top, right) Kingslayer Jaime Lannister in his Kingsguard gold armor and white cloak, and, naturally, front, center, and brooding as ever, Jon Snow in his Night's Watch blacks.

These guys are into extremely realistic armor reconstruction, and that chain mail is actually made of iron (except the white one, it turns out), even if does look a bit like shag carpeting. The so-called Iron Snail is a denizen of deep water hydrothermal vents(3), particularly those known as black smokers which are spewing water so hot (>350C or 660 degrees Farenheit) that it has dissolved iron sulfide in it.

That's right, these snails live in what is basically a volcano and use the lava to make their own armor. Cosplay or not, these snails are freaking terrifying/awesome/amazing/terrifying(4). And I haven't even gotten to the part where they enslave bacteria to live in their guts and make their food for them!

Appearance and present metaphors notwithstanding, we don't yet know what these iron scales are really for. Defense seems an obvious possibility(5), one that is perhaps supported by the fact that their operculum (the door the snail closes when it hides in its shell) has become so small as to actually be embarrassing. You could imagine these guys retracting into their shell when faced with, say, a terrible-claw lobster (it's an ACTUAL THING), and facing their enemy with hundreds of plates of Nope. 

Another theory is that they make the scales and fill them with iron because they have to to keep from getting poisoned by all the iron, i.e. detox. The shell is also covered with iron-rich compounds like pyrite (fools cold) and greigite - the latter of which makes the snail, you guessed it, magnetic. That could be a serious/hilarious liability on the battlefield(6).

Nevertheless, I bet Sansa Stark wishes she had Chrysomallon squamiferum as a champion instead of useless Ser Loras(7), I know I do. You can read more about this snail from people who actually know something about it here.

Eyes in the back of his...back!

Ready for battle, or to just sit there and avoid it by pretending it's not happening, is that chiton poop I see? Clearly we've scared the pseudofeces out of him. Sorry guy.

I can't quite put my finger on the right Game of Thrones reference for this one. Maybe Bran's three eyed raven pal? Regardless, clearly this guy is ready for battle because he can see a threat coming from any direction. Chitons, which I really don't spend enough time on on this blog, are like slugs with interlocking plates on their back. They look a lot like pill bugs you find under rocks, or maybe armadillos, but they are not even close to either. The main way they stay alive is to, quite literally, keep a low profile, and be really hard to get off the rock (8). 

But it takes energy to suction your body to a rock, and it means that you can't move to the next patch of artisinal and highly nutritious rock goop, so they can't do it all the time. But how do they tell they are in danger and need to batten down the hatches when their face is stuck to a rock? They cover their armor with hundreds of tiny eyes! Tiny eyes that are made of minerals! Which actually scientists have known about for a long time, but only just figured out how they work! Here's a video (they need some better background music, might I suggest (2)), and another piece about it, mo science here. Totally sweet and and completely paranoid security system. 

So who will be the next favorite to get Ned-Starked? Whatever, there's no way of knowing, and honestly, so much of the speculation around who dies next is basically meaningless, because you don't know(9). NONE of you knows. I think we can be confident it won't be any of our mollusk champions though. If only because they aren't actually on the show - which is perhaps the only way to be safe from George R.R. Martin's cruel cruel imagination.


References and Miscellany

(1) What happened to number 1? It became 9 and I didn't feel like renumbering. Deal
(2) Please keep that on repeat as you read this post. You're welcome.
(3) You know the places that spawn only things that you see on some documentary about what a freak show Nature is, and then they definitely return to haunt your nightmares pretending to be your Committee grilling you at your defense? Oh wait, or is that just me?
(4) butreallytheyareterrifying
(5) These guys like that theory too.  
(6) Why is that not a Wile E Coyote bit?!
(7) I can probably just look this up on ASOIAF wiki, but what is the deal with "Ser". Why is everything in these books just spelled to confuse, is it really a necessary part of the world building? Cripes.
(8) Wow there's a lot of these this time: This one was just to point out that there is a reason I do my research on snails, you just try collecting thousands of chitons one at a time).
(9) But I can recommend this well-reasoned approach.

