Justin Smith asked:
If a lobster is taken out of water and can breathe, does it drown after going back into water?
Sarah - The simple answer is no.
Lobsters have evolved to live in water. They exchange gases through their gills and they will actually die if they are out of water for too long, but they will actually survive for a small amount of time.
Their close relatives, crabs, can actually survive out of water for a bit longer, although if you take a fish out of water, it will die because it will essentially suffocate. When they're in water, their gills extract oxygen from the water, but when you take them out, the surface tension of the water makes the gills collapse, so they can't function, they can't get the oxygen out of the water.
Now some fish do actually have adaptations for air breathing, like lung fish, if they live in places like rivers that periodically dry up they need to be able to deal with that.
The reason that crabs, and to a certain extent lobsters but not as much as crabs, can actually survive in air for a time, is that they hold their gills in cavities on the undersides of their bodies. They don't actually breath air. They're still using their gills, but they’ve found a way of keeping them supported and moist, which is the most important thing.
There's actually a species of crab called a coconut crab and they've evolved something called a brancheostegal lung which is a spongy tissue, like a cross between gills and lungs, which still need to be kept moistened, but they will actually exchange gas with the air.
Lobsters do also have gills in chambers, but they still require water. So they will survive in air as long as their gills are kept wet. They also have something called the gill bailer which has the best name - it’s called a scaphognathite which helps to keep water moving across the gills.
So, they will suffocate if they're on air, but they will not drown in water.
Justin Smith asked the Naked Scientists: If a lobster is taken out of water and can breathe, does it drown after going back into water? What do you think? Justin Smith, Tue, 14th Dec 2010
I don't think there would be a problem with the lobster re-entering water. The main problems these animals have is that their gills need to be immersed in water to maintain their structure, so they cannot function in air; but so long as they don't dehydrate too seriously, they should be able to re-enter the water after an episode of air exposure without compromise...but what does everyone else think?
Yes I think it is the gills, the filaments get stuck together when the lobster is out of the water and when it is put back into the water there is less surface area for oxygen to diffuse through. Chemistry4me, Thu, 16th Dec 2010
But don't the gills just re-suspend when immersed?