In Defense of Parasites

Parasites have it tough. They’re usually ignored, and when they are mentioned, it’s never positive. They’re repulsive primitive creatures that are an annoyance at best and terrifying at worst. At the end of the day, they’re just marginal players at the edge of an ecosystem, and can probably be ignored.

True, a parasite worming its way into a host may not be quite as awe-inspiring as a crocodile seizing a hapless zebra in its jaws. But that doesn’t mean it’s any less ecologically important. My fiancé Matthew and I went on a bike trip near Walla Walla recently, where we saw a white-tailed deer. However, that was the only wild ungulate we saw – no other deer, no moose, no elk, nothing. We didn’t just get unlucky. Around 80% of white-tailed deer are infected by a parasitic nematode (Parelaphostrongylus tenuis). They can survive with it without too many issues. But if the nematode makes its way into other ungulates, it causes severe neurological damage, usually killing the host. Because of this, on a local level, white-tailed deer habitat practically never overlaps with other ungulates. We didn’t know it at the time, but our bike trip – and the whole ecosystem we traveled through – was shaped by a humble parasite!

If it wasn’t for P. tenuis, these hills could’ve been full of all kinds of hoofed critters!

To really understand how parasites work, you need to think like a parasite. And if you’re a parasite, you’ve got a pretty tough life. Your hosts are your only possible habitat, islands of safety in a vast, vast ocean of death. Your odds of making it are maybe one in a couple million. So naturally, you want to improve those odds, even if by just a bit. And you’ve got two main options. There’s the usual evolutionary path – modify your body or your behavior. But since their environment is a living being, parasites have an interesting alternative option. They can modify their host.

That first route may not be unique to parasites. But they have found some ingenious paths to take. As an example, let’s look at some freshwater mussels in the genus Lampsilis.

That weird-looking flap kind of looks like a minnow, right? Well, fish sure think so. They see an easy meal, but as they swoop in for the kill, those lips open up and spit a cloud of larvae in its face. Those larvae attach to the gills of the fish, where they have an easy meal and a safe home as they mature.

For the parasitic flatworm Dicrocoelium dendriticum, tricking a potential host isn’t enough. In fact, just one host isn’t enough! This particular species has to find a way to get from a terrestrial snail into an ant, and then from an ant into a sheep. To do that, it employs a bit of trickery and a bit of manipulation. It starts in the snail gut, where it gets released from the snail in sugary slime balls. Ants are attracted to the sweetness and obliviously munch away. As the parasites develop in the ant, one migrates into the ant’s brain, and something strange happens. That evening, the ant develops an uncontrollable urge to climb. It makes its way all the way up to the very tip of a blade of grass, and waits. As the sun rises the next morning, the urge fades, and the ant descends to feed and work. This repeats for a few days until an unlucky sheep swallows the ant along with a bite of grass. From there, the flatworm matures in the sheep’s immune system, ejecting its eggs out to infect a snail and start the whole cycle over again.

We’ve seen parasites that can trick their hosts, and ones that can change their host’s behavior. But some can go even further, and change their host’s appearance. Even better, they tend to be parasites of our favorite critters – crabs!

Rhizocephalan barnacles are the leather-jacketed rebel of the barnacle world. They aren’t content to stay put on a rock and feed on plankton. They have their sights on much, much bigger prey. Crabs. An infected crab will have a big, obvious sac, usually under its abdominal flap. And inside, the parasite creates a long, tangled root-like network through the crab.

That big white thing is the barnacle (this one’s Sacculina carcini)
A rhizocephalan inside the hermit crab. The external portion is orange, the internal is green. From Noever et al (2016), which is a great read

Now, the rhizocephalan isn’t just randomly attaching to the abdominal flap. That’s where females keep their eggs. So if it infects a female, it just forces the female to keep protecting the “eggs” as usual. But what if it’s a male crab? Well, the barnacle has a solution for that too. Just turn the males into females. An infected male crab will see its abdominal flap widen and its claws get thinner. It’ll even start caring for its “eggs”, pushing water over them to keep them oxygenated and healthy. And just like an infected female, when the parasite is ready to spawn, the crab will climb up high and shake its abdomen around as if it’s sending its own eggs out into the current.

