What happens to dead crabs' shells?

[Aspiring Writer]

Hi, I'm back. So what exactly happens to crab's shell once they die? Like, if you have seen an octopus eat a crab, you know it leaves the shell there. What happens to it? Does a certain animal break it down it some do for poop?

[Condensation she/her]

I'm almost... afraid to ask.

Well, I looked it up and found a whole lot about... humans digesting crab shells... but that's not what you want. I also found this interesting scholarly article that says that the Pacific Ocean is dissolving shells. So I'd say that they probably stay on the bottom of the ocean until they're weathered away.

[Aspiring Writer]

It's just for the ecosystem of something I'm writing that is predominantly Giant Octopuses and Craps and no fish which is difficult as I need to see how much that affects.

[Condensation she/her]

8 hours ago, Aspiring Writer said:

It's just for the ecosystem of something I'm writing that is predominantly Giant Octopuses and Craps and no fish which is difficult as I need to see how much that affects.

Ah. Well, the fish would not eat the shells, as far as I know. So it shouldn't be too much.

*decides not to correct your misspelling*

[Guest Somebody from Scadrial]

14 hours ago, Aspiring Writer said:

It's just for the ecosystem of something I'm writing that is predominantly Giant Octopuses and Craps and no fish which is difficult as I need to see how much that affects.

Actually. Some octopuses eat shells I believe, so that might help. They probably do mostly just decompose. The should totally be an animal that use shells it finds on the sea floor as armour. Likely an octopus that has a lot of control over the size of it's body.

 

[Aspiring Writer]

1 minute ago, Somebody from Sel said:

Actually. Some octopuses eat shells I believe, so that might help. They probably do mostly just decompose. The should totally be an animal that use shells it finds on the sea floor as armour. Likely an octopus that has a lot of control over the size of it's body.

 

Fun fact, there is an octopus that carries around two coconut shells or clam shells as shelter/armor. Also, octopuses did used to have a shell for armor but eventually lost it, and is likely why octopuses are so unique and awesome.

[Guest Somebody from Scadrial]

22 minutes ago, Aspiring Writer said:

Fun fact, there is an octopus that carries around two coconut shells or clam shells as shelter/armor. Also, octopuses did used to have a shell for armor but eventually lost it, and is likely why octopuses are so unique and awesome.

So it works better than I thought, Cool.

[Shard of Reading he/him]

9 hours ago, Aspiring Writer said:

Also, octopuses did used to have a shell for armor but eventually lost it

*Decides to write story about armored octopus*

[Condensation she/her]

Maybe I should...

That would be cool.

Did you know that there are many accepted pluralised forms of octopus? Octopuses, octopodes, octopods...

[Guest Somebody from Scadrial]

42 minutes ago, Ookla the Grammatical said:

Maybe I should...

That would be cool.

Did you know that there are many accepted pluralised forms of octopus? Octopuses, octopodes, octopods...

Actually there can only be two true ones, octopuda and octopuses.

[Condensation she/her]

1 hour ago, Somebody from Sel said:

Actually there can only be two true ones, octopuda and octopuses.

How do you know that?

[Guest Somebody from Scadrial]

1 hour ago, Ookla the Grammatical said:

How do you know that?

Octopus is a Greek combination, so it's plural would technically be octopuda, but it can also be considered an English word and would therefore have the plural octopuses.

[Condensation she/her]

Just now, Somebody from Sel said:

Octopus is a Greek combination, so it's plural would technically be octopuda, but it can also be considered an English word and would therefore have the plural octopuses.

But octopodes?

[Frustration]

Octopi.

[Condensation she/her]

Octopodes is better.

[Aspiring Writer]

Octopuses and octopi are the only one I have heard.

[Condensation she/her]

18 minutes ago, Aspiring Writer said:

Octopuses and octopi are the only one I have heard.

Octopodes is my favourite. It's because of the root, I think.

[Smye]

One particularly fascinating bit of info regarding: crab shell discards - throughout their lives they regularly shed their shells. Not only does this allow the crab to grow larger, but they concentrate heavy metals (such as led) in their shells, effectively chelating themselves every time they molt and shed their toxic load. Seems like something that would be exciting to work into worldbuilding.

Discarded shells are also dissolving at an increasing rate due to the rise of CO2 in the air precipitating a drop in ocean pH (in the form of carbonic acid).

