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Explanation: Although
common, this crustacean of the coast is still a delight to observe.
Among its several common names, the most catching is "Sally
Lightfoot," which may derive from their apparent ability to skim over
the water surface as they dash among the intertidal rocks.
In the main video of this week's episode, watch as
Sally Lightfoots selectively pick algae from the pockets
of the volcanic rocks that comprise the coastlines of
the Galapagos Islands.
Sally
Lightfoots begin life mostly black with white spots ... then the black
fades into dark red (right) in the later juvenile stage as it molts ...
eventually becoming the bright red and yellow that is so eye-catching (below).
Adult stage.
An algae feast in the intertidal zone.
However, at least one study (Freire et al. 2011) discovered
that populations of Sally Lightfoot Crabs on islands of the
equatorial Atlantic Ocean became cannibalistic under
conditions of small habitat size. high local population density,
limited diversity of food items, and absence of predators.
Information:
Freire, A.S., M.A.A. Pinheiro, H. Karam-Silva, and
M.M. Teschima. 2011. Biology of Grapsus grapsus
(Linnaeus, 1758) (Brachyura, Grapsidae) in the Saint Peter and Saint Paul
Archipelago, Equatorial Atlantic Ocean. Helgoland Marine Research
65(3):263-273.
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