Progression of rhizocephalan infection in male crab, left to right. Look at that abdominal flap widen!
From Fahzan et al. 2018

Clearly, parasites aren’t backwards, degenerated, marginal creatures. They’re key parts of their ecosystems, doing far more than we realize to structure the world around us. And they’re shockingly specialized, able to trick potential hosts and deftly manipulate their current hosts. They might be gross, but they’re also worthy of a whole lot of attention.

Postscript: Many of the examples in this post came from Claude Combes’ book “Parasitism: The Ecology and Evolution of Intimate Interactions”. It’s not just a fantastic book on parasites, it’s a fantastic book period – one of my absolute favorites ever. It’s chunky (630 pages without references), but if you really want to dive into the world of parasitism, there’s nothing better.

You know it’s a good book when the figures are like this

– Fahzan H., Waiho K., Wee H.B., Surzanne M.A., Ma H., Ikhwanuddin M. 2018. “Predicting the sacculid Sacculina beauforti infection status of the orange mud crab Scylla olivacea by discriminant analysis”. Aquaculture 491: 128-134
– Noever C., Keiler J., & Glenner H. 2016. “First 3D reconstruction of the rhizocephalan root system using MicroCT”. Journal of Sea Research 113: 58-64

What’s A Crab Survey Like?

A Photographic Journey in the Bering Sea

If you’re subscribed to Google Scholar alerts for “chionoecetes” (as I know you all surely must be), every few days a new paper on Bering Sea snow or Tanner crabs will pop up in your inbox. Today, for instance, I got a paper on how warm and cold years affect lipid storage in these populations! On its face, this might not appear too surprising – hey, it’s just another paper. But each and every paper represents a shocking logistical feat. These crabs are in some of the most remote corners of the globe. To get to them, you can’t just pop down to the seashore – you need at least a week of time and tens of thousands of dollars. Because of this, most of the research relies on annual population surveys performed by NOAA and the Alaska Department of Fish and Game (ADF&G). These surveys typically last upwards of a month, and in 2017 and 2018, I was lucky enough to go!

Snow crab range within the Bering Sea. That red star is Anchorage – the closest place with a population over 10,000. And it’s over 600 miles away!

In August of 2017, I was a technician working on crab research projects for ADF&G. I was fresh out of undergrad, and adjusting to living in the small town of Kodiak, Alaska. Out of nowhere, I was invited to join a survey centered on the blue king crab population near the most remote place in Alaska – St. Matthew Island. I had never been out of sight of land before, and now I had the chance to spend a full month there. Before I knew it, I was on a plane headed to Dutch Harbor to join the crew.

View of Dutch Harbor/Unalaska from the top of Mount Ballyhoo

We had three days there before it was time to weigh anchor. I spent most of my time exploring the town, admiring the abundant wild foxes, indulging in the all-you-can-eat king crab buffet, and in awe of the isolation. We also loaded up the 113′ Sandra Five, our home for the next month. This name raised my eyebrows, but happily it was named after 5 sons – there hadn’t been a Sandra One through Four.

Loading the pots on board
Fully loaded. To get on deck, you walk through the pots!

Soon, we were off. We had nothing to do for the first few days, as we had to go several hundred miles north to the island. But the skies were blue and the seas were calm, so I spent much of it up on the bow taking it all in. And before I knew it, we were hauling up our first pots!

Like most of our pots, not a whole lot of blue king crab, but a TON of snow crab

The days quickly began flowing together. We’d spend mornings sitting around the galley table chatting and snacking, then throw on our gear and head out to the deck. Pots were laid out in clusters of four, with each cluster around 45 minutes apart. Sometimes, the pots would be practically empty, and we’d spend 5 minutes watching the crew pull them before heading back inside and watching ’80s movies on VCR. Other times, they’d be overflowing with crabs, and we’d be out there for hours on end. We’d see all kinds of fascinating critters – basket stars, sponges, sculpins, shearwaters, and plenty more. Before long, we were a well-oiled machine. The crew would dump the pot on the table. As they tied it back into the stack, we pulled aside all the fish, measured the commercially-important ones, and sent them down a makeshift wooden chute back into the sea. Snow, Tanner, and king crabs got carefully measured, and females got checked for eggs. Everything else, we counted and dumped back over. Usually, as we headed towards the next string of pots, we’d have one or two animals we just couldn’t ID – typically a hermit crab or snail, but occasionally an octopus or sea star – and we’d flip through books, debating the finer points of taxonomy.

