How Do Crabs Breathe? (Underwater & On Land)

The amphibious crab has a remarkable way of obtaining oxygen in both their aquatic and land habitats. While on land you may see bubbles or foam coming out of the crab’s mouth which is actually the crab taking in water, or moisture, to breathe through its gills. 

All species of crabs have a form of bronchial chambers and storage capacity that keep their gills moist when they come up onto land. Unlike many animals, crabs can reconcile between breathing on land and in the water thanks to their morphological structures aiding found in different species physiologically. 

A fascinating piece of nature to observe, it is quite remarkable how these creatures can make this special transition from the watery depths to the dry shores without any struggle.

Continue reading to discover how they actually achieve this.

Crab Gills

Crabs are amazing creatures that belong to the crustacean family, along with lobsters, shrimp and similar animals. Over 4500 species of crabs have been documented; most live in and around water bodies, but others prefer land. Although occupying different habitats, all crabs share similar morphological characteristics – a carapace on the head and thorax covers and protect their gills which helps them breathe both on land and in the water. Additionally, crab’s jointed limbs are well-equipped for two types of environments, allowing them to navigate both land and water. 

Another, fascinating ability of crabs which makes them thrive in terrestrial and aquatic environments is due to their unique respiratory system. The crucial organ for oxygen absorption is the branchial chamber where gills are housed. This can vary slightly amongst species, with some having more gills than others. Land crabs have evolved with a more elaborate vasculature containing an effective double portal system, indicating some stay on land for extended time periods, still able to breathe successfully. How do these creatures absorb the oxygen they need? Generally speaking, this occurs by osmosis moving through the semipermeable membrane of the gills. Once oxygen enters capillary blood vessels it is circulated throughout their bodies then carbon dioxide exits as waste gas. 

Habitat Specifics

Crabs, unlike other marine species, don’t take up residence at the bottom of the ocean or in vast coastal waters. Instead, they typically inhabit intertidal zones, which are shores and shoreline areas that have water levels changing with the tides. This means that crabs will often be scrambling around out of the water for hours a day. Some crab species can’t spend long periods of time fully submerged in water because they are not able to get enough oxygen from their gills as they would be able to on land; if forced underwater too long these crabs can drown. 

Interestingly, crabs don’t actually need to be completely submerged in order to draw oxygen for respiration. Instead, they rely on being kept constantly moist; thanks to their specialized gills which, depending on species and environment, can take advantage of dew, moisture from foliage and pools of water left behind by receding tides. All of this allows most crab species to easily switch between land and underwater lifestyles without expending too much energy.

Breathing Underwater

Underwater, crabs survive by using a leaflike appendage called a scaphognathite to draw water over their gills and into the gill cavity. This allows oxygen to pass into the crab’s bloodstream while also releasing carbon dioxide near its mouth. This is incredibly important as it keeps the crab alive, allowing it to search for food while also avoiding predators in their aquatic environments. Most species of crabs regularly use this method of respiration and without it, they would be unable to remain in the watery depths.

Breathing On Land

In order to cope with the dry land environment, land crabs have developed unique characteristics. A key adaptation is the use of articulated plates that seal in moisture over their gills. By storing water inside their gill chamber and other parts of their bodies such as the bladder and pockets near the tail, they can survive by reusing some of their own bodily fluids to keep their gills moist. Additionally, land crabs look for hydration sources such as dewdrops, damp hiding places, and tidepools. When a crab needs to exchange oxygen while on land it’ll often be seen bubbling or foaming at the mouth which is an indication of air being forced across moist gills and carbon dioxide being released.

Crabs are seen blowing bubbles in this video.

FAQs

Do crabs have lungs?

Crabs certainly appear to have lungs, with their two large body chambers and paired gills on either side. However, the truth is that crabs do not actually have any respiratory organs to speak of — rather, they respire using a process known as ‘gill ventilation’. 

Do crabs breathe above and below water?

The answer is that yes, crabs do possess the necessary breathing skills to survive oxygen both from water as well as from the air, allowing them to stay submerged for long periods of time.

How can crabs survive outside of water?

This is made possible by their two sets of gills, one set interior and the other exterior. Special gill chambers filled with saltwater that coat the crab’s outer surface provide moisture which allows them to breathe oxygen from the atmosphere through the external set of gills while they are out of water. 

How do crabs and lobsters breathe?

Crabs and lobsters are equipped with a unique type of respiratory system which is known as “Book gills”. These book gills are arranged in groupings, or lamellae, that are connected to the creature’s external body by tiny openings.

Do crabs breathe with lungs or gills?

While we rely on lungs to breathe, crabs and other crustaceans have quite a different system; they rely on gills to take in oxygen and excrete carbon dioxide from their bodies. Unlike humans who bring air into our bodies, the gills of a crab will pull oxygen out of the water so the crab can live and thrive beneath the waves.

Final Words

In water, these creatures use their gills to process oxygen present in the water but on land, crabs have options to get the oxygen they need. Some species have plates that cover their gills which help store moisture internally. Others can access moisture from dew, other damp places or even a reduction in the structure of their own gills by doing so. Making it suiting for different environments and terrains. Furthermore, some species also display psychological adaptations as means of survival like a branchial or lung-like chamber which is tailored to the specific environment they reside in allowing them such versatility.

Reference:

https://pubmed.ncbi.nlm.nih.gov/11923073/#:~:text=Land%20crabs%20have%20a%20dual,respiratory%20media%20or%20exercise%20state.

https://www.thoughtco.com/how-do-crabs-breathe-2291887#:~:text=Crabs%20breathe%20underwater%20by%20drawing,gills%2C%20which%20extract%20the%20oxygen.