Grinnin' and pickin' OR From the Annals of Never Again Cited Research

Exhibit A. The author, birthday princess, destroys crustaceans as celebration ritual. Date? Let's just say: pre-Y2K.
At right, the one remaining shot glass I can find. There was definitely an "I got crabs in Maryland" one at some point.

A lot of people, especially in the PNW, love crabs because they are tasty, but, and here is a confession that I hope nobody ever finds out: I don't eat crabs [anymore]. I grew up in Maryland and every year for my birthday we'd pick blue crabs. I remain fiercely proud of that part of my heritage, as evidenced my collection of unused shot glasses. But by college I had phased all meat, including seafood, out of my diet. My crab-picking skills, earned at the cost of a thousand million cuts to that sensitive part of my fingers between the nail and last knuckle, seasoned with Old Bay and left sizzling for days(1), are moot, a party trick at best.

I love crabs because they are fierce, because they have personality, and they have a rep for holding it down in the intertidal. I enjoy feeding crabs by hand because I'm a total weirdo, and I find it completely satisfying. Here, you watch this and tell me if I'm crazy.

Super intense, right!?(2)

There are numerous examples in the literature of crabs keeping snails at bay by just straight up eating them. Thus, you might surmise, if you have read way back in this blog to the part where I used to write about actual science that I actually did, that I would be reeeeeeeally curious to see if crabs would eat any of my invasive snails - in particular my favorite Mollusca Non-Grata, the Japanese oyster drill (Ocenebra inornata(3)). Previous research, done by,  *cough cough*, yours truly, pointed to at least a willingness of crabs to eat these snails when you throw them in a bucket together. But that's frankly pretty unimpressive - crabs will eat anything you throw them in a bucket with. What happens in natura(4)?

It was just like this...Photo of the author in her natural habitat
Credit: Nima Yazdani.

Answering that question was the goal of my summer of 2011. And if you're wondering, gee, Emily, that was HALF OF A DECADE AGO, why are you telling us about this now? It turns out half a decade is exactly how long it took me to get this work published(5)!

I'll set the scene: Emily, way out on a beautifully restored native oyster bed on only the sunniest of sunny PNW days, clean and well rested, scratching her chin and waxing genius about ecological dynamics of restoration.

J slash K. It was nothing like that. I had so much generous help. Second off, it never looked like I had it together out there even for a second. Field work is a slog. When you do work in the intertidal, it's a panicked slog, as you race to get your work done before the tide comes back. In the muddy intertidal, it's a panicked slog in painful, hilariously clumsy, slow motion as you race against the returning tide ankle deep in mud. I consider myself relatively fleet of foot in moving across mud in waders, but it's not pretty, I assure you.

So I called for help. I had a slew of helpers: 

• Nima, a classmate's husband, who was interested in seeing what the work of scientists actually looks like. He took the beautiful picture above.  I'm grateful not to have seen any close ups of what I actually looked like that day. 
• Avanthi, a classmate's girlfriend (now wife :) ), who was an amazing trooper, helping me swap out oysters on very little sleep as I recall. 
• Marie, my actual classmate, she and I carried approximately 17 million tons of rebar down the shore and across the mud - how we did it, I can't remember. I think it was one of those, well, there's really no one else who's going to do it if we don't - moments.