An Arctic lyre crab taking refuge inside a sponge!
A rose star by any other name would be as pointy

One calm evening a few weeks into the trip, the captain spotted an odd lump on the beach. We had plenty of daylight and our work for the day was done, so he decided it merited further investigation. We all pulled on our gear, piled into the Zodiac, and motored towards the most remote spot in Alaska. As we got closer, it was clear that the lump was the decaying carcass of a whale. But once we landed on the beach, we began to see bones everywhere. Huge spinal columns, half-buried in the pebbles. They had been laying there untouched for who knows how long. Without the usual armies of beachcombers and treasure hunters, whale skeletons littered the beach.

The dead whale that initially drew us in. Ewww.
Just one of many whale bones around

As we got further up the beach, we noticed another impact of the lack of humans. Ironically, its isolation meant its beaches were coated in debris of all kinds. Fishing nets, buoys, bottles, buckets. Even on the furthest reaches of the planet, humanity’s impact is intensely visible. However, even this had benefits. In just an hour, we had already found seven Japanese glass floats, ordinarily, a once-in-a-lifetime beachcombing treasure.

We ended up landing on the island a few more times, though each was far too short. We found the remains of a WW2-era navigation station, the only known intentional effort humans have made to put any sort of permanent settlement on the island. Reindeer skulls were scattered across the lichen, remnants of an introduced population that skyrocketed and then crashed to zero in a few short years. For a few short moments, we even spy a flock of McKay’s buntings. These nimble birds are a startling white, and this small island is the only place they breed. Even the most devoted ornithologists go their lives without seeing one. My interest in birds is always in passing, and I feel undeserving of their beauty. They flit around the rusted carcasses of diesel barrels, their snow-white wings striking against the green-gray tundra

Remnants of the Coast Guard station. Those white dots in the center of the frame are McKay’s buntings!
Some northern fur seals coming by to say hello

Landing on the island was disorienting. My body had grown used to the rocking of the waves, and even on firm ground I felt a gentle sway. Mentally, I was searching for steadiness too. Being on a boat is one thing, but being on solid land, with the knowledge that there likely aren’t any other humans around for hundreds of miles, was simultaneously unsettling and electrifying. We were truly isolated, and in one of the most desolate and barren environments imaginable.

On the way back, relaxing with a book under blue skies

Time gets funny on a survey. It simultaneously seemed like we had always been on the boat and that we had just left. Before I knew it, we had finished our last few stations and the survey was over. St. Matthew Island disappeared in the distance, and I spent the rest of the trip alternating between savoring the last few days at sea and dreaming of all the luxuries of home (long showers! fresh food!). As we docked, I excitedly bounded down the pier, filled with the simple joy of being able to run again. I spent most of the day just enjoying being around other people, but in the back of my mind, a little part of me missed being out on St. Matthew, with just the sound of the wind and birds and the grey fog making the distant cliffs ghostly apparitions as yet another pot of fish and snails and crabs was dumped on the table to be measured and recorded and flung back into the sea.

One of the most beautiful places imaginable


Today, we’ll be chatting about something a bit different than usual! We’ll keep things crustacean-y, but instead of focusing about Alaska and crabs, we’re moving out east and talking lobster!

Picture a map of the US. No, not one of the boring regular ones. One of those kindergarten maps, the ones with cute little drawings for each state. There’s a cheese wedge in Wisconsin, a banjo in Tennessee, some palm trees down in Florida. And up in Maine, inevitably, there’s a lobster. The two are practically synonymous. But only a few decades ago, this wasn’t the case. Over half of American lobsters were caught outside of Maine, with much of that coming from Long Island Sound – just north of New York City!

