Krill Kill

One of the awesome things about my job is getting to interact with scientists who are working all over Alaska. Barrow is hosting some scientists right now, and they've been kind enough to share some photos taken in July.

nothing says summer like sea ice on the beach!

The researchers witnessed a neat feeding frenzy near Plover Point involving that most ubitquitous of crustaceans: krill!

 check out those chromatophores!

You may remember seeing krill in this post from Antarctica and in this post from the Gulf of Alaska. They are EVERYWHERE! And just about every marine animal seems to benefit from them in one way or another.

krill-filled water

What made this frenzy special was these krill were washing up dead on shore, so the birds were scooping 'em up right by the beach.

"nom nom nom" - Sabine's gull

Why were they washing up dead? Were they poisoned? Was the water hypoxic? No! Let's not sensationalize this, OK people? Since the ice had retreated from this area and the wind was just right, fresh water may have been pushed out from Elson Lagoon around Plover Point and shocked the little marine critters. The birds just happened to be in the right place at the right time to take advantage of it!

Plover Point is right on the edge where Elson Lagoon and the Beaufort Sea meet

"I'll take my krill on the rocks, please."

The scientists just happened to be there too for some beach seine surveys. Hooray for great timing!

a beach seine topped by krill as they are washed ashore

Cod are just like people:

They love to eat snow crabs!

You may remember meeting Laurinda Marcello through an interview last year as a student, but she's since graduated and published her results! Her paper looked at how snow crab recruitment is affected by water temperature and cold area extent, spawning stock biomass (how many crabs are out there makin' babies), and the biomass of crab predators (cod!). As a bonus, she compared these relationships between the Bering Sea and the Canadian North Atlantic.

What did she find out? Let's start with the predators! We know that cod like to eat snow crabs. I've had a cod puke little baby snow crabs on me (it had been through a lot, the poor cod, so I wasn't mad or anything). And check out this piece of knowledge:

snow crabs (in the orange square) make up a relatively large percentage

of both frequency of occurence (%FO, on the top half of the figure)

and stomach content weight (%W, on the bottom half) compared to

red king crabs and Tanner crabs in Pacific cod stomachs (from this paper)

Interestingly enough, Laurinda's study only saw an inverse relationship between predator abundance and snow crab recruitment in one study area! The rest of the areas had no real pattern. This could suggest that, while cod eat snow crab, there may not be enough predation on their part to be considered a top-down effect on snow crab recruitment. (That's a big statement up in here!) However, she warned us not to be too hasty with this conclusion as predator biomass may not mean direct predation pressure on the crabs.

Moving on, spawning stock biomass in both the Bering Sea and one portion of the North Atlantic study area was inversely related to recruitment. What? More baby-makers mean less babies? Crazy town sea, right? Laurinda posited that since snow crab reproduction relies on not only males and females to be present, but for them to be within each other's vicinity, simply looking at the number of adults may not accurately represent the number of mating adults. There's also the case of cannibalism in snow crabs: more adults mean more cannibalistic mouths to feed!

"Get into my belly!" - large snow crab

The big result was that the main factor associated with snow crab recruitment was the ocean climate. From her paper, "[t]his strongly supports our hypothesis... that cold conditions during early life history stages promote subsequent snow crab recruitment."

the colder the temperature (to a point), the more recruits to the fishery!

Cool! (Get it? wink.) Congratulations on the paper, Laurinda!

Read the full paper:
Marcello, L. A., F. J. Mueter, E. G. Dawe, and M. Moriyasu. 2012. Effects of temperature and gadid predation on snow crab recruitment: comparisons between the Bering Sea and Atlantic Canada. Marine Ecology Progress Series 469: 249 - 261. doi: 10.3354/meps09766

Mysteries of the (Long Island) Deep

My friend and fellow Southampton College alum, John Carrol, found this dead, partially eaten snail during one of his dives off Long Island:

What happened here?? He answers the mystery at his blog, Chronicles of Zostera, but I’ll give you a hint: it may have something to do with an arms race of sorts (read more about that here, here, or here).

Time it took for four crab species to break into and eat Littorina sitkana snails, grouped by snail size. The numbers above each bar represent prey biomass (mg) over total handling time (minutes) - this measure represents "prey profitability", like how much bang the crabs got for their buck. Crab claw morphology is pictured below each species name. Scale bar is 10 mm.

Adapted from Yamada and Boulding (1998)

Misleading Mammal

Well, they fooled me. There’s a seal named Lobodon carcinophaga, which means “lobe-toothed crab eater”: the crabeater seal.

possible culprit of crab predation, or is it???

But you know what, these seals DON’T eat crabs. Crabs aren’t even on their radar (these seals live in Antarctica, where crabs do not roam). They eat krill with their specialized teeth.

crabeater seal skull on display at the Crary Labs Museum in Antarctica

tastey krill

And their teeth must be pretty special, because they eat 80 million tons of krill a year! Then leopard seals eat them.

AHHHHHHHH!

So now I know, and knowing is half the battle.

Note: there aren't polar bears in Antarctica either. Just so you know.