I also had excellent logistical support from a number of people:

• Brian Allen at Puget Sound Restoration Fund helped me get access to the oyster beds, which were under PSRFs restoration care - they put out old oyster shell to provide habitat for new babies to settle on. Brian also tried his best to teach me to pilot a tiny Whaler with an outboard, and I discovered that there are some skills that I need more than 2.5 minutes to learn. To this day, I cannot operate an outboard.
• Joth who gave me sacrificial oysters from his own farm! That's right, the shirt off his back to support graduate research. 
• Molly and her father Greg, who helped ferry me said oysters.
• Jen, my advisor, who taught me how to make oyster pops, and helped me secure lots of random supplies for building cages. "Sure, you need 20 old oyster bags? I'll have Alan bring them up and leave them outside Kincaid". 
• Not LEAST, Dave and Sue, the amazing couple who not only helped me get beach access from shore (note previous comment about inability to learn how to pilot a boat), but invited me in for coffee (pre tide flat) and soda (post tide flat) multiple times. Seriously, I can't tell you how much I love meeting the lovely shoreline owners!

This list doesn't even include my co-author Eric, who stuck it out with me through a long writing, rewriting, analyzing, re-analyzing, revising, and, yes, re-revising, which was evidently so traumatic that it caused his lung call it quits and spontaneously collapse. Sorry, Eric.

So that picture where I'm out there looking like John Muir on my own doing science and looking ruggedly picturesque - that's not what it's like. This is a list of 11 people who made this one tiny(6) experiment possible, and that doesn't include the grad students who reached deep into their closets and donated as many wire hangers as they could muster (which, naturally, I didn't end up needing...), and Alan who drove the oyster bags up from Willapa, and Eddie who tolerated the mess I made on the loading dock, and the guy who stole all the rebar from the loading dock - wait that last one maybe doesn't need a thank you.

But you get the point. It takes a village people, this is how the sausage is made, and now the paper is published (Link here click on me, I am a link and I will take you to Emily and Eric's paper, and you clicking on me will increase the paper stats! Even if you don't think that sort of thing should be important, it is. So click on me, come on, why haven't you clicked yet? Seriously, you read this far and haven't clicked? For Shame! <--Did you find the Easter egg in there? is it an Easter egg if I tell you it's in there?). 

In classic Emily style, I managed to get my act together to write this post only too late to give you access to the paper via the temporary open access link. Now it is paywalled (but you can email me). So I'll have to write another post where I tell you what all the fuss was even for, but first, I have to remember.

TUNE IN NEXT TIME TO FIND OUT

(Fair warning: there's a good chance you will be disappointed).


References and Miscellany
1. Seriously, I love Old Bay, but the trauma of picking remains in my flesh memory. 
2. Confession number two of this post: mostly I just put that music on there to cover up my voice in the video. I thought this added an air of drama to the proceedings. The crabs I trained to eat from my forceps were really chill, they knew they didn't need to go crazy to get their din din.
3. For more history on previous work with this species, check out OG Blog stuffs here and here.
4. How completely obnoxious is it to say it in Latin instead of just swapping the last "a" for an "e"?!
5. Even after I quadrupled the number of monkeys working at typewriters and it STILL took that long!
6. Really, I can't even tell you how small this in the scheme of things, and yet what an unbelievable amount of work it was.

Snails on my face?! WHERE DO I SIGN UP?!

My brother sent me this picture last night, and at first I chuckled because I thought it was a typo.

Should be "nail repair cream" Hahahaha. Snail repair cream! That would be pretty funny, can you imagine?! Think of all the crushed snails I could put back together with this amazing product! Hahahaha. And then I stopped laughing because the word "snail" was repeated in the byline. Oh they're not joking, I'm really supposed to repair snails with this?

Nope, the snails repair me! Oooooh!

First ingredient is "Snail secretion filtrate" (1). Hmm... Don't get me wrong, it should, perhaps be clear from this blog that I'm 100% fine with snail slime(2). But who says that "secretion" is slime anyway? The USDA should really get a better grip on that. I can think of lots of other things that snails secrete that I have no interest in having on my face. But OK, for the sake of argument, let's take them at their implication that it is slime, or snail mucin, which is a little more precise.

At this point, most of you are probably bored by my completely predictable failure to pay attention to anything that's going on in the world, and this snails-on-your-face thing has been all the buzz for a while. To which my response is an exasperated, tired, Duh. I'm always 3 years late on everything(3) and, thankfully for you, my point here is not "Whaaa? People are crazy!" Because that is 100% obvious and goes without saying. I mean really, it's insulting how little you think of me.