The fishery had been thriving for decades, and in 1998 it was truly booming. It pulled in $70 million a year (2021 dollars), making it roughly equivalent to the current size of all Alaskan king crab fisheries combined. Hundreds of fishers would go out each day, making their living hauling in pots. Then, over a few days in September of 1999, it practically vanished.

“New Yooooork, concrete jungle with lobsters in mud” – Alicia Keys

July 1999. New York City. It’s a brutally hot summer, one of the hottest in memory. Ambulances race across the city, responding to calls of dehydration and heat exhaustion. Central Park hits 101°F. Out in Long Island Sound, the waters are warming too. And the lobsters down on the sea floor are suffering. Lobsters are adapted to cold waters, and cannot survive temperatures above 69°F. Temperatures aren’t that high, but the lobsters are already seeking out cooler waters. In the shallow basin of Long Island Sound, that means clustering together in the deeper cold pools. Weakened by the heat, they crowd together. Still, they are somewhat lucky – the waters of the Sound are staying stratified, with the coldest water at the bottom. It may be warm down there, but it’s much, much hotter up in the shallows.

Disease rips through the packed crustaceans. Neoparamoeba pemaquidensis, a parasitic amoeba, rapidly spreads amidst the throng. It infects the lobster’s connective tissue, making them limp and sluggish. Worse, many were already suffering from hideous lesions caused by a bacteria that digest the shell of the lobster. A warm spring had caused the lobsters to molt early, leaving them more vulnerable to this shell disease. Few succumb to these two illnesses, but they sap the strength from those infected.

A lobster with shell disease. Ew.
(New England Aquarium)

August 17, 1999. Off the coast of Africa. A zone of low pressure has started to form, and begins to move west. It looks innocuous at first, just another of many tropical waves. But a few days later, near Puerto Rico, it builds into a full-blown tropical storm, and then a hurricane. Hurricane Dennis. It slams into the Bahamas, washing out roads and blowing down power lines. In Florida, high waves slam into the coast, killing four. On August 31, the warm tropical winds crash into the Canadian cold front, producing high winds across Long Island Sound. The water is thoroughly mixed. All that hot surface water is pushed down deep. The lobsters have nowhere to go. This sharp spike in heat pushes them beyond their physiological limit. Already weakened by the prolonged heat, overcrowding, and disease, they die en masse.

You know how when you swim in a pond the water is warm up on top, but if you dive down a bit you’re suddenly freezing cold? That’s stratification. The two dotted lines show that before the wind, Long Island Sound was stratified. The solid line – from after the wind – indicates that after, it was more like a swimming pool, with the same temperature on the surface and on the bottom.
Wilson and Swanson (2005)

Suddenly, people began pulling up traps full of dead lobsters. Then the traps were empty. The devastation was immediate and total. Over just a few days, the fishery practically evaporated. 70% of the lobstermen in the western Sound had lost every dollar of their income within a few months. And worse, the fishery never recovered. Nowadays, it is practically nonexistent. 99% of the lobstermen have gone out of business. Yearly catches are just 2% of what they were in 1998. The once-thriving fishery has utterly disappeared.

Ultimately, the 1999 Long Island Sound lobster die-off was a climate change disaster. The population was already vulnerable, a cold-adapted species at the southern extent of its range. A confluence of unlikely events caused the initial die-off, and then the steadily warming waters have prevented the population from returning to its former levels. And as our planet continues to warm, catastrophes like these will undoubtedly be more and more common. Already, lobsters are moving north nearly 50 miles a decade. In a few decades, we may all associate lobsters with Canada, with the Maine lobster fishery a vague memory.

Here in Puget Sound, we’re just recovering from our own disastrous heat wave that devastated shellfish populations. I’ve been seeing picture after picture of clams on the beach, shells open as if they’d been steamed. It’s a sobering reminder of how climate change has already impacted our marine ecosystems, the importance of our immediate action, and the complete failure of our systems to deal with it. Twenty years ago, a healthy, multi-million dollar fishery utterly vanished. It seems inevitable that in the years to come, plenty of other fisheries will join it.

