Tuesday, April 24, 2012

Aging crabs

Last week was an exciting one with three defenses in three days! Congrats to my fellow successful defenders (theirs were doctoral dissertations! yikes!):

Ben Daly and Kray Van Kirk

Sherry and me before my presentation with our mugs

amazingly delicious cupcakes made by Gretchen Geiger
(the eyes are green just like snow crabs!)

During my presentation, I explained that I use the visual condition of snow crab shells as a rough estimation of how long it has been since they molted (see Step 1 here). The darker and more marked up a crab may be, the longer it has been since molting. While determining a crab's shell condition is not an exact science, shell condition index is the only way to get an estimation of age in these crusty guys.


That's right, there may be a way to age crabs after all! You see, we can use the bones of fish and mammals to get their ages since they often will lay down annual markers (much like trees). But because crabs molt, they lose that hard part that may otherwise have retained signs of growth and aging over time. And because snow crabs terminally molt over a wide range of carapace widths, size frequency distributions don't work well in estimating age groups. However, researchers think that they can measure lipofuscin, a waste material retained within the brains of crabs, in order to age them!

if he only had a brain!

Lipofuscin granules can't be degraded or exocytosed (removed from the cell), so they accumulate over time. Scientists have gotten age estimates in crayfishAmerican lobsters, and blue crabs using lipofuscin as an age index. What about snow crabs? Allain et al. (2011) measured lipofuscin from the olfactory lobe cell mass in new- and old-shell immature and mature snow crabs.

snow crab brain! (watch out for zombie crabs!)

The scientists found higher levels of lipofuscin in old-shell crabs compared to new-shell crabs, indicating the aging process! Unfortunately, snow crabs retain very low levels of lipofuscin compared to other crustaceans, and their immature animals had unmeasurably low levels, making a lipofuscin index for opies difficult to calculate. These lower levels may be due to snow crabs' cold water environment, as temperature has an effect on lipofuscin accumulation rates.

arctic sea ice extent (with the Bering Sea in the red star)=

Overall: use of lipofuscin is NOT useful for aging snow crabs, which may be bad (or just sad) news for us, but good news for those lady snow crabs who don't want to divulge their age. So don't worry, female opies, you can celebrate your "9th" birthday as many times as you want - we won't call you out on it!

Read up on aging:
Allain, R. N., M. Moriyasu, B. D. Crawford, and S. C. Courtenay. 2011. Lipofuscin quantification as a potential tool for age estimation in snow crabs,Chionoecetes opilio (O. Fabricius, 1788) (Decapoda, Oregoniidae). Crustaceana 84: 1441-1463.

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