Showing posts with label molting. Show all posts
Showing posts with label molting. Show all posts

Friday, May 18, 2012

How does Ophilia grow?

Ophilia the opilio is back with another mini-book! This time you and your friends/kiddos/pets can learn how a crab grows: through the molting process.

It's a very simplified version of what goes down for our little crustacean friends, but you can learn more about the hormones involved here, the terminal (or final) molt in snow crabs here, growth through a succession of red king crab molts here, and watch a video of a spider crab molting below (it's pretty crazy!).

To make your new mini-book:

1. Just download this pdf and print it out.

2. Follow the instructions from the original Ophilia post.


3. Learn (or teach), color, and enjoy!

this guy worked really hard, but it paid off in just how big he was able to get!

Tuesday, February 1, 2011

They grow up so fast… when they’re cold

Here's the paper I wanted to share with you but then got distracted on Australia Day:

You’d think that, given their name, snow crabs would like the cold. And they do: 97.8% were associated with eastern Bering Sea bottom temperatures between -2.0 and 4.0° C (Otto, 1998). Once they get to 7° C, their metabolism starts kicking in too much and they expend more than they can consume (their energy budget goes in the red; see Foyle et al., 1989).

That being said, a new paper came out showing opies terminally molt at younger instars when in colder temperatures. AnnDorte Burmeister and Bernard Sainte-Marie (a rock star in the snow crab world) recently looked at the geographic variation in size at terminal molt of snow crabs off the west coast of Greenland. They found that in both male and female snow crabs, size at terminal molt is positively correlated with temperature. They explained this by snow crabs possibly terminally molting at lower instar numbers (maturing faster) rather than growing less during each molt. Growing the same amount in different temperatures kinda rocked my socks, but Burmeister and Sainte-Marie did see similar sizes at instars between two sampled bays despite temperature differences!

carapace widths of terminally-molted male and female snow crabs
along western Greenland: larger adults are found at higher temperatures
(this pattern is also seen in eastern Bering Sea females = black diamonds)

While this study did not see a relationship between size and latitude, the idea of decreasing size with decreasing temperature can be related to latitude through the ‘converse Jame’s cline’. The Bergmann/Jame’s clines describe a positive relationship between maximum size of animals and latitude. In sandy beach isopods Excirolana hirsuticauda, larger growth was observed at the southernmost study site:

isopod growth in two Chilean locations
(read more here)

The converse Jame’s cline is therefore seen in the eastern Bering Sea, where mature female snow crabs are smaller the farther north you go (I’ve seen this myself, but you can also check out Zheng et al., 2001).

Burmeister and Sainte-Marie concluded their study with implications for the fishery: seeing the relationship between temperature and terminal molt, increasing ocean temperatures can directly affect snow crab stocks by increasing size at maturity. For females, this increase will mean greater fecundity due to ability to hold more eggs in their clutches. But for males, it will mean more will be vulnerable to fishing pressure because more will molt into the fishery rather than terminally molt at sub-legal sizes.

crabbing in Disko Bay, Greenland

Read it:
Burmeister, A., and B. Sainte-Marie. 2010. Pattern and causes of a temperature-dependent gradient of size at terminal moult in snow crab (Chionoecetes opilio) along West Greenland. Polar Biology 33: 775-788.

Friday, September 3, 2010

Ask A Grad Student: Miranda Westphal

Miranda is my crab lab mate -- she's co-advised by Dr. Sherry Tamone (my advisor) and Dr. Ginny Eckert (my committee member) -- and my office mate in the Lena building, as well as my ELISA accomplice!

Age: 34

Degree: Candidate for Master’s of Science, Fisheries

Current City: Juneau, Alaska

1. Describe your project, in 4 sentences or less.

I study the growth physiology of red king crab (Paralithodes camtschaticus), specifically comparing wild caught red king crab (from Southeast Alaska) and hatchery-raised red king crab (from the Alutiiq Pride Shellfish Hatchery in Seward, Alaska). There are two aspects to my project: 1. is to determine how often the crabs molt (molt interval) and how much they grow with each molt (growth increment) 2. look at the fluctuations in circulating growth ecdysteroids (20-hydroxyecdysone) in the hemolymph throughout the molt cycle. Additionally, I conduct monthly beach surveys (during the low low monthly tides in Auke Bay) to measure the wild juvenile red king crab that live in the intertidal in order to help determine if there are any differences in growth that may result from rearing crabs in a laboratory over time. By understanding the early life history of king crabs, specifically how they grow and behave during their most vulnerable time (first few years of life), managers will be empowered to manage the fishery in a more informed and predictive manner; moreover, this research may be used to better classify (or “age”) young crabs that are encountered during surveys or other field research opportunities, giving managers and researchers a deeper understanding of how movement and behavior of differing age classes of juvenile king crabs in the field will ultimately affect the fishery into the future. (I know that last sentence is kind of long and a run-on but I only had four sentences!)