Clams on the beach killed by the 2021 PNW heat wave.
(Hama Hama Company)

Sources (and additional reading)

The Value of Crab

For such a niche profession, Alaskan crab fisheries have a surprisingly strong cultural presence. Through shows such as Deadliest Catch (now on its 17th season), crab fishermen showcase the rewards of hard work. It’s the classic American tale. Work through sleepless nights in dangerous conditions, push yourself past to your limits and past them, and all that pain and sacrifice will be rewarded. You’ll get a huge paycheck, you’ll work your way up from a greenhorn to a captain, you might even be a celebrity.

From my hometown of Homer, Alaska – we used to have a gift shop dedicated to merch for a single Deadliest Catch ship. Also the best pizza in town next door.

But if you follow the crabs to shore, you run into a crowd of people whose hard work isn’t getting them TV deals, or even a decent wage. Upon returning to port, an army of workers descends on the ship to offload the crab, check each for quality, break them into chunks ready for sale, and place them into boxes for freezing and shipment. It’s backbreaking, monotonous, dangerous work. It’s also extraordinarily valuable – without the work of seafood processors, all that delicious crab and fish wouldn’t make it anywhere near your dinner table.

To get an idea for the difficulty of offloading crab, put two gallons of milk on the floor. Now put them on a shelf at head height. Repeat that around 500 times. Congratulations – with the help of a few friends, you could offload a small delivery from one ship! Of course, in real life, you’re cold and wet, standing in an uneven and swaying hold. The gallons of milk don’t have convenient handles – they’re covered in sharp spines and if you misplace a hand they might pinch you hard enough to cause nerve damage. And after you finish that delivery, you have another, and then another. Let’s be kind and say just another 9 hours.

Though their work requires strength, skill, and tenacity, crab processors get far less than they deserve. Over a 12-hour shift, they take home only $140. Most in the industry work seasonally, but even optimistically assuming year-round 40-hour work weeks, that’s only $24,000 per year. Now, they do get other benefits – generally, housing and food is covered during the season. But “housing” often means staying in crowded, rat-infested dorms with moldy mattresses and raw sewage. Those dirty, cramped conditions meant that processors were hot spots for COVID, with some outbreaks infecting over 75% of workers.

AIG = Aleutian Island golden king crab, BBR = Bristol Bay red king crab, BSS = Bering Sea snow crab,
BST = Bering Sea Tanner crab. Note the difference in scale on the graphs on the right.
Images from this report

Low-paying, physically taxing jobs in unhygienic conditions aren’t desirable for many. But instead of simply offering higher wages, seafood processors typically fly in temporary foreign workers (often from countries that have been politically and economically devastated by US policy) who lack better options. Interestingly, the processing industry hasn’t exactly been subtle about bending the rules with visas. Until 2012, many seafood processors were actually foreign students, with their work legally designated as “cultural exchange”. This creates racial stratification that is particularly jarring to witness. On the floor of the plant, English takes a backseat to Spanish and Tagalog, but upstairs in the offices, nearly everyone is white.

Often, discussions of low pay are met with the refrain that workers should have chosen jobs that were “more valuable”. But what does that mean? Well, let’s look at it from the perspective of the owner. If they pay the average processor $11.85 per hour, then by definition, the processor must be producing more than $11.85 of value (even after accounting for expenses like operating costs). If it didn’t, the owner would have no reason to hire them! That extra value then goes to the owner as profit. And there is plenty of profit to be made – the owner of Trident Seafood, one of the larger processors operating in the Bering Sea, is worth around $1.1 billion. These fisheries are unbelievably lucrative. The problem is, the workers aren’t the ones getting it.

So, what is to be done? How do we fix this obvious injustice? Unfortunately, it isn’t simply a matter of pointing it out – most of this exploitation is entirely legal. And the illegal exploitation that exists (such as rampant wage theft) has no real mechanism for enforcement. Voting in politicians and changing the laws works in the abstract, but politicians are far more answerable to American billionaires than working-class non-citizens. I certainly don’t have all the answers, but when I look at pushes for better treatment of food production workers – both historical and current – I don’t see people asking politely for change. Instead, I see people uniting together and using the power they have as workers to force that change to happen.

