We received several correct guesses. This is the zoea (free-swimming larval stage) of a Pelagic Red Crab (Pleuroncodes planipes)! The photo below shows the entire zoea:
We haven't been able to find many pictures of Pelagic Red Crab larvae, so we thought it would be fun to share a few. Eric also recorded some video (see below)!
Here's the basic sequence of events:
After finding live Pelagic Red Crabs on 24 January 2017, I was measuring them and counting the number of males and females. I discovered that several of the females were carrying eggs. Similar to lobsters, they brood their eggs attached to the underside of the abdomen (see below):
We wondered if the embryos would develop in Northern California waters. Based on a previous study that found they did well at 12°C, it seemed like they should develop and hatch in ~22 days.
Right on schedule, the embryos hatched today (after a minimum of 22 days)! This is what we saw when we came into the lab this morning — an adult female surrounded by hundreds of larvae, each ~2 mm long:
And here's a close-up of some of the larvae in the jar:
Carl Boyd described the larval stages of Pelagic Red Crabs in 1960. This drawing shows the first zoea:
Modified from Boyd, C.M. 1960. The larval stages of Pleuroncodes planipes Stimpson (Crustacea, Decapoda, Galatheidae). Biological Bulletin 118: 17-30.
And here's a close-up of a zoea in a similar position (shown in dorsal view, from above):
As mentioned, Eric took advantage of a rare opportunity to film some live Pelagic Red Crab larvae. You'll see the very active newly-hatched zoeae zipping around. (Among the swimming sequences and close-ups, watch for the rapidly beating heart.) Note: If you receive this via e-mail and can't see the video file below, click on the title of the post above to go directly to the web site.
I can't help showing a couple more pictures — two extreme close-ups. Check out the beautiful telson (last abdominal segment or "tail")...
...and the wonderful second antenna (the outermost antenna, adjacent to the eye):
We feel very fortunate to have observed and photographed these fascinating larvae. We hope you enjoy them, too!
Beautiful photos and videos. Love the detail.
ReplyDeleteToday (November 14, 2018), in Pacific Grove, CA, at Lover's Point, the pelagic red crabs arrived, this after a nearly 3 degree temperature increase the previous day (Station 46240 - Cabrillo Point, Monterey Bay, CA). I swam approximately .5 miles in very clear water and observed numerous adult crabs swimming up to approximately the 1-2 meters water depth. I'm guessing this depth may be a natural defense that keeps the crabs from becoming food for the swarms of waiting western gulls who cannot dive that deep for food. I saw no evidence of zoeas or egg clutches under several of the beached crabs that I examined. There were mass strandings along the recent high tide line. Had great fun examining one of these crabs with a 60x field magnifier; incredible body features! The ocean really delivered today!
Chuck
lerable@sbcglobal.net
Hi, Chuck!
ReplyDeleteThanks so much for sharing your observations! It's interesting that the Pelagic Red Crabs are showing up in Monterey at this time. Although there's an 80% chance of a minor El Nino this winter, it's unusual to find the red crabs so far north without active, significant El Nino conditions. It's a bit of puzzle! Perhaps there were some red crabs that were somehow left behind after last year's northward movements? Or, maybe the poleward-flowing currents have been unusual this summer/fall? We'll keep our eyes open in Bodega Bay.
Jackie