Meta-self-critique aside, I get that people put snails on their faces and it's the best thing they ever did for themselves. And you know what, that's fine. Whatever, you do you, and feel good about it, and that's great.

But the burning question, here, is how do you get the snail mucus in the jar?

Thank God there is a sub-Reddit on that very subject. These contributors were very interested in snail welfare, which is more than most, so good on 'em. Helpfully, there are two videos (in French(4)). Studying marine snails, I haven't really paid much mind to snail farming, Heliculture for us jargon snobs, which is, of course, a thing because escargots. Culinary snails are mostly terrestrial, literally the kind you find in your garden(5). Basically, snail farms do look like my garden - glad I'm doing something right there - complete with little snail shelters, which are boards you flip over and, predictably, are covered with a ton of honkin' snails.

In both of the slime-iculture videos, snail slime is acquired by agitating the snails, poking or shaking them to get them to produce slime. In Chile, a small collective of women gather the slime by hand, first rinsing colanders of snails, then holding them up one at a time while gently prodding them with a stick and allowing the slime to drip into a jar (that jar full of snail goo was admittedly a little difficult to look at). In France, the operation is more mechanized: against a stainless steel backdrop, several hundred snails are suspended in netted mesh bags and gently shaken, either mechanically or by hand, over a tub that collects the elicited slime.

Happy Snail?

One Redditor comments that the shaking method looks "less nice" than the gentle stroking the Chilean women give the snails. I suspect that reaction has more to do with the stainless steel than the snail's actual experience. Because, let's not kid ourselves here, in either case, to the snail, these processes are the equivalent of a hungry bird, repeatedly poking at the snail hiding in its shell, or tossing it around to crack the shell. This is a stress response. A snail does not expend that much energy producing so much mucus because it is "relaxed"(6). 

Why would it produce slime in response to a threat? My first thought was that the mucus could be distasteful to predators (think skunk), but according to this source, it is evidently not distasteful to man...so, SCIENCE! Somebody taste tested snail slime. Good job, that person's parents. Maybe birds hate it, even if humans don't, but it probably does at least help them crawl faster - for that iconic, white-knuckled, snail getaway scene, naturally. 

So what's the basis of putting snails on your face? Oh, the things we of the fairer sex do for beauty! Proponents cite the presence of glycolic acid and allantoin, Wikipedia lists hyaluronic acid as well. Glycolic acid you will be familiar with if you, like me, enjoy having a thin layer of your face burned off periodically - for that fresh, chemical-plant-accident look that's all the rage these days. Allantoin has anti-inflammatory properties, and perhaps contributes to the wound-healing properties snail slime is thought to have. Hyaluronic acid is an ingredient in particularly fancy moisturizers.

It's the size of your fist, people. No. Just, no.

I admit that I have no comment on whether this works or is worth it. There is probably some research somewhere, or should be, characterizing the mucus of various species and production methods, to optimize the various goodies contained within. You can even PUT GIANT AFRICAN LAND SNAILS ON YOUR FACE, if you're into that, although not in this country where they are a prohibited species - you know, hugely destructive invasive and whatnot. You probably won't get Angiostrongylus cantonensis as long as you aren't eating raw snails "on a dare". 

References and Miscellany
(1) PLEASE for the love of GOD, someone tell cosmetics companies that the species is not capitalized in binomial names! Every damn bottle of whatever in my cabinet makes this mistake.

(2) And in fact, I have used snail slime in my experiments. Long story short, I was trying to fake snails into thinking they were in a room with a lot of other snails, so I had some Judas snails lay snail trails in a tub before removing them, giving the remaining snails the impression that the room was more crowded than it really was.

(3)  BT-dubs, have you guys heard of this thing called Kombucha!? It's amazing because it's totally alive, just like me!

(4) Thank you Mme. Pollero - I actually can understand more of these than I expected!

