Yellow Shore Crab
Hemigrapsus oregonensis
Summary 2
Hemigrapsus oregonensis is a small shore crab of the family Varunidae; it was formerly classified under the family Grapsidae. It is known under several common names, including yellow shore crab, hairy shore crab, green shore crab, mud-flat crab, and Oregon shore crab.
Biology 3
Biology/Natural History: This species is a better osmoregulator than the other local shore crabs (H. nudus), which is probably associated with its being more common in estuaries. It also often digs burrows and is capable of withstanding more hypoxic conditions than the other shore crabs are. Feeds mainly at night, mostly on diatoms and green algae, but will eat meat if it has opportunity. Predators include shorebirds. May have the parasitic isopod Portunion conformis in the perivisceral cavity (not evident unless dissected).
Description 4
This grapsid crab (rectangular carapace, wide-set eyes and no teeth on the carapace between, no rostrum) is a common intertidal crab. The merus of legs 2-5 is not flattened. The dorsal surface of the carapace does not have transverse ridges or lines, and is variously colored, often with light greenish spots on a dark reddish-brown background, but may be a pale green (photo), yellow-green, gray-green, or even nearly white (photo). There are 3 teeth on the anterolateral margin of the carapace (photo). The legs have abundant setae (photo)(photo), and the chelipeds have no purple spots (photo), but have yellow or white on the tips. Carapace width to 34.7 mm in males and 29.1 mm in females.
Habitat 5
Depth Range: (mainly intertidal)
Habitat: Open mud flats, algal mats and eelgrass beds, in bays and estuaries and on open beaches where there is plenty of fine sediment.
Lookalikes 6
Along the Pacific coast of North America, there are just two Hemigrapsus species (Batie 1982). The Bay Shore Crab (Hemigrapsus oregonensis) is dull brownish green, with hairy legs and chelipeds (pincers) that lack red spots. The Purple Shore Crab (Hemigrapsus nudus) is red, purple, or whitish, with no hair on the legs, and red-spotted chelipeds; a green morph of H. nudus without spots is fairly common in the northern part of its range. The Purple Shore Crab is typically found in rocky outer coast areas with well-aerated, silt-free water; in contrast, the Bay Shore Crab is more common in regions with a higher silt load and, in general, is more typical of a muddy substratum (Batie 1982 and references therein). Both of these Hemigrapsus species have a smooth carapace with three teeth on the anterolateral (sides of front) margin and no transverse lines; in contrast, another somewhat similar crab in the range of these two crabs, the Lined Shore Crab (Pachygrapsus crassipes), has a carapace with transverse flat ridges (strongest laterally), two teeth on the anterolateral margin, and a surface that is blackish green with numerous red or purple transverse lines. (Carlton 2007)
The Purple Shore Crab (Hemigrapsus nudus) has a typically reddish or brownish carapace about 3 cm wide (typically greenish in H. oregonensis), smooth legs (hairy in H. oregonensis), and red spots on the claws (H. oregonensis claws lack red spots); H. nudus is found in the lower rocky intertidal zone, in pools and rock rubble areas (H. oregonensis is restricted to bays and other more protected waters). The Lined Shore Crab (Pachygrapsus crassipes) also has a greenish carapace about 3 cm wide, but the carapace has distinct reddish transverse lines; it is found in the rocky mid and upper intertidal zone. (Brusca and Brusca 1978; Headstrom 1979)
Sources and Credits
- (c) Alison Young, some rights reserved (CC BY-NC-SA), http://farm6.static.flickr.com/5239/7184560723_d21c8cd3ac_b.jpg
- Adapted by Marisa Rafter from a work by (c) Wikipedia, some rights reserved (CC BY-SA), http://en.wikipedia.org/wiki/Hemigrapsus_oregonensis
- (c) Rosario Beach Marine Laboratory, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/10457185
- (c) Rosario Beach Marine Laboratory, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/10457183
- (c) Rosario Beach Marine Laboratory, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/10457186
- (c) Shapiro, Leo, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/17763543
