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.

Yellow-Bellied Snails OR MORE SNAIL MAIL!!!

Ground Control to Major Emily.

Yeah, Ground Control. Go ahead.

Uhhh, you still doing science out there, Major Emily? 

Sorta, Ground Control. It's complicated.  

...


Well here's some snail mail. New arrivals from Georgia (Fig.1)!

Figure 1. I do declare! Southern snails! We share a love of sitting on the porch drinking mint juleps.

These snails just completed an amazing transcontinental voyage (and, boy, are their arms tired! Just kidding, they don't have arms). Like other molluscan mavens of aviation described on this blog, these guys know how to travel in style - which is to say in a plastic bag, in a cooler, in a box. These are Atlantic Oyster drills from Savannah, Georgia, which are being temporarily re-homed in quarantine in Washington State(1) while they await their opportunity to teach Science amazing things about assessing risk in new situations.

You might recall the Christmas-that-Emily-Ruined Special(2), well it turns out this is the snail I was actually talking about. When I collected this species from the invasive population here in Washington (Fig. 2), those snails stopped eating and hid when they smelled chemical cues from their injured friends - they didn't even need to smell the crab that was eating those friends. They just knew that something was wrong and beat it out of there. It turns out this response is common among invasive snails here, but not seen in native snails(3).

Figure 2. The author, ca. 2009, collecting invasive Urosalpinx cinerea from Long Island, Willapa Bay, WA.

So the question becomes, are these snail species better than our local native snail species at becoming invasive because they listen to their friends when their friends are in danger? That is, do the snails back at home, in Georgia and Massachusetts, also run for their lives when they hear their friends calling for help?  Or, did the pioneer Atlantic Oyster Drills, who left their cozy homes almost 100 years ago on a railroad car headed west to an unknown destiny, in search of a land of endless undespoiled mud to roam, act basically the same as our local native snail species, and natural selection has changed the behavior of the population.  It's possible that the snails that were, quite literally, dumped from the railroad car on arrival, were all basically clueless about the predators in Washington, but some of the snails in that group did run and hide when they heard their friends calling for help when the native predators did attack - and that those snails were the only ones that survived out of the initial emigrees. They were the only ones who could reproduce, and now we have a population where that is the default response.  

Was the invasion caused by snails that listened to their scared friends, or did it result from the invasion that we now have snails that heed the warnings of other snails?

Yellow-Bellied Snails: Invasion Drivers or Survivors?

Since no one back in the early 1900's thought to do the same experiments I have done on the source populations for our invasive snails, and because the logic of time travel makes my head hurt, I'm going to do what is called substituting space for time. If we assume that there has been relatively little change in the Georgian and Massacusettsian (?) snails in the last 100 years(4), we can compare modern east coast snails (in skinny jeans, on their iPhones) to the invasive west coast population. We would predict not only that the Washington population would be more passive-aggressive, but also that they would respond similarly to the east coast snails if running away from cries of help is an invasion driver, or they would respond differently if running away was a trait that was only helpful in the new Washingtonian waters.

Ergo the snails from Georgia, now to keep my fingers crossed that the Masshole snails will make an appearance.  

Fig. 3. Snails from native and non native populations could demonstrate a variety of hypothesized responses that may or may not be related to their native culture and geographic origin.

References and Miscellany:
(1). Don't worry folks, I've got a permit and a lot of bleach and I know how to use 'em.
(2). Specifically Act II, Scene 1.
(3). More on that at some point - it's not really ready for showtime.
(4). This really only applies to the assumption that the selection for response to injured conspecifics hasn't changed, of course there have been other changes. If there have been, for instance, predators that have invaded on the east coast (cough cough, european green crab, I'm looking at you) east coast snails might also have evolved a strong response to injured conspecifics by the same mechanism of the snails that are invasive here. Actually, now that I think about it, that's one good reason to compare snails from both Massachusetts (where the Green Crab has invaded) AND Georgia (where the green crab has not invaded)

Shameless Serial Promotion OR Lay off, man, I've been busy!

