Pachygrapsus crassipes
Randall, 1840
striped shore crab, lined shore crab
Pachygrapsus crassipes is a small intertidal crab to the northeastern and northwestern Pacific Ocean. It exhibits strong behavioral for life at the air-water interface, spending over half its time on land while maintaining aquatic respiration through periodic submersion. The shows pronounced activity patterns synchronized with tidal cycles. in the western Pacific (Korea and Japan) represent an isolated lineage diverged approximately 0.8–1.2 million years ago, not a recent invasion.
Pronunciation
How to pronounce Pachygrapsus crassipes: /ˌpækiˈɡræpsəs ˈkræsɪpiːz/
These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.
Identification
Distinguished from shore crabs by square (not rounded) with bold green striping on dark background. Hemigrapsus nudus (purple shore crab) has rounded carapace and lacks striping; H. oregonensis is smaller with different preferences. Pachygrapsus transversus (where ranges overlap) has more transverse carapace and different .
Images
Appearance
square, reaching 4–5 cm in width. Coloration variable: carapace typically , purple, or black with green longitudinal stripes. Chelipeds () red to purple with mottled and striped pattern on upper surface, whitish-gray on lower surface. legs purple and green with mottled appearance.
Habitat
Rocky intertidal zones and hard-mud soft seashores. Occupies crevices and shelters under rocks during daytime low tides. Tolerates extended aerial exposure, with microhabitat use varying by tidal state and risk.
Distribution
Northeastern Pacific: central Oregon to Ensenada, Baja California, Mexico; isolated at Bamfield, Vancouver Island, Canada. Northwestern Pacific: Korea and Japan (, non-). El Niño events periodically transport northward beyond usual range, establishing temporary populations >1000 km north of core distribution.
Seasonality
Year-round resident in core range. Megalopae (settlement-stage ) recruited via internal-wave transport during spring-summer settlement windows. Temporary northern established 1–4 years following strong El Niño larval influx events.
Diet
Opportunistic . Consumes green (Ulva), red algae, seaweed, diatoms; animal includes , mussels, limpets, , hermit crabs, isopods, , and (especially post- individuals). Preference hierarchy: small mussels > large mussels > seaweed.
Life Cycle
Complex with planktonic larval development. Megalopae (post-larval stage) employ diel vertical synchronized with internal-wave bores for selective tidal-stream transport and shoreward settlement. Females carry ; direct development not observed.
Behavior
Strong circadian with peak activity during high tides. Aggregates in shelters during daytime low tides. Aggressive occurs around food resources without territorial defense. -seeking rapid; escape response includes sideways . Can sustain aerial respiration up to ~70 hours through periodic wetting. Hunting strategy -dependent: more on rocky shores at night, more in intertidal pools during day. Social hierarchy forms within local .
Ecological Role
Grazer on intertidal contributing to . on small including gastropods; consumption rates on Littorina sitkana 10-fold higher than Hemigrapsus nudus with equivalent size. for seagulls, octopuses, rats, raccoons, and humans. Vulnerable to especially during stages. Lead in may reduce risk to predators consuming soft tissues.
Human Relevance
Consumed by humans in some areas. Subject of ecotoxicological research due to lead accumulation in industrialized coastal areas. Periodic northern range expansions during El Niño events create concern for impacts on . Used as for salt marsh condition assessment.
Similar Taxa
- Hemigrapsus nudus purple shore crab with rounded , lacks striping, lower on gastropods
- Hemigrapsus oregonensisSmaller shore crab with different salt marsh microhabitat preferences
- Pachygrapsus transversusOverlapping range in some areas; more transverse and different
More Details
Lead accumulation
from lead-contaminated sites carry body burdens >2300% higher than reference populations, with lead sequestered primarily in rather than soft tissues. This may explain absence of detectable behavioral impairment despite high total body burdens.
El Niño-mediated range expansion
Strong El Niño events increase winter larval abundance and poleward transport in the Davidson Current, establishing temporary breeding >1000 km north of core range. These events demonstrate climate-driven range dynamics with potential ecological impacts on temperate lacking defenses against this subtropical .
Sources and further reading
- BugGuide
- Wikipedia
- GBIF taxonomy match
- iNaturalist taxon
- NCBI Taxonomy
- Catalogue of Life
- Emily Bick: Salinity, the Water Hyacinth and a Weevil | Bug Squad
- A rare opportunity to do fall insect collecting in western North America | Beetles In The Bush
- Bee Assassin on Coneflower | Beetles In The Bush
- How to Become a Vulture: Tropical Bees and Their Gut Microbes
- Milichiideae | Beetles In The Bush
- Behavioral Ecology of the Crab, Pachygrapsus Crassipes
- Lead Burdens and Behavioral Impairments of the Lined Shore Crab Pachygrapsus crassipes
- Behavioral basis of internal-wave-induced shoreward transport of megalopae of the crab Pachygrapsus crassipes
- Observations on Life History of a Gregarine of the Striped Shore Crab, Pachygrapsus crassipes.
- Factors influencing the distribution and coexistence of Pachygrapsus crassipes and Hemigrapsus oregonensis (Decapoda: Grapsidae) in a California salt marsh
- Spatial and temporal movement of the lined shore crab Pachygrapsus crassipes in salt marshes and its utility as an indicator of habitat condition
- Getting a grip on the intertidal: flow microhabitat and substratum type determine the dislodgement of the crab Pachygrapsus crassipes (Randall) on rocky shores and in estuaries
- Periodic invasions during El Niño events by the predatory lined shore crab (Pachygrapsus crassipes): forecasted effects of its establishment on direct-developing indigenous prey species (Littorina spp.)