Hemigrapsus oregonensis is a small shore crab of the family Varunidae; 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, bay shore crab and Oregon shore crab. Despite its common name, the crab actually has a wide variety of coloration. It is found along the West Coast of the United States and Canada, specifically along shorelines and similar geographical areas. In 2009, H. oregonensis was included on a list of animals petitioning for the endangered species label, but there was not enough scientific information available for it to be considered as such, so it remains unevaluated to the present day.
Description
This crab is an intertidal crab with wide-set eyes and no rostrum. Despite its name, body color can vary. Often, the crab's rectangular-shaped carapace is deep red or brown with light green spots, but it can also be grey-green, yellow-green, pale green or white with small blue/black spots, as well as have lighter colored legs with similar spots. The carapace in the hind region is free from transverse ridges, but contains three teeth between the orbit and lateral angle. The carapace typically measures 29.1 mm wide for female crabs and 34.7 mm wide for male crabs. Males and females can also be distinguished by the shape of their abdomens; females have more of an oval shape while males have a slightly pointed shape. The legs are covered in setae, and the legs with claws (chelipeds) are tipped with white or yellow with no purple spots. The merus on the hind legs are unflattened.
Habitat, distribution, and diet The entire genus is restricted to the Pacific Ocean, except for Hemigrapsus affinis which lives along the Atlantic coasts of South America, from Cape San Roque (Rio Grande do Norte state, Brazil) to the Gulf of San Matías (Patagonia, Argentina), and population of Hemigrapsus sanguineus which have been introduced from the species' native range in East Asia to the Atlantic coast of the United States from Portland, Maine to North Carolina, and to the English Channel and North Sea. This species typically lives under rocks in intertidal zones, but can also be found along shorelines, and in mud flats, algal mats, eelgrass beds and the tidal mouths of large rivers (estuaries). It prefers areas with diverse plant matter, fine sediment and slow, protected currents. Its geographical range in the United States spans from Resurrection Bay to Bahía de Todos Santos. It is heavily concentrated in the San Francisco Bay, along the coasts of Oregon and Washington, and along the west coast of Canada, specifically in coastal British Columbia and on Vancouver Island. Hemigrapsus oregonensis's diet primarily consists of diatoms and green algae, but it will occasionally eat meat, if accessible. It is a scavenger, and it will prey on small invertebrates or use its maxillepeds to filter-feed. It is preyed on by shorebirds, a red ribbon worm which targets its eggs, and the European green crab, Carcinus maenas, a non-indigenous littoral crab which has been classified as one of the world's worst invasive species.
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