a red king crab's growth over subsequent molts (all photos scaled the same)

2. You were living in Florida before. What drew you to Alaska?

I loved working in the warm waters off of Florida but couldn't pass up the opportunity to work on an amazing crab fishery in the last frontier. It really was the project and my advisors that drew me to Alaska. The bonus is that Southeast Alaska is an amazing place to live and work!

at work on ADF&G's R/V Medeia with a blue king crab

3. What has been the most challenging aspect of your project? The most fun?

The most challenging part has been learning time management. It's a real challenge to fit in all of your research as well as classes, meetings, lab work and all of the other little things that tend to come up! The most fun is, without a doubt, working with live animals. Even though it can be challenging and time consuming, it brings me a lot of joy watching their behavior and watching them grow. I often feel more like I have thousands of little pets rather than research animals!

first stage juvenile red king crab

4. Will you continue to work with crabs after you graduate?

I sure hope so! I love working with juvenile shellfish and I really do prefer working with decapod crustaceans (e.g. crabs, shrimp, lobster, etc.). I am considering continuing on with my education and pursuing a PhD but I haven't made any decisions yet.

5. What is your favorite piece of crab paraphernalia?

When working with a specific organism or class of organisms, you really do tend to accumulate a lot of paraphernalia! Without a doubt, my favorite is my crab beach ball that I got for my birthday from my sister-in-law. I also really love the crab business card holder that I got for Christmas.

the greatest beach ball EVER!

a card holder with crabby bling

Thanks Miranda!

Monday, August 16, 2010

ELISA: not just a pretty name

We’ve talked about methyl farnesoate, the reproductive hormone, but what about the hormone that makes crustaceans molt? Ecdysteroids!

from Kumar et al., 2004

These bad boys stimulate the production of a new cuticle, or soft shell, under the old hard one, as well as stimulate the production of enzymes to separate the new and old shells.

production of a new cuticle before and after the molting process
(Thanks to Miranda Westphal for the artistic idea!)

You can tell when a crab is getting ready to molt because the ecdysteroids increase significantly:

ecdysteroid profile for Dungeness crabs

How do we measure ecdysteroids? With a competitive enzyme-linked immunosorbant assay (ELISA), of course! An ELISA works by taking advantage of the specific nature of antibodies. Rabbits are injected with crab hemolymph (blood) to make a primary rabbit antibody (1° Ab), and then goats are injected with rabbit blood to make a secondary goat anti-rabbit antibody (2° Ab). This way the 1° Ab will only bind to the 2° Ab, and ecdysteroids from crab hemolymph will only bind to the 1° Ab.

The competition comes in with the crustacean ecdysteroids: the ecdysteroids will bind to the rabbit antibodies, but in order to measure how many ecdysteroids are in the hemolymph we add marked ecdysteroids to the mix.

ELISAs are run in tiny wells. Within the wells, the 2° Ab first binds to the well wall. Next we put both the crab hemolymph and the marked ecdysteroids (“horseradish peroxidase-conjugated ecdysone”) into the wells. They can’t bind to anything yet, but we finally add the 1° Ab. This is when things go nuts! The 1° Ab is busy binding to the 2° Ab, while the two types of ecdysteroids are competing for spots on the 1° Ab. After we let the wells sit for a bit, anything that hasn’t bound to an antibody gets dumped.


The horseradish peroxidase-conjugated ecdysone turns blue during the development process. When you see a well with bright blue, it means that sample of hemolymph did not have a lot of ecdysteroids in it, which allowed for more of our marked ecdysteroids to bind to the rabbit antibodies.

an ELISA plate after development

Wells that appear mostly clear represent crabs that had a lot of ecdysteroids in their hemolymph. These crabs are the ones that are ready to molt!

Wednesday, July 21, 2010

Size Matters

One way to group male snow crabs is to use their relative claw size. Male opies can be small-clawed adolescents or large-clawed adults. Their claw size distinction is based on the height of their claw, or chela, compared to the carapace width.

It seems pretty straight forward, but the difference in claw size represents where each male snow crab is in his life cycle. Crustaceans molt/shed their hard exoskeleton in order to grow. Once they shimmy out of their old exoskeleton, they're really soft and vulnerable. But because they're soft, they're able to swell their bodies by taking in lots of water so that once their new shell hardens they're larger.

Snow crabs have a final, or terminal, molt. This means that after the terminal molt, they will no longer grow. When the males terminally molt, their claws become disproportionately larger compared to their bodies' growth. Why the larger claws? It's thought that larger claws (and larger muscles within them) give terminally-molted males a physical advantage when competing for females.

Not all male snow crabs terminally molt at the same time; some may skip a molt for a year or "choose" to stay adolescent for one more molt (it's not really well understood). Because of this, adult males come in a wide range of carapace widths. In order to determine which males are adolescent versus adult, I have to use a logarithmic discriminate function, which I won't get into too much, but I think it sounds impressive. It goes something like this: