Hemigrapsus oregonensis

(Dana, 1851)

yellow shore crab, hairy shore crab, green shore crab, mud-flat crab, bay shore crab, Oregon shore crab

Hemigrapsus oregonensis is a small intertidal shore crab to the Pacific coast of North America. It exhibits remarkable color , ranging from deep red- to green, -green, or with various spot patterns. The is a strong osmoregulator that tolerates hypoxic and brackish conditions, allowing it to inhabit estuaries and mudflats. It is primarily , feeding on diatoms, green , and small , and serves as for shorebirds and other .

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Pronunciation

How to pronounce Hemigrapsus oregonensis: //ˌhɛmɪˈɡræpsəs ɔːrɛɡoʊˈnɛnsɪs//

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Identification

Distinguished from similar by three between the orbit and angle of the (versus two in Pachygrapsus crassipes). are smaller than Hemigrapsus nudus (3.0–3.5 cm versus larger in H. nudus). Legs covered in (hairy), unlike the smooth legs of H. nudus. Chelipeds tipped with or , lacking the purple spots characteristic of H. nudus. Carapace rectangular with no and wide-set . Color is unreliable for identification as both H. oregonensis and H. nudus commonly appear green. Males have slightly pointed , females oval; males average 34.7 mm carapace width, females 29.1 mm.

Images

Habitat

Intertidal zones under rocks, in mud flats, algal mats, eelgrass , and estuarine areas at tidal mouths of large rivers. Prefers areas with diverse matter, fine sediment, and slow, protected currents. Tolerates low salinity and turbid estuarine conditions better than most shore crabs.

Distribution

Pacific coast of North America from Resurrection Bay, Alaska to Bahía de Todos Santos, Mexico. Heavily concentrated in San Francisco Bay, coastal Oregon and Washington, and coastal British Columbia including Vancouver Island.

Seasonality

Breeding peaks in March, lowest in October. Females carry February through July; hatching occurs May through July. Rare second breeding period possible August through September.

Diet

Primarily diatoms and green ; opportunistically consumes meat and small . Functions as a scavenger and filter-feeder using maxillipeds.

Life Cycle

Females carry 100–11,000 per ovulation. Eggs undergo pre-zoeal stage while unhatched, then five post-hatching zoeal stages as planktonic . to occurs after 8–13 weeks, with timing dependent on salinity, water temperature, and food availability.

Behavior

forager that remains hidden in self-dug burrows during daylight. Rapidly burrows toward safety when uncovered. Exhibits -shuddering —rapid vibration of the chelipeds. Antennal flicking rate with body size. Initial response to simulated attack is disrupted by shipping noise (66% movement likelihood versus 32% in controls), though crabs show no evidence of developing noise based on prior exposure.

Ecological Role

for shorebirds, the ribbon Carcinonemertes epialti ( ), and the European green crab Carcinus maenas. to the parasitic isopod Portunion conformis, which can be killed by host immune response. Competes with and may impact early benthic phase Dungeness crabs in oyster shell mitigation .

Similar Taxa

Hemigrapsus nudusLarger size; smooth legs without ; purple spots on chelipeds; both commonly green despite suggesting versus purple
Pachygrapsus crassipesTransverse ridges on ; only two between orbit and angle (three in H. oregonensis)