Crabbing in the Chesapeake

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Science  18 Apr 2008:
Vol. 320, Issue 5874, pp. 290
DOI: 10.1126/science.320.5874.290a

As the state crustacean of Maryland, the blue crab (Callinectes sapidus) is dear to the hearts and stomachs (and wallets) of many residents. The commercial crabbing season opened just a few weeks ago, and pessimistic forecasts for the size of this year's harvest have led to draft proposals that more stringent protection of adult females be implemented. Kamio et al. describe a laboratory study of the courtship behavior of the male blue crab and interpret it as an adaptation to their environment. They observed that upon being presented with an inaccessible female (corralled by plastic mesh), male crabs spread their chelae (the first pair of legs in a decapod crustacean, commonly referred to as claws in crabs and lobsters) and elevated their swimming legs (the last pair of legs) into a dorso-medial position. When in this stance, the males paddled their swimming legs circularly and 180° out of phase. Particle imaging velocimetry revealed a forward-directed flow of water traveling at an average speed of 3 cm s−1. The authors suggest that the marshy habitat of the Chesapeake Bay allows female crabs to avoid predators while signaling their presence by pheromone; the males have adopted courtship paddling as a means of wafting their own chemical lures toward unseen females in order to coax them into open water. — GJC

J. Exp. Biol. 211, 1243 (2008).

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