Figure 1. Simbeliebers

I just went to visit my two year-old niece on the East Coast, and when I showed up, she was so excited she ran figure eights around the kitchen table and island (I wish I had an animated gif to add here, but you can probably just imagine one). On the plane home, belted into my own personal 9 cubic feet of space inside a floating tin can, I felt driven to similarly unconstrained expressions of excitement and over-stimulation when I read Dan Simberloff & Co.’s recent TREE review on the current role of invasion science.  Thankfully for my own dignity, nothing squelches feelings of unbridled joy quite so much as sitting in the back of an economy airline cross-country flight (Thank God and Bose for noise-cancelling technology).

So I wrote a li'l piece for the Graduate Student Blog Biodiverse Perspectives.

Enjoy!

Christmas Present #2 OR Red Rock Crabs Rampage

About this time last year, I found out my first paper had been accepted.  Today, I got my second academic Christmas present (hint: it's not a pony, either).

My second, and final, paper from my Master's work was published today in PLoS ONE.  

Woohoo!

That means it's open access, and you can download your very own copy for free!

If you prefer to read my editorialized summary in a more...engaging?...voice, I wrote a little thing for SciPos, UW Biology's Grad Blog. 

Holy Propagule Pressure, Batman! OR Blow Torches = Relief

Well, I don't know about y'all, but I sure was holding my breath while I was reading the first half of this from the Huffington Post.  

Figure 1. EEP!  A dock loosed from Japan as a result of the tsunami just mosied 

up a beach north of Newport OR, all laden with sea life. Credit: AP.

Then I got to the part about blow torches and felt much better.

In invasion ecology, "propagules" are the individuals of a non-native species that are first released into a new habitat.  Increased propagule pressure (more individuals released or more introduction events) is one of the only reliable predictors we've found of whether an introduced species will become invasive.  That, and whether a given species has become invasive in other locations.

Among the HALF TON of non-native sea life affixed to this dock was Undaria pinnatifida (AKA Wakame), invasive in southern CA, along with, "a small crab that has run wild on the East Coast, but not shown up yet on the West Coast" (very helpful HuffPost, thank you).  

So, I admit feeling relief when I got to the part about blow torches.  

But beyond generating concern over Oregon's coastal habitats, having the shrapnel arrive on our own doorstep is a good reminder of the damage done by the tsunami, and that Japan is, of course, still very much in recovery.  I don't know about y'all, but I'm taking a moment to think on that.

Location, Location, Location!

How great is Washington State?! Srsly. Pretty, pretty great.

This was originally posted by Mother Nature Network.


First the good news:

Fig. 1.  Way to go Washington, so redelicious! Kind of phoning it in Wyoming,
don't you think?  Did you really even have to try to win that one?

Then the better news:

Fig. 2.  Dang, Washington, you invaded! Also, Michiganders!
Get with it and EAT THE CARP!

HA! It turns out I live in the best place in the country to study invasive snails! Ima go do that, right now, or maybe just wait til Monday when the tide is better.

Species species of the Week week #2 OR Emily's FAVORITE Tautonym

Gemma gemma

(The Amethyst Gem Clam)

As it's at least supposed to be a molluscan marine blog it seemed worthy to start (1) with a redundant local marine mollusk.  Unfortunately, it turns out that very few, if any, tautonomical invertebrates are native to the Pacific Northwest (2).  So why not a non-native? It turns out this one is also my very, very favorite tautonym.

Figure 1. Peterson (of field guide fame) refers to G. gemma as, "a handsome ... clam, easily overlooked because of its small size".  Just so, sir.  Just so.

Photo Credit: Fisheries and Oceans Canada. Melissa Wong.

In addition to being the name of my wireless network, Gemma gemma (3) is the diminutive Amethyst Gem clam (Disambiguation).  These tiny bivalves are native to the east and Gulf coasts of North America, from Nova Scotia to Texas. They were introduced along the west coast of the US around 1960, but have only recently become very abundant in San Francisco Bay - but hey, what hasn't these days?! Am I right, folks?! (<---- NOTE: That was an excellent/horrible invasive species joke.  Insert rim shot here ... plz.)  

But seriously...

Ted Grosholz (UC Davis) tried to figure out why the gem clam population didn't really take off until decades after it was actually introduced (4).  It looks like the gem clam populations used to be held in check by competition (Figure 2) with native clams of the genus Nutricola (which I'm pretty sure are referred to as "Nut" clams).  

