Okay, my crotch has been itching lately…
…
Just kidding, actually I have a question about the larger and edible sea dwelling type.
I went down to this place in DC (I can’t recall the name, it had lots of fresh fish and was akin to an outdoor market) and something strange occured to me:
They had live crabs for sale. Out of the water. Still living.
Am I missing something here?
Don’t crabs have gills? How could they survive on land for that amount of time?
Yes the crabs you see in the market have gills. However all crabs can survive being out of water for some time. There are three things that kill marine life when they are taken from the water: dehydration, collapse and suffocation. Crabs have an airtight shell surrounding their bodies, so dehydration is not an immediate problem as it is for fish or soft bodied marine life. The shell also forms a very solid skeleton that prevents the body from collapsing and the internal organs from being crushed and killing the critter.
Invertebrates like crabs don’t need to use a lot of oxygen to begin with, which is why it takes forever to drown insects. They have a huge anaerobic scope compared to vertebrates. Added to this many invertebrates can go into a state of torpor when faced with oxygen starvation. In this state they use virtually no oxygen, and the state is only broken by the presence of oxygen. This ability has been further refined in many crabs by the habit of spending large parts of each day/night in anoxic burrows. Even crabs that no longer do this have recent ancestors that did. They are very good at surviving with no oxygen.
Many crabs of course are creatures of tidal flats, estuaries and the intertidal zone. These animals store water in the gill pouches and use that to extract the moisture that diffuses out of the air. These species would have no trouble surviving many days or possibly weeks out of water.
I just wanted to point out that my tanks for shore crabs have always included either a “shore” at one end or rocks and shells which protrude out of the water. The crabs often come up and spend time on the dry areas. They seem to bask in the sun, much like a reptile.
Another side note; they do very well on a diet of dried shrimp. I’ve also had them eat dried, fresh or frozen “blood” or tubafex worms, commonly sold in petstores as fish or newt food.