Tuesday, August 31, 2010

A full crab is a happy crab

I love feeding my crabs, seeing them clamber for some yummy fish, and running around triumphantly with their claws in the air holding up their prize. Here, Adam and I caught some pink salmon in Echo Cove and wanted to share our catch with my boys:

video

video

Friday, August 27, 2010

It's a crab-eat-crab world

I’ll admit it: I’m an etsy junkie. I like to type in “crab” or “nautical” and just window-shop away! Check out some of these beauties that I’m dreaming about:


I can picture these on my couch!

dictionary pages are becoming a popular surface for amazing drawings, and I LOVE them!

How cute is this pin cushion???

I recently broke down and bought two prints from this seller!

While there, I stumbled upon this awesome picture by Heidesphotos:

"Crab eating crab"

It made me think about how common cannibalism is in crabs, and just how important it is for snow crabs. Opies are benthic forage feeders who mostly feed on polychaete worms, clams, and the like (I feed my guys herring mostly, and occasionally treat them with salmon and blue mussels). But their stomach contents have included small crabs, mostly found in large adult males. Because of the small amounts of crabs found, scientists don’t think these large males need the little crabs for their nutritional benefit, but their cannibalism may be an important type of population control. It’s as if they read Jonathon Swift’s A Modest Proposal and followed through on it!

Tuesday, August 24, 2010

Let's hear it for the boys

Someone once asked me why I’m studying male snow crab reproduction. My first response was, “Why not?” But the real answer is Joel Webb is monopolizing all the female crabs! No, that’s not the real answer, but it’s true. He is.

me with one of Joel's females... sigh...

The real answer is snow crab is a male-only fishery with a minimum size limit (the females aren’t targeted and, if caught, get thrown back). Removing large males can negatively affect a population because it may be giving smaller males more opportunities to mate. The idea is, because snow crabs terminally molt at different sizes, the males who are smaller than the fishery size limit will never be harvested, and therefore will be around for more reproductive seasons than the larger commercially targeted guys. If maturing smaller is a genetic trait, the smaller males’ offspring may tend towards maturing smaller too. It’s the classic case of shrinkage…

Oh, wait, that’s not what that means? Oh, well…

ANYWAY, it’s necessary to understand the role males play in reproduction, not just the females, when trying to estimate population size for management. The eastern Bering Sea stock was declared overfished by NMFS in 1999, and while the fishery continues, the stock is still in a rebuilding phase.

snow crab estimated biomass and landings showing the decline in 1999

That’s right guys, you’re important too.

Wednesday, August 18, 2010

Ask A Grad Student: Joel Webb

Want to hear about other crab lovers' work? Here you go!

Joel works as both a grad student at UAF SFOS in Juneau and as a shellfish biologist for the Alaska Department of Fish and Game. He's helped me with crab sampling in the Bering Sea and sharing his extensive literature collection, not to mention his amazing memory of past crab research.

Age: "Old"
Degree: M.S in Fisheries (pursuing the next one...)
Current City: Douglas!

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

Why aren't snow crabs taking over the world? Because most (~>99%) of them die before they can reproduce. However there may be times when the location, abundance, and number of eggs carried by mature females is related to the number of mature crab years later. By characterizing the number of eggs carried by mature females of differing size/age for several years we will estimate the number of eggs produced by the population and look for possible relationships between egg production and the abundance of small crab several years later.

Joel's trawl survey ladies ready to be measured

2. You work at sea a lot. What’s your favorite part of shipboard life? Your least favorite?

My favorite survey experience is seeing the patterns of crab size/age across the distribution; least favorite aspect of shipboard life is looking at the scale after three weeks of fried food.

Joel hard at work!

3. If you weren’t going to study crabs, what animal would it be?

The Tapertail Ribbonfish


4. After you get your PhD will you pursue a job in academia or stay with Fish and Game?

ADF&G all the way! :)

5. What is your favorite piece of crab paraphernalia?

A small tapestry acquired in Guatemala showing what could be a crab!

 
Thanks Joel!

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.

binding!

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!

Friday, August 13, 2010

Chivalry's not dead

While I’m glad I’m not a female snow crab, male snow crabs can defend females for mating, not just for munching.


video

This guy was in it to win it, even going so far as lifting the female out of the water to keep her from the other male! What a fighter!

Tuesday, August 10, 2010

A king crab tribute to Dr. Seuss

One Crab

Two Crab

Red Crab

Blue WHAAAA????
WHAT IS THAT? WHAT HAPPENED HERE??

eelpout in a blue king crab

(This poor eelpout must have wiggled his way into the blue king crab during haul back of the trawl (on the NMFS trawl survey). Both crab and fish were alive! I tried pulling the eelpout through, but couldn't, so I'm hoping they figured things out once they got back to the bottom of the Bering Sea.)

Thursday, August 5, 2010

Boys have HOW MANY and girls have WHAT?

I know we all learned a lot from Kindergarten Cop, but some things even Arnold can't teach us!

This blog is about love for snow crabs, but also about snow crab lovin', and as such I feel the need... the need for speed. NO! Sorry, I just kinda slipped into that. No, I feel the need to explain snow crab sexual structures.

First the females: their abdominal flap is wide, almost the entire width of their body when they're mature. This allows them to hold as many fertilized eggs between their abdominal flap and body as possible. Next they have two spermathecae under their abdominal flap, where males deposit spermatophores (capsules of sperm) for the females to use at their leisure when fertilizing eggs. It's said the sperm in the spermathecae are viable for up to 3 years! Storing sperm is a handy way to fertilize subsequent clutches without having to find a male and mate again, especially since mating can be so violent.

juvenile female abdominal flap

male abdomen

Why do females have two spermathecae? Because males have two gonopods (crab penises)!! Yep, it's not just for sharks; snow crab males are cool too. The gonopods are hidden under their abdominal flaps, which are quite skinnier that females' flaps.

two gonopods under the male's adbominal flap

Males will hold the females in an abdomen-to-abdomen position in order to do the deed, then guard the females afterward in case there are any other males around. Once the females extrude their eggs and fertilize them, the males know their job is done, and they go their separate ways.

Monday, August 2, 2010

Why I'm glad I'm not a female snow crab

Understanding any hormonal differences between new- and old-shell males is one thing, but getting to see a new-shell male compete with an old-shell male for a female is the icing on this project's cake! Imagine my excitement when my first female molted (and wasn't eaten by her girlfriends) and was ready to mate - females mate after they've molted to maturity and are still soft. It was 6 pm and the experiment needed to be filmed for 12 hours, so instead of just waiting to start the next morning, I did what any normal person would do: asked my husband to get the sleeping bags and some Chinese take-out, and got started!

Adam at the lab

I put my new, precious, soft-shell female into the tank with two males and some herring (you know, in case they wanted a snack...) and started taping. Things were really slow for the first 6 hours, then things got crazy!

video

The small crab is the female, playing the edible rope in a medieval tug-of-war: the old-shell male (with white barnacles attached to his back) ate 2 1/2 of her legs! Don't worry, I took her out and put her in her own little hospice area. And then I sampled the males for their gonads.

But how representative is this behavior compared to opies in the wild? Maybe more representative than you'd think. This carnage was captured in the Bering Sea by ADF&G:




And that's why I'm glad I'm human.