Figure 2. Schematic depicting San Francisco Bay pre-Green Crab Invasion (5).  Native Nutricola spp. (Pink, Yellow, and White individuals) originally kept non-native Gemma gemma (Green individual) at low abundances by eating up all of the food (phytoplankton represented by dinoflagellates, chain-forming and pennate diatoms and coccolithophores) leaving only scraps for poor G. gemma. 

Gem clams were kept at such low abundances that they were not, apparently, worthy of much notice or concern.  That is, until the arrival of the [non-whimsically named] European green crab, Carcinus maenas, which came to SF bay as a stow-away in the late 1980's.  The invasive crab, embracing the gastronomic culture of its host country, prefers to eat the biggest thing is can get its little green claws on, which in SF bay is the native Nutricola spp. The tiny gem clams get overlooked - lucky Gemma gemma devils!  That means no more selfish native clams hogging all the delicious phytoplankton (Figure 3)! Time for tiny gem clams to make tiny gem babies! 

Figure 3. My, how the tables have turned!  Schematic representing San Francisco Bay post-Green crab invasion.  Crabs (lower left) preferentially consume native Nutricola spp. (lonely yellow individual), freeing up more food for non-native gem clams (prolific green individuals) to make gem babies! 

Cool, huh?!  In many cases like this one, non-native species are present at low abundances for years after they are introduced, leading people to be all like, "ohhhhhhh....whateverrrr...it's no big deallll...I mean, who cares about some dumb clam anyway..."  And then something changes.  Maybe the non-native population develops a key adaptation that enables it to make more babies than before, or something else in the environment frees up resources (*cough, cough* I'm looking at you C. maenas), and the population of the non-native explodes and messes things up for EVERYONE.  And people are all like, "whaaa!? But how could we have known!?"  And I'm all like, "because it happens every time!"  Well, not every time, but surprisingly often. 


So called "lag times" are a pretty common property of biological invasions, and one extremely good reason that, notwithstanding any aesthetic arguments(6) for the moral equivalence of human and non-human invasions, all introductions of non-native species deserve to be treated with caution. 

References and miscellany:
(1) Yes "start" more than a month later, this is the first second species species of the week week. I did warn the one of you that reads this that these would be irregular and unlikley to actually appear on a weekly basis.
(2) I'm tempted do some arm waving here about how this probably has something to do with the idea that the tautonym species are so-named because they were the first of the genus to be described, and most of the marine genera in the PNW were first described in Europe or the east coast of North America.  But that arm waving will only appear in small print in the foot notes.
(3) On the pronunciation of Gemma gemma: "gemma" comes from Latin for "jewel". I assume it SHOULD be a hard G if you're being true to Latin pronunciation, but I have only ever heard it pronounced with a soft G, presumably in honor of the common name - which also pretty much comes from Latin for "jewel" but has since been bastardized.
(4) Grosholz, E., (2005) PNAS. 102(4): 1088. 
(5) If you have to look this game up, and don't have age as an excuse, your childhood was misspent.
(6) Drew Christie is a great Seattle animator and illustrator whose work I actually really like, but this piece got under my skin (really really far under my skin), for making a tenuous aesthetic (but it's cute!) and moral (humans are invasive too, who are we to point the finger?!) argument that manipulates feelings about a legitimate conservation issue.

Scientistas of the World Part II OR More Swoonage

This post closes the loop on my promise to write about TWO Scientistas back in October for Ada Lovelace Day.  Get off my back, man, I said I'd do it!  Just kidding, absolutely no one but me is actually concerned about whether or not I write this post.  Except maybe my reader in Russia! Google tells me that I have three views on Rah Rah Radula from Russia.  Probably it's just someone phishing for my credit card number.  They'll probably succeed, but in the meantime maybe learn something about snails and science.  SUCKERS!

Part II: Sharon Strauss and More Swoonage

So, recalling that Ada Lovelace Day is all about inspirational women in STEM fields, I'd like to call your attention to Sharon Strauss.  Now, I have a bad habit of letting my first impressions get the best of me.  I first paper-met her  when I read a review she wrote with colleagues at UC Davis about how native species evolve in response to introduced species.  This is undeniably a cool topic.  To give you just a taste of what's going on out there:

Witness the Black Snake of Australia

Figure 1. Witness! Are you Witnessing? You better be! This handsome devil,
helpfully demonstrating "gape-limited predation" is Pseudechis porphyriacus. 

The Black Snake, Pseudechis porphyriacus, is native to Australia, where it preys on anything smaller than it's head (witness Figure 1), rodents, amphibians, whathaveyou. Wait did I just say amphibians?! In Australia?! That's right, Ima talk about CANE TOADS!!!  For those of you who haven't watched the never. -ending. parade. of documentiaries. about this particular poster-child of biological invasions, cane toads were introduced to the continent-cum-island to control cane beetles in 1935. The beetles were accidentally introduced earlier and were problematic for the sugar cane growers.  Folks thought the toads (incidentally Bufo marinus) would solve their problem by eating the cane beetles.  But toads found everything else in Australia much tastier.  So cane toads became super abundant without solving the beetle problem.  In addition to eating everything except what they were supposed to, they also killed native things that ate them, because they secrete a toxin (witness Figure 2) when they are threatened or have road rage (it's ALL about inducible defenses people!).

Figure 2. Oh gross, that white stuff is bufotoxin and this toad is MAD!

So black snakes were eating cane toads and dying from actual food poisoning. But!...BUT! It appears that in approximately 23 generations of snakitude, this species has not only evolved increased resistance to the toxin (Phillips and Shine 2006), they also have evolved smaller heads (Phillips and Shine 2004).  What?! Smaller heads?! That's dumb.  No, smaller heads for a gape-limited predator means you can only eat smaller toads.  Smaller toads make less toxin.  Pinhead snakes eating small toads live to pass on their pinhead genes to the next pinhead generation. EVOLUTION: WIN! 

Anyway, that's way cool, but let's get back to the point

Shocking Upshot: I got really excited about this paper and this concept. Evolution happens so fast, and humans can cause it and we can see the effects!  So, naturally, the author was elevated to Science Goddess status.  But my hasty opinion of Sharon Strauss was formed on one paper only.  Last spring, as part of an ecology seminar, I reviewed and presented on a larger portion of her corpus, and you can imagine how much higher Sharon rocketed in my esteem (hint: way higher) when I realized how broad her research was (hint: pretty, pretty broad, witness the breadth of Figure 3).

Figure 3. Portrait of Sharon Y. Strauss and Friend.

In addition, and I wish ESA hadn't removed or archived this information because it will not have the same impact if I just tell you about it, she wrote this great piece in a profile about the joy of doing science that serves our curiosity.  Or at least that was what I took away from it, so it's entirely possible I'm getting this wrong or projecting.  I'm pretty sure it was something along those lines anyway.  My point is that my perception of Sharon Strauss is that she approaches not only the content of science thoughtfully, as demonstrated by the strength of her research program, but also the act of doing science, the living of a scientific life, of training more scientists.  If that sounds a bit grandiose, that's because it's how that makes me feel.  This is, I think, how we all start out, as scientists and/or students, but something we quickly lose sight of when we get bogged down in logistics of funding and politics of publication.  Or even before then when we have to cram so much knowledge into our heads because we are studying for qualifying exams and trying to remember why we thought this was a good idea in the first place and what do you with all this information that you don't have a context in which to place and didn't I learn all this before and why don't I remember it, it's a good thing I'm learning it now because I'll definitely remember it this time NO I'll never remember it it's too much and I don't even know what they're going to ask me I will definitely embarrass myself horribly in front of my committee and my life will be OVER!


...


OK. So that happened. Sorry.


Like many other passions one turns into a career, you can at least imagine how one might lose track of why one does Science when one is panicked about doing Science very well.  For me, Sharon Strauss was a timely reminder about big-picture thinking.  Inspirational scientists (and all scientists for that matter) aren't only about good science - lots of people do good science.  They are about doing good science with grace and generosity.  

Eat the Carp! OR Invasion semantics

My friend Nick sent me a copy of this, which is currently displayed in the National Archives as part of an exhibit on  food.  Released by the US Department of Commerce in 1911.  I love ancient Swedish recipes!

This blog is all over the place!  Today's digression is non-native species, which is really not so much a digression as my meat and potatoes - freal, I don't eat meat, but potatoes (family: Solanaceae) are native to the Andes.  

Non-Native "!=" Invasive

I'm a nerd, but for those of you who are normal, "!=" is code for "not equal to".  I told you.  Anyway, saying "non-native" instead of "invasive" all the time is admittedly cumbersome, but I am nothing if not a champion for precise language.  Not all plants and animals that are transported to new places become "invasive".  That is not all of them manage to make it through:

The Four Stages of Biological Invasions ... OF SCIENCE!

1. A species gotta get from A to B to invade B.  If you're a pluteus (Geshudheit! Thank you!), you might hitch a ride in ballast water of a commercial ship moving cargo between ports. If you're a starling, you might make friends with an acclimitization society or Shakespeare. But almost invariably, you will need humans to help you move to a new place.

Get on the bus, pluteus! (Pluteus = baby sea urchin)

2.  Species gotta make their way in their brave new world.  If you're going to be a good invader, you need to be able to find food and ultimatley make lots of new baby invaders to help you invade, otherwise you're on your own.  Here's hoping your new home is just as cozy as your old one!  If you're a real goldilocks, and everything is just too hot, or too cold, or too salty, or too nitrogen-poor, I hate to break it to you, but you're just not going to be a good invader.

3. Now starts the conquering! If you've made it through the first two stages, good on ya, now comes the fun part: GO FORTH! SPREAD! Expand your range! Conquer new territory! The world is your oyster!  Often, in the case of invasive species is this literally true.  Charles Elton was a rad old school ecologist and one of the first to think extensively about species translocations.  Way ahead of his time he said,

 “The greatest agency of all that spreads marine animals to new corners of the world must be the business of oyster culture.”

DUDE! You didn't even know how right you were Dr. Elton! No, you probably did because you were absurdly smart.  I may have told you this story already, but when oyster growers used to bring oysters to new areas to try to expand their market, they often just ripped up big chunks of oyster bed and ship it across the country/ocean/etc.  If you've ever spent 5 seconds on an oyster bed, you know how many other things hide in the spaces between oysters.  So these folks also unintentionally moved lots of other critters with the oysters.  It's a sweet deal for these critters, because not only do they get their home (oyster reef) moved with them, they also get humans to take care of their home for them!  And then when you're ready, you can light out for the territory and conquer new oyster beds and other habitats!


4. Mess some $%!^&* up! Now is your chance to eat whatever looks good to you in your new home, and force other native inhabitants to leave theirs.  Take what you want, leave a mess, and NEVER APOLOGIZE!  It's just your survival imperative that compels you to wreak havok (hmm. This sounds a lot like the MO of western civilization, but that is another conversation for another day). If you are to be an ideal invader, you will find some way to cost humans money.


So the point is that not all introduced [non-native] species become invasive.  In fact - very few do.  It turns out it's kind of hard to survive 20 days in a dark ballast tank and many don't make it.  Of those that do, only a few ever manage to establish self-sustaining populations once they arrive. Even fewer are able to expand their range: gardeners will tell you how frustrated they get trying to keep their non-native plants alive. 


Interestingly, there are many that do meet all the criteria to be considered "invasive", but we like them anyway, so we don't want to hurt their feelings by calling them names - Pacific oysters, for example.  They're not native to the west coast of North America, but they were introduced to start a fishery for them here.  They spawn liberally (hippies!) and have established reefs "in the wild".  They can outcompete rare native oysters (Buhle and Ruesink, J. Shellfish Rsch 2009) but we still like them because they are commercially valuable.  So we call them "non-native" because it's true but sounds less judgmental.  


Don't get me wrong: Semantic "!=" Trivial


But here's a species that is, without a doubt, invasive:


Featured Invader of the Day: Asian Carp!

Look at 'em go! Asian carp are super-abundant in the Mississippi River

There are several species of Asian carp that have made it through the gauntlet, and are considered invasive in the US. Here's how they did it:


1. Be introduced (Check): Imported to the states for aquaculture. *Maybe* escaped during floods and hurricanes in the 1990's (apocryphal)


2. Establish yourself (Check!): Made lots of babies in the Mississippi river (see picture above)


3. Expand your range (CHECK!): Are spreading upriver toward the Great Lakes, terrifying the good folks of those waters to such an extent that electric barriers have been erected to keep them out.  But DNA collected from the waters above the barriers indicate that the fish keep on busting through!


4. Impact the environments and human enterprise (Check): Probably outcompete other native fish by being very big eaters.  They eat so much plankton, there's not enough left for other fishes.  ALSO, they are evidently a safety hazard to boaters.  Anyway, people dislike and want to get rid of them.

Eat the Carp!