(5) Some people do eat marine snail, queen conch. But between the shells and the meat, it's an astoundingly overfished species - not recommended.

(6) Whatever emotions humans conveniently project on these creatures to make ourselves feel better even though 100% of the rest of the time we consider them as good as rocks. And don't get me wrong, I'm not arguing that this handling of snails is cruel, certainly not worse than things we do to the food we eat. I suspect the poking treatment seems "kinder" because it's a small group of women sitting around chatting in a room while handling one snail at a time. The women sure are relaxed, so presumably the snails must be also. But the stainless steel of the shaking treatment makes it look industrial, which I guess it is, but that probably doesn't matter to the individual snails.

Friday Fluff #3: For When Enough is Enough

Thing the first: Thar Be Snail Ogres!

Does this look like a beautiful lady to you?
What is the DEAL with sailors?!
Image by Toriyama Sekien via Wikipedia

I'm sharing a cool Echinoblog post I found in the only way anyone finds anything these days - Twitter. In time for halloween, Christopher Mah describes the mythology of and actual inspiration for several Japanese monsters. This being a Mollusc-centric blog, I will feature the Snail Ogre, Sazae-oni, here, which somehow transfigures into a drowning woman, or something convincingly enough like it to attract sailors, who become the snail's next meal. The real snail this legend is based off of is the horned turban snail (Turbo cornutus1). This image also reminds me of Aku.

There are a number of other monsters on there that are worth checking out and attempting at Halloween costumes, such as the Samurai crab, and/or Stephen Hawking, and the internet darling of the year, the dumbo squid.

Thing the second: Killer Whale Espionage

Because you know you want a giant orca photo...L94 and her baby nursing in BROAD DAYLIGHT! She's not even using a blanket, how indecent! Photo credit: NOAA Fisheries, Vancouver Aquarium

The world is all atwitter, quite literally, about the use of drones in research of the Southern Resident Killer Whales. I've blabbed about some of the recent population growth of this group (here), and there have been even more calves born this year. NOAA just released a video podcast show-and-tell of some recent photos obtained via hexacopter. The contraption, which is strapped to two pool noodles for flotation, flies above the whales to get good pictures of them without disturbing them. They can ID and measure the whales to track growth rates.

Surveillance photos indicate that the babies keep on coming (welcome, Baby L-122!), and the hexacopter provides insight into family life of the growing pods. This year has been a good year for the whales, lots of babies and seemingly well-fed whales. Hopefully that trend lasts.

Thing the third: See Slug Day!

Yesterday was Sea Slug Day! I don't really even have that much to say about it, except that it's worth trolling #SeaSlugDay for the photos, but don't say I didn't warn you that it was a black hole of a time suck! You sort of start to wonder if this group isn't really just an alien race living among us. Or we are a prison planet for all of some other planet's criminals: what with kleptoplasty, and kleptocnidae - they're evidently really just into stealing things, evidently.

Super cutie: O. muricata on E. pilosa

As an undergraduate, I did research on what is the least colorful species in the most colorful group of organisms in the world - Onchidoris muricata. That doesn't mean it wasn't charismatic! I was researching whether this tiny white blob, which you would be well within your rights to assume was some previous beach walker's snot rocker, was interested in eating an invasive bryozoan(2), in the Gulf of Maine. The bryozoan, Membranipora membranacea, was super abundant there, growing all over rocks and kelps. We gave the snot rocket nudibranch a choice between it's presumed preferred food (a native bryo Electra pilosa) and the new bryozoan (which they are probably serving at that gastro street-food from around the world fad place down the street from me), and found that the slug preferred to eat the fancy new food, and could eat it faster.

This was back in 2004, when we wondered, what could this mean for future slugs? Just this year, people are starting to think about whether invasive species are good food for native species - they could be right? Well it turns out that in a lot of cases, they are often beneficial as a supplement to a balanced diet, so they don't harm native species. But on their own, they aren't as good as the diet the predator evolved to eat. So, no you can't have Doritos for breakfast, lunch, AND dinner.