Lastly, per the NIH, chitin (of which crab shells are composed) is the most abundant renewable polymer in the oceans and is an important source of carbon and nitrogen for marine organisms. The process of chitin degradation is a key step in the cycling of nutrients in the oceans and chitinolytic bacteria play a significant role in this process. These bacteria are autochthonous to both marine and freshwater ecosystems and produce chitinases that degrade chitin, an insoluble polysaccharide, to a biologically useful form. In this brief review, a description of the structure of chitin and diversity of chitinolytic bacteria in the oceans is provided, in the context of the significance of chitin degradation for marine life.

[Aspiring Writer]

9 hours ago, Smye said:

One particularly fascinating bit of info regarding: crab shell discards - throughout their lives they regularly shed their shells. Not only does this allow the crab to grow larger, but they concentrate heavy metals (such as led) in their shells, effectively chelating themselves every time they molt and shed their toxic load. Seems like something that would be exciting to work into worldbuilding.

Discarded shells are also dissolving at an increasing rate due to the rise of CO2 in the air precipitating a drop in ocean pH (in the form of carbonic acid).

Lastly, per the NIH, chitin (of which crab shells are composed) is the most abundant renewable polymer in the oceans and is an important source of carbon and nitrogen for marine organisms. The process of chitin degradation is a key step in the cycling of nutrients in the oceans and chitinolytic bacteria play a significant role in this process. These bacteria are autochthonous to both marine and freshwater ecosystems and produce chitinases that degrade chitin, an insoluble polysaccharide, to a biologically useful form. In this brief review, a description of the structure of chitin and diversity of chitinolytic bacteria in the oceans is provided, in the context of the significance of chitin degradation for marine life.

Wow. Thank you. Do you know how fast the shells degrade?

[Spren of Kindness she/her]

I don't know sciency stuff, but I see lots of crab shells on the beaches near where I live, so some of them end up there.

Edited December 17, 2020 by Spren of Kindness

[Condensation she/her]

I don't remember seeing any on the beach when we went for a week or so, but that could just mean that there weren't many crabs there.

[Smye]

3 hours ago, Spren of Kindness said:

I don't know sciency stuff, but I see lots of crab shells on the beaches near where I live, so some of them end up there.

Most of these are the discards from crab moults, rather than necessarily the leftovers from crabs being eaten. You can (roughly) tell by whether the eyes are still in place or if there are two eyeholes from where the moulting crab withdrew its allseeing orbs

[Condensation she/her]

2 minutes ago, Smye said:

Most of these are the discards from crab moults, rather than necessarily the leftovers from crabs being eaten. You can (roughly) tell by whether the eyes are still in place or if there are two eyeholes from where the moulting crab withdrew its allseeing orbs

Oh, cool! Good to know.

[Smye]

11 hours ago, Aspiring Writer said:

Wow. Thank you. Do you know how fast the shells degrade?

That's a rather complicated question, depending on the pH of the particular region of water they inhabit, the lifestage of the crab, the particular makeup of their carapace, etc etc. You may find this article helpful.

Additionally, while this is not my particular specialty (that would be education leadership and transition metal chemistry), I have found historically that emailing the author of a journal article a) REALLY makes their day and B ) yields an impressive level of help/education from the author... this is particularly useful when academic research is otherwise hidden behind a paywall.

Edit to add: It also depends on the particular critters inhabiting a given crab's region as marine bacteria are some of the primary utilizers of discarded chitin for their own purposes.

Edited December 17, 2020 by Smye

[Smye]

Also these (among others):

Full:

https://academic.oup.com/femsle/article/204/2/367/473284

https://www.frontiersin.org/articles/10.3389/fmicb.2013.00149/full

https://www.researchgate.net/profile/Nemat_Keyhani/publication/12721403_Physiological_aspects_of_chitin_catabolism_in_marine_bacteria/links/5a4ba331458515a6bc6ae068/Physiological-aspects-of-chitin-catabolism-in-marine-bacteria.pdf

https://aem.asm.org/content/aem/74/1/44.full.pdf

Behind paywalls (if you do bug the author, be kind, patient, respectful, etc):

https://link.springer.com/chapter/10.1007/978-1-4684-7612-5_10

https://link.springer.com/article/10.1007/BF00058835