We picture the crab fishery as a Bering Sea fisherman headed back home. He’s dead tired, the caffeine barely putting an edge on the dull exhaustion that blankets him. But he’s happy too. He made good money out there, enough to pay the bills and a good chunk more too. When they pull up to offload their catch, he can sit back, relax, and watch the dollar bills be hauled out of the hold. But we ignore the mansions of the owners and upper management, paid for with millions from the labor of others. And we certainly ignore the middle-aged woman up at the processor pulling her gloves over arthritic fingers. She’ll be on her feet for another 12 hours, stacking boxes, cracking open crabs, filleting fish. Despite all her hard work, she won’t make anywhere near a fair day’s pay. As people who are in some way adjacent to the crab industry, we have a responsibility to make sure she gets it.

The Invader That Isn’t

It’s 1989. The Golden Gate bridge looms in the background as Californians calmly go about their day, unaware of the threat that surrounds them. In the water, the invading force waits, building their strength, knowing that soon they can seize the whole coast. This wasn’t a particularly hamfisted Hollywood movie – it really did happen! The invader was just a little smaller than you might think. The European green crab (Carcinus maenas) – a small crab with a voracious appetite – had appeared on the west coast of North America, and had no plans to go anywhere.

The response from the scientific community was swift and decisive. Money poured in to research and understand the nature of the threat. Volunteer citizens monitored their beaches. The European green crab could completely overturn nearshore Pacific ecosystems from Mexico to Alaska, and everyone wanted to stop it. To this day, monitoring programs are still in place all across the West Coast (in Washington State, the Washington Sea Grant Crab Team is usually looking for volunteers!)

In true Cold War fashion, another invader was simultaneously preparing to launch an attack. Seven years later, some Russian fishermen off the bitterly cold Arctic coast of Novaya Zemlya pulled up a few snow crab (Chionoecetes opilio). In the years since, their numbers have exploded and their range has expanded west, through much of the Barents Sea.

That long island in the top right is Novaya Zemlya, which translates to New Land – tells you a bit about just how remote it is!

Rather than alarm, this invasion was greeted by a mix of caution and optimism! While European green crab are inedible (at least usually), plenty of people saw the appearance of snow crab as an opportunity for a new fishery. Monitoring programs were established, but with the goal of managing the population, not curbing its harm. Today, the main problems are political, not ecological. Russia and Norway are trying to monopolize the snow crab harvest, sending diplomats across Europe into a tizzy. Norway projects that eventually, the Barents Sea snow crab fishery could be worth upwards of 300 million USD annually. That’s some serious money on the line.

Not everyone is thrilled about the arrival of snow crab. Their introduction could completely disrupt nutrient cycling and send ripples up and down the food chain – there’s still so much that we simply don’t know about what its impact is and will be! But as of yet, there hasn’t been any major impact on any commercially-important species. And despite those fairly large caveats, that has been enough to deem Barents Sea snow crab a resource to be managed and fought over, not a pest to be eradicated.

A key question: Are snow crab “sedentary”? If yes, they’re governed by the same boundaries as oil and gas deposits. If not, then they’re governed by fishery boundaries. Diplomacy gets complicated quick!

Two invasive species, two completely different responses. Looking at them side-by-side showcases a few things. First, our response to introduced species has a whole lot to do with their impact on us rather than high-minded ideals of keeping ecosystems intact and primordial. And second, each species introduction is different. Some are disastrous, like the cane toad or the Burmese python. Others can be neutral, or even positive to both ecosystems and humans, such as with giant tortoises or honeybees! In fact, many have been calling for us to change the way we talk about so-called “invasive” species – describing them instead with more neutral terms such as “non-native”.

Whether the Barents Sea snow crab introduction will, in the long run, be seen as good is yet undetermined. But for now, the outlook seems positive. And who knows – with some shifts to the American diet, perhaps in a few decades the appearance of European green crab in California will be seen as a welcome arrival, not a terrifying invasion.

Do Tanner crab exist?

