Why Crabs Keep Leaving the Sea for the Land | Summary and Q&A

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February 11, 2021
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Why Crabs Keep Leaving the Sea for the Land

TL;DR

Crabs have evolved multiple times to adapt to land, facing challenges such as breathing, supporting their body weight, and finding suitable food sources.

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Questions & Answers

Q: How do crabs breathe on land?

Land crabs have adapted through the use of lungs or modified gills. Lungs, such as those found in robber crabs, allow them to breathe air. They breathe in through openings near the base of their walking legs and out through their mouths. Some crabs also switch between gills and lungs as needed.

Q: What is a hydrostatic skeleton, and how does it help crabs on land?

A hydrostatic skeleton involves pressurized internal fluids that help support the crab's body on land. While all crabs have this system, land crabs require higher fluid pressure to counteract gravity. However, this can make them more prone to rupturing their new exoskeletons.

Q: How do land crabs adapt to eating in a terrestrial environment?

Land crabs primarily rely on vascular plants, fruits, and leaves as their food sources. These foods are tougher and often have hard-to-digest fibers and compounds that can be potentially toxic. Land crabs have developed adaptations such as slower growth, longer lifespan, gut enzymes to digest cellulose, and possibly a reliance on gut microbes to help digest these tough plant materials.

Q: How do land crabs reproduce on land?

Most land crabs still depend on water for their larvae. Some species, like hermit crabs, release their eggs near high cliffs, allowing the hatchlings to reach the ocean. Others solve this challenge through brooding, where they carry their young in pouches until the time is right. Some remarkable species actively care for their young and raise them away from water, creating unique environments for their offspring.

Summary & Key Takeaways

  • Crabs have transitioned from living in water to living on land through a process called terrestrialization, which has happened at least five times in crustaceans.

  • Breathing on land is one of the most significant challenges for crabs, but they have adapted through the use of lungs, modified gills, or a combination of both.

  • Supporting their body weight on land is achieved through the use of a hydrostatic skeleton, which involves pressurized internal fluids that act as a support system.

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