For crabs to do well on land instead of in water, they need to change a number of physical and morphological traits, including the ability to reproduce without being able to get to open water. Some species have changed their gills to help them exchange gases, but many species also have extra gas exchange organs, usually lungs. People who are good at breathing through their noses and mouths make their lungs bigger and more vascularized. Pulmonary vessels carry oxygenated blood to the heart. The high amount of oxygen in the air leads to low ventilation, which creates an internal hypercapnia that pushes CO(2) out of the body. Land crabs can get blood through either their lungs or their gills, and the way they switch between the two can depend on their respiratory system or how much they are exercising. During their breeding migration on Christmas Island, Gecarcoidea natalis kept their arterial Po(2) steady by uptaking O(2) through branches, but their pulmonary O(2) pressure went down. This was partly because exercise increased the flow of blood through their gills by two times. Related species depend on high levels of haemocyanin and an affinity for oxygen to help them take in nutrients, but this makes it harder for the tissues to unload and lowers their aerobic range. Water crabs use their gills to exchange salt and ammonia with water, but land crabs can’t do this. Birgus latro has adopted uricotelism but other species excrete ammonia in either the urine or as gas. Land crabs minimise urinary salt loss using a filtration-reabsorption system analogous to the kidney. Urine is redirected across the gills where salt reabsorption occurs in systems under hormonal control, although in G. natalis this is stimulatory and in B. latro inhibitory. Different species of crabs live in different types of habitats, from water to land. However, their bodies are not all the same. Each species has its own unique set of physical traits that help it survive in its own environment.
With their hard, protective shells and sideways scuttling, crabs are one of the most fascinating creatures found along coastlines worldwide But beneath that tough exterior lies some equally remarkable biology that enables crabs to thrive in their habitats, including specialized adaptations for breathing So how exactly does a crab take in that vital oxygen and expel carbon dioxide? Let’s pull back the shell and explore the intricacies of a crab’s respiratory system.
Anatomy of a Crab’s Gills
Like many aquatic animals, crabs utilize gills for respiration. Their gills are delicate structures rich in blood vessels, located under the carapace (top shell). This placement helps protect the gills from damage while also allowing water to easily flow over them.
Crabs have nine gills on each side of their bodies. The gills are composed of hair-like structures called setae which maximize surface area for gas exchange. Oxygen from the water diffuses into the bloodstream while carbon dioxide exits the body.
How Crabs Draw Water Over Their Gills
Simply having gills isn’t enough – crabs need a way to actively pull oxygen-rich water over those gills. This is accomplished using a specialized apparatus called the scaphognathite or gill bailer.
The scaphognathite is a large, plate-like structure found on the crab’s underside, near the base of the legs. By moving the scaphognathite in a paddling motion the crab creates a current that flows across the gills allowing for constant oxygen uptake.
Breathing On Land
One amazing fact about crabs is their ability to breathe out of water for extended periods As long as their gills stay moist, crabs can survive on land for over 24 hours
To prevent gill dehydration, land crabs rely on:
- Storing water in their blood, bladder and specialized pockets
- Sealing in moisture using articulating plates over the gill chamber
- Accessing external water sources like dew, rainwater, damp sand
Additionally, bubbles around a land crab’s mouth are part of an oxygen exchange process that helps keep the gills functioning.
Adaptations For Intertidal Zones
Crabs that inhabit intertidal zones have evolved adaptations to the fluctuating water levels. These include:
- Burrowing into the sand or mud during low tide
- Climbing rocks to stay immersed in tidepools
- Sealing themselves in rocky crevices
All of these behaviors allow crabs to stay moist and access the oxygen they need to survive between tides.
Examples of Crab Respiration
Now let’s look at a few specific examples of how respiration works in different crab species:
Fiddler Crabs
Fiddler crabs live in mangroves and mudflats along brackish coastlines. They utilize gills much like aquatic crabs but also have specialized cells that can absorb oxygen from air. Their burrows help retain moisture while they wait out low tides.
Coconut Crabs
The coconut crab is a terrestrial species that lives its life primarily on land. It depends completely on moisture sealed within its shell since it cannot immerse in water. Coconut crabs carry water in their abdomens and obtain external water from rain and damp substrates.
Blue Crabs
Perhaps the most widely recognized species, blue crabs thrive in estuaries and tidal marshes. Their gills must stay moist, so they hide in mud during low tide. Blue crabs can survive 24-48 hours out of water by utilizing adaptations like sealed moisture and foaming at the mouth.
Keeping Gills Moist is Key
Regardless of habitat, crabs rely on keeping their gills moist to breathe. Their specialized respiratory adaptations allow for oxygen extraction from both air and water. Next time you see a crab scuttling along the shore, take a moment to appreciate the unique biology that allows it to survive in two worlds!
Your saved search Name of saved search: Search terms:
- Yes
- No
Email:
Add to My Bibliography
- My Bibliography
Unable to load your delegates due to an error
How do Crabs Breathe In AND Out of the Water?
FAQ
How do crabs breathe air?
How long can crab stay underwater?
Which crabs have lungs?
Can crabs and lobsters breathe air?