After several years of posts on here dedicated to Tanner crab research, this may seem like a ridiculous question. However, the answer is surprisingly complex and not as clear-cut as it first appears.

First, some housekeeping – beginning with this post, this site will be ran by Aidan Coyle. Aidan joined Steven’s lab in the fall of 2020, and has continued with the research began by Grace Crandall on Tanner crab and Hematodinium, now that Grace has graduated. Infinite thanks to Grace for her diligent and detailed data collection, the help she has kindly given me with my work, and the time spent creating this site (the DecaPOD was what got me interested in Steven’s lab)!

Now let’s return to today’s question. To determine what a Tanner crab (Chionoecetes bairdi) is, let’s first define what makes it unique from one of its closest relatives – the snow crab (Chionoecetes opilio).

One of these is a snow and the other is a Tanner. Can you tell the difference? (hint: it’s not the color)

First, they generally live in different parts of the world. If you’re in Newfoundland or the Beaufort Sea, you can be sure you have a snow crab. Likewise, from southern Alaska to Oregon, only Tanners are around. But if you don’t know where the crab came from, the real telltale signs are in the face. Tanner crab have red eyes and pointy M-shaped mouths, while the blue-eyed snow crab has a flat mouth. And if you can’t see the face, look at the shape. The main shell (or carapace) of Tanner crab is more oval and less rounded.

Tanner crab also look much more menacing

However, there is a problem. Tanner and snow crab can hybridize. And in the Bering Sea, where their ranges overlap, they often do! Biomass surveys indicate there are over 10 million pounds of hybrids within the Bering Sea. And these hybrids aren’t sterile, like mules or ligers. They can mate, which means we aren’t just dealing with snow crab, Tanners, and hybrids. There’s just about about everything in between!

This creates some issues for fishery management. Snow and Tanner crab fisheries are managed separately. Someone with just a snow crab permit isn’t allowed to go catch Tanners, and vice-versa. But what about the hybrids? Well, if you’re the Alaska Department of Fish and Game, you just lump all hybrids with one species. Legally, Tanner crab need both an M-shaped mouth and completely red eyes. If they lack either, they’re considered a snow crab. However, not everyone agrees with this – particularly not the people catching the crab! If you’re out on deck in the cold and the dark, sorting through crab as quickly as possible, you really don’t want to spend the time carefully peering at each crab’s face. So some have proposed instead to shrug their shoulders and just say that no matter which fishery you’re in, hybrids are legal to catch.

At first, it also seems like this is a problem for our scientific understanding! After all, we all learned in high school biology that a “species” is a group that can produce fertile offspring together. So if snow and Tanner crab can do that, why are all these marine scientists treating them as separate species? Well, because it’s convenient! The concept of a “species” is just a useful way that we have of sorting and organizing the natural world. If we strictly adhered to that high school definition, we’d get some odd results. Polar bears would be considered just an odd population of grizzlies, and cows would be managed together with bison. And when talking about animals that reproduce asexually, chaos would reign!

You’ve probably heard about grolar bears, but what about the incredibly-named BEEFALO?

In other words, when we talk about “species”, we’re just trying to understand a spectrum by binning it into discrete categories. It can sure be useful, but we should recognize that it’s something we’ve constructed, rather than something cleanly and clearly defined by biology.

On a completely unrelated note, happy Pride!

DecaPod S2E6: Interview with Laura Slater

This episode was initially recorded in April 2020… and is now finally being shared with you! In this episode, I interviewed Laura Slater, a Crab Research Biologist at the Alaska Department of Fish and Game in the Division of Commercial Fisheries, and a PhD student at the University of Alaska, Fairbanks.

We discuss her work, her PhD project: understanding mating dynamics of snow crab in the Bering Sea, and SO much more!

DecaPod S2E5: Three month project plan, and what is this frilly crab tissue?

In this episode, we go over our three month plan (grant ends in March) for finishing sample processing and analyses. We also talk about some things I’ll add to my talk for the Alaska Marine Science Symposium 2020 conference, and finally Pam identifies a strange frilly crab tissue from samples she gave us!