Phew, for Friday fluff, that really was some academic non-sense I just prattled on about(3)! Here's a palate-cleansing video... 

Check out this video I found in my archives. Marney Pratt, my Advisor on the project, grew some bryozoans onto a microscopes slide, and fed them a red algae so that they would show up clearly against the background: the red dots you see are individual bryozoans, called zooids. The big white blob is a single Onchidoris, and you're looking at it from beneath, through the side of a tank and the glass slide. Marney filmed this time lapse of the slug eating a single zooid. If you watch closely, there is one zooid that gets slurped out of its little house toward the bottom right. This is sort of like how an oyster drill (predatory snail) consuming an oyster in that "sucks-his-guts-out" is still an applicable description.

SEE! I told you they were charismatic!

References and Miscellany

1. For Turbo Corn Nuts see disambiguation.
2. Bryo (= moss) zoan (= animal). These are colonial organisms that do really cool defensive stuff...maybe some other day though...
3. But if you weren't completely deterred, you could read the paper we (/Marney) wrote here.

Carcinus, and the Amazing Technicolor Crab Shell OR Video Games for SCIENCE!

I think most people assume that reading scientific papers is totally boring, and that only someone who is really fascinated in some completely arcane microdiscipline could possibly get anything out of it. I wish I could disabuse you of that assumption, but, by and large, yeah, they're pretty boring unless you really get your jollies reading about "A framework to assess evolutionary responses to anthropogenic light and sound"(1). There are certainly some notable exceptions, mostly when scientists, some more successfully than others, try to demonstrate they have a sense of humor(2). But what I like is really digging to find the hidden gems in papers.

Today, for instance, I learned that, "Humans adopt a similar search pattern to birds…when looking for prey on a computer screen". Huh! Did you know that? I did not know that! And, naturally, there are citations!(3)

Sooooo, why do I need to know that? (4) Because it turns out it's easier to get humans to play a video game than to get birds to do what you want - such is the way science actually gets done.

OK, but that's really a methods question, let's get to the point of the paper:

Carcinus maenas just can't decide what it wants to wear. Images from Stevens et al. 2014

The above photos are ALL ONE SPECIES (SRSLY), the European green crab, Carcinus maenas. Notably, this species is regularly listed as one of the worst invasive species on the planet, but that really doesn't have anything to do with this variation in color(5). And it turns out this is not the only species to have this insane catalogue of costumes that undoubtedly drives undergraduate zoology students insane: Also sporting coats of many colors:

• Cancer productus (Red rock crab) native to Eastern Pacific Ocean(6)
• Hemigrapsus oregonensis (Hairy/Green/Yellow/Oregon shore crab)(7)
• Cardisoma guanhumi (blue land crab) from Brazil(8)

Then what is the deal with all these fashion-forward crabs? Well some intrepid volunteers in Singapore attempted to test the hypothesis that the variety of colors helps camouflage crabs when they are young, to keep them from getting eaten by their main predator - you guessed it, shorebirds(9). So this is where it's important to know that humans and shorebirds look at a computer screen similarly, because these volunteers got to play video games - FOR SCIENCE! 

Before we get to the shoot-em-up part (pew, pew!), let's dive into the question a bit more. First off, a quick straw poll, when you hear the word camouflage, what image pops into your head? I'm going to go out on a limb and guess it was something like this:

Out on a limb FTW! Their frowns are the best.

The camouflage that we often think of, that is literally embodied by the chameleon, is called background matching. Which sounds pretty straightforward - trying to hide by pretending you aren't there. But there is another type of camouflage that you are probably familiar with, and it looks like this:

Yes, this is also camouflage, it turns out.

