Grapsidae

Grapsidae is a family of crabs, commonly known as grapsid crabs or shore crabs. They are distinguished by their characteristic square-shaped carapace and laterally compressed bodies, making them well-adapted for life in intertidal zones. These crabs are found in diverse habitats worldwide, ranging from rocky shores and mangrove forests to estuaries and freshwater environments.

Grapsus intermedius

Pachygrapsus planifrons

Pachygrapsus gracilis

Pachygrapsus Minutus – Pachygrapsus minutus

Thukuhar Shore-crab, Alamihi Crab, Mangrove Crab, Mangrove Rock Crab – Metopograpsus thukuhar

Alamihi Crab – Metopograpsus messor

Sally Lightfood Crab – Grapsus adscensionis

Characteristics

Grapsid crabs exhibit several unique characteristics, including:

  • Carapace: Square-shaped, often broader than long.
  • Body: Laterally compressed, allowing for movement in narrow spaces.
  • Eyes: Prominent, often positioned on stalks.
  • Chelipeds: One pair of large claws used for defense and feeding.
  • Walking legs: Four pairs of walking legs, often flattened for clinging to surfaces.
  • Respiration: Breathe through gills, but can tolerate periods out of water.

Environments

Grapsid crabs are highly adaptable and can thrive in a variety of environments. They are commonly found in:

  • Intertidal zones: Rocky shores, mudflats, and sandy beaches.
  • Mangrove forests: Live among the roots and branches of mangrove trees.
  • Estuaries: Brackish water habitats where rivers meet the sea.
  • Freshwater: Some species have adapted to live in freshwater streams and lakes.

Diet

Grapsid crabs are omnivorous, feeding on a wide range of food sources, including:

  • Algae: Graze on various types of algae.
  • Detritus: Feed on decomposing organic matter.
  • Small invertebrates: Prey on insects, snails, and other crustaceans.
  • Carrion: Scavenge on dead animals.

Reproduction

Grapsid crabs reproduce sexually, with females laying eggs that hatch into planktonic larvae. The larvae drift in the ocean for a period before settling and undergoing metamorphosis into juvenile crabs.

Examples of Grapsid Crabs

Some well-known examples of Grapsid crabs include:

  • Sesarma reticulatum (Fiddler crab): Known for their distinctive large claw in males, used for signaling and attracting mates.
  • Uca pugnax (Atlantic fiddler crab): A species found along the Atlantic coast of North America.
  • Pachygrapsus crassipes (Shore crab): A common species found on rocky shores along the Pacific coast of North America.
  • Geograpsus crinipes (Sally Lightfoot crab): A highly agile species found on rocky shores in the Pacific Ocean.

References

Evolutionary History of the Grapsid Crab (Decapoda: Brachyura: Grapsidae)
A Revision of the Family Grapsidae Latreille 1802, with the Description of Five New Genera