Monday, August 13, 2012

Lobsters vs. crabs - a crustacean showdown!

In cataloging some reprints here at the museum, I came across a guide leaflet from the American Museum of Natural History (AMNH) from 1929. It is a small leaflet entitled, "Outposts of the Sea," by Roy Miner, and it details some aspects of intertidal and shallow sea life. It also has an awesome subtitle, "The animals of the tidal realm - Marine hosts that today assail our continental borders, endeavoring to repeat the conquest attained ages ago by the ancestors of the present land-animals." How awesome is that? I am now envisioning an army of lobsters crawling onto the beach with their chelae (claws) raised in protest at our occupation of the land.
Roy Waldo Miner (curator of Marine Life at the AMNH) wrote an informative and enlightening look at the shallow seas that surround our country and the creatures who inhabit it. He touches on all of the major groups including arthropods, echinoderms, molluscs, cnidarians, and an assortment of "worms".
What initially caught my eye about this leaflet is the drawing on the cover that shows a lobster attempting to grab a crab in its claws. My first thought was that this was a cute bit of whimsy, but not knowing much about lobster and crab interactions I left it at that. There is another picture in this leaflet that shows the same type of scene: a photograph of a diorama in which a lobster is attempting to "catch" a crab.
Curiosity finally getting the better or me, I asked our resident crab expert about the paper. Much to my surprise, I learned that the American lobster (Homarus americanus) does indeed catch and eat crabs (notably Cancer borealis and C. irroratus). A recent paper published by J. M. Hanson found that half of a lobster's diet (this being a lobster with a carapace of at least 4cm) was made up of rock crabs (Cancer irroratus). While it has been suggested (see Drew, 2011) that the Cancer crabs are evolving thicker, stronger carapaces in the eternal arms race of the sea, my money is definitely on the lobster winning in the lobster-crab showdown.

Drew, D. J. 2011. "A Comparative Morphometric Analysis of Cancer borealis Stimpson, 1859 and C. irroratus Say, 1817 (Decapoda: Brachyura: Cancridae) in the Northwest Atlantic Ocean." Bulletin of the Peabody Museum of Natural History, vol. 52, no. 2, p.241-254. full access

Hanson, J. M. 2009. "Predator-prey interactions of American lobster (Homarus americanus) in the southern Gulf of St. Lawrence, Canada." New Zealand Journal of Marine and Freshwater Research, vol. 43, no. 1, p.69-88.