This is called disruptive coloration. This type of camouflage isn't about avoiding detection, it's about making it hard for someone who wants to eat you to figure out just where you start and where you end. You can see how it works really well when you get a dazzle(10) of zebras together and your eyes start to cross, but it also works when a zebra is by itself, at least theoretically. By creating false edges and boundaries, this coloration makes it more difficult for the edge-detection software in your brain to identify and track the animal as an individual. Not convinced? Try this thought experiment. In disruptive coloration, high contrast is an asset because the strong difference in brightness between the white and black stripes overpowers or distracts the brain from detecting the weaker differences in color with the animal an its background(11). 

So let's bring it all together:

Video Games + Camouflage + Green Crab

This paper just came out in Current Zoology (by Peter Todd and colleagues) using video games to test how these white spots might contribute to camouflage in green crabs. They did this by creating fake crab shells and putting them on fake backgrounds, and having students come play their video game, which I'm calling "Nab the Crab", timing how quickly they could find the fake crab shell on the computer screen.

The researchers varied the shells and the back ground in different ways - testing several aspects of camouflage. Here is some really compelling evidence that you can learn something from video games:

Figure 6. from Todd et al.: This is how long it took game players to find the simulated crab shells (examples on the bottom).

On the far right, notice that the game players found the plain shell in no time flat (about  1 second!) - the plain shell is clearly no good at hiding this fake crab from shorebirds (because remember the thing from the beginning about visual search patterns...). Next look at the left two bars, those two shells had large spots on them, but one (LE) had large spots overlapping the edge of the shell, while the other (LI) had the spots all inside the shell. Game players were MUCH faster finding the crab when the spots were all on the inside of the shell (15 versus 33 seconds). The same was true for middle and small sized spots, but the difference in speed was less.  This is all great support for the fact that spots at the end of the shell could act as disruptive coloration!

Figure 1 from Todd et al. High and low contrast spots.

The researchers also tested whether increased contrast would help, so they made crabs with bright white spots and crabs with grey spots, and in most cases, the higher contrast crab was harder to find.

 

Figure 2 from Todd et al. Background.

Of course all of this depends on your background, and some of these effects of camouflage depended on what kind of background the crab was on. If you imagine that these crabs like to live on beaches, you can imagine these backgrounds as small pebbles (on the left) and larger cobbles (on the right). In general, game players took longer to find the crab on the small/pebble background regardless of where the spots were on the shell or what color they were - this makes sense, a busy background makes it harder to detect pattern if the brain has to do a bunch of work interpreting the busyness.

Which is all to say that humans playing video games is only very slightly similar to the process by which natural selective forces of predation by shorebirds might have altered the frequency of shell coloration in Carcinus maenas. Nevertheless, I'm all for video games for science. I found Smorball this summer (Go Piggers!) - by playing you are helping digitize the library of biodiversity literature! I also went on a few virtual safaris, one in Gorongosa National Park, and one in Samburu.

So next time you're caught goofing off playing video games, you can just just say you're doing science like a shorebird. 

YOU'RE WELCOME

References and Miscellany

1. A title I literally just pulled out of the latest issue of Trends in Ecology and Evolution, THE most important ecology journal published, but it sounds kind of interesting, don't you think?
2. This is perhaps the most inscrutable example known to man.

3. But salient to this quoted sentence is Jackson et al. Behavioral Ecology 2005

4. Also, who is adopting who's search pattern here?!

5. You'll hear more about this later, after years of trying to work with this species, I have finally found my way to a project on European green crab.

6. Krause-Nehring et al. 2010 Zoology (link)

7. Rachel Folz (link)

8. Silva et al. 2014 Braz. J. Biol. (link)
9. There is a method to my madness.
10. A group of zebras can also be called a "zeal" but "dazzle seemed more to the purpose here. 
11. Now, I should point out, the story of zebra stripes is probably more complicated than disruptive coloration, and an apparent sudden urgency of solving the "how the zebra got its stripes" question has resulted in new theories, including insect avoidance and keeping cool. I'm going to suggest that stripes probably have multiple benefits for zebras, and might have all played a role in their evolution. I use them as an example because they do make my point about disruptive coloration.