Green Shore Crab
Hemigrapsus oregonensis
Classification
- Phylum: Arthropoda
- Subphylum: Crustacea
- Class: Malacostraca
- Superorder: Eucarida
- Order: Decapoda
- Infraorder: Brachyura
- Family: Grapsidae
- Genus: Hemigrapsus
- Species: oregonensis
Pronunciation
How to pronounce Hemigrapsus oregonensis: //ˌhɛmɪˈɡræpsəs ɔːrɛɡoʊˈnɛnsɪs//
These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.
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Summary
Hemigrapsus oregonensis, commonly known as the green shore crab, is a small intertidal crab found along the Pacific Coast of North America known for its variable coloration and habitat preferences.
Physical Characteristics
Intertidal crab with wide-set eyes, no rostrum, and a rectangular-shaped carapace that can vary in color, typically deep red or brown with light green spots, but also grey-green, yellow-green, pale green, or white with small blue/black spots. The carapace typically measures 29.1 mm wide for females and 34.7 mm for males. Males have a slightly pointed abdomen shape, while females have an oval shape. The legs are covered in setae, and the claws are tipped with white or yellow without purple spots. The hind leg merus is unflattened.
Identification Tips
Distinguished from Pachygrapsus crassipes by the presence of three teeth between the orbit and lateral angle, as well as by its smaller size compared to Hemigrapsus nudus. Also, H. nudus lacks setae on its legs and exhibits purple spots on its chelipeds.
Habitat
Typically found under rocks in intertidal zones, mud flats, algal mats, eelgrass beds, and tidal mouths of large rivers (estuaries).
Distribution
West Coast, USA from Resurrection Bay to Bahía de Todos Santos, heavily concentrated in San Francisco Bay, Oregon, Washington, and coastal British Columbia including Vancouver Island.
Diet
Primarily consists of diatoms and green algae, but can also scavenge on small invertebrates and filter-feed using maxillepeds.
Life Cycle
From February to July, female crabs carry eggs, which hatch from May to July. A second breeding period may occur in August, hatching in September. The eggs transition to planktonic larvae in five post-hatching zoeal stages and metamorphose into adults after 8-13 weeks.
Reproduction
Breeding peaks in March; females can carry from 100 to 11,000 eggs per season, which undergo a pre-zoeal stage before developing into planktonic larvae.
Predators
Preyed upon by shorebirds, red ribbon worms, and the invasive European green crab, Carcinus maenas.
Conservation Status
Unevaluated; included in a 2009 petition for endangered species label but lacked sufficient scientific information.
Ecosystem Role
As a scavenger, it plays a role in the decomposition of organic matter and may influence the population dynamics of small invertebrates.
Similar Taxa
Misconceptions
Coloration can be variable and is not a reliable method for identification; both H. nudus and H. oregonensis can appear in shades of green.
Tags
- Crustacea
- Shore Crab
- Oregon
- Ecosystem