Anyone know about cephalopod den behavior?

[Spy D]

Thanks in advance for any responses. I'm researching for a screenplay and want to know the nesting behavior of octopi. Specifically, if there was a sunken hull of a ship, would any cephalopods (hopefully less than a meter in length, octopus/squid-like in appearance, and found in the region bordering Indonesia and the open Indian Ocean) share this den with others?

I imagine my scuba-diver entering, discovering the skeletal remains of slaves still chained to the walls, and in her sudden withdrawl, disturbing a large number of cephalopods that basically swarm (and possibly glow with bioluminescence). I want them to be startling and potentially dangerous (or possibly just beautiful should they be bioluminescent), but not guaranteed to attack so that my character can retreat and escape more or less unharmed.

Is it realistic to imagine Sam entering and shining her light without immediately disturbing them?

That's a tall order, I know! It's just a small moment in the story and not a plot point, so it doesn't need to be exact. Anyhow, any advice is much appreciated. Thanks! -Spy D

 

[mucktopus]

I imagine my scuba-diver entering, discovering the skeletal remains of slaves still chained to the walls, and in her sudden withdrawl, disturbing a large number of cephalopods that basically swarm (and possibly glow with bioluminescence). I want them to be startling and potentially dangerous (or possibly just beautiful should they be bioluminescent), but not guaranteed to attack so that my character can retreat and escape more or less unharmed.

Is it realistic to imagine Sam entering and shining her light without immediately disturbing them?

It's pretty much already unrealistic to imagine most of the above scenario, so i don't see why Sam entering without disturbing them is a limiting factoid. Of course if you wanted to create this scene in the wild with real animals, then that will be a problem. Squids and a couple of shallow-water cuttlefish are about the only cephs that would swarm, and they wouldn't really hang out inside the hull of a ship. A few types of octopuses might inhabit a wreck, but they wouldn't swarm. Octopuses are generally asocial. There is one type of octopus that aggregates to brood eggs, but it's found well beyond the limits of scuba. I can't think of any bioluminescent cephalopod that lives within the reach of a scuba diver. Other people might have different opinions, but I feel if this is staged with fake animals - then go for it- it's already so creative that you shouldn't be too concerned about the facts.

 

[Steve O'Shea]

Hmmmmmm. Interesting, though I'm inclined to agree with "Mucktopy".

So, you're talking conventional SCUBA depth, < 40 metres (~120 feet)?

An when you mention 'screenplay', are you talking theatre or film?

Oh, and a warm Spy, by the way.

 

[erich orser]

Spy! Personally, especially in that region, I'd go with cuttlefish.

 

[Spy D]

wow! thanks for responding, all three of you. this is a screenplay and i must say from the start that for this story i am truly breaking the old adage 'write what you know' (for one, i'm not a diver). I do care, though, about keeping fairly close to the realm of reality. i always hate in movies when something i'm familiar with is portrayed in a completely unrealistic way. it pulls me right out of that world. so i'm trying to get it right.

anyhow, the year is 1976 and sam is an accomplished scuba diver (we find her teaching deep water rescue/recovery to sheriffs, but by some opinions she is wasting her talent doing this) and is recruited by her estranged treasure hunter ex to find the famed explorer pablo cerrado's legendary lost ship of gold near a remote volcanic island.

the ship they find and the one sam enters (not cerrado's, but the sunken slave ship from the opening scene) i've placed at 200 meters down and stuck in a fissure. if a diver were to dive to this depth, what would be the decompression time if they returned after five minutes there? after one hour? i realize this is a huge amount of time at this depth (she will be assisted), but i'm not sure if it's just unreasonable. the ship could be in shallower water (this area of the sea has not been searched before, so it doesn't need to be especially hard to find), but since she'd be one of just three people loading a lot of gold, i figure they couldn't possibly do the job in less than an hour. in actuality, sam is only there for five minutes before starting to decompress, but going down, she doesn't know that'll be the case.

i am way off the topic of cephalopods. my apologies if i'm violating the parameters of the forum (i get the sense the people here are pretty laid back). anyhow, thanks for the great responses. i look forward to your insight. -spy d

 

[tonmo]

i am way off the topic of cephalopods. my apologies if i'm violating the parameters of the forum

Thanks -- you're not in violation. The rule is that all SEED posts (i.e., the one you started this thread with) must be related to cephalopods. Replies to seed posts must stay on topic with the thread, but the responses themselves do not necessarily have to be about cephs. Since this question is asked so often I've added a Forum Announcement explaining core policies (long overdue!)

Thanks for you concern, and good luck w/ your screenplay!

 

[monty]

Sounds like a very cool movie, and as a movie viewer, I really appreciate writers trying to research things in depth, since the "suspension of disbelief" issue is a big one for me, as well! Please keep us informed so we can see it on opening weekend!

the ship they find and the one sam enters (not cerrado's, but the sunken slave ship from the opening scene) i've placed at 200 meters down and stuck in a fissure. if a diver were to dive to this depth, what would be the decompression time if they returned after five minutes there? after one hour? i realize this is a huge amount of time at this depth (she will be assisted), but i'm not sure if it's just unreasonable. the ship could be in shallower water (this area of the sea has not been searched before, so it doesn't need to be especially hard to find), but since she'd be one of just three people loading a lot of gold, i figure they couldn't possibly do the job in less than an hour. in actuality, sam is only there for five minutes before starting to decompress, but going down, she doesn't know that'll be the case.

At 200m, there are worse problems than decompression to worry about. At the pressure at about 100m, if you breathe the sea-level air mixture, the partial pressure of oxygen is so high that it becomes toxic... the immediate problem being that it leads to convulsions, unconsciousness, and the like. Although it is possible to avoid this by breathing mixtures other than air, that have a lower fraction of oxygen (usually mostly helium, since nitrogen at high pressures causes the bends) this is pretty complex and I don't think it's done regularly (maybe recovering treasure is a specific task that it would be used for, along with submarine rescues)-- maybe some specialized commercial dive companies are equipped for it, but if so, I don't know about that. Remember that if you do breathe a mixture like this at depth, it would not have enough oxygen at the surface, either, so you'd need to breathe from an air tank down to some pressure, and then switch to the specialized mix, or something like that.

With respect to decompression, the sport dive table I have convenient shows 150ft-190ft as 5 minutes at depth being the no decompression limit (the worst category) even assuming the first dive. But the bottom time is pretty limited before then-- at 100ft, you only get 25 mins before you need decompression. The sport dive tables can show the decompression needed for various bttom times at up to 190ft; rather than me quoting them, you should pick one up in a sporting goods shop or borrow/xerox one or something. (you can find some dive tables for no-decompression dives online by googling "dive tables" but I didn't find one that included the decompression stop table in the first few pages. I did find a link to a 948 page US Navy dive manual in pdf (50MB) that would probably tell you a lot more than I can, though: http://www.vnh.org/DivingManual/DiveManRev4ChangeA.pdf )

Another good site (dive medicine, mostly) is: http://www.diversalertnetwork.org/medical/index.asp

I also found some interesting stuff at these two sites:
http://www.hyperchamber.com/dive_tables/
http://www.reefscuba.com/tablesphysics.htm

At 200m, there might be more exotic cephs than what people were thinking about "at SCUBA depths," however, although I don't know of any schooling cephs that like enclosed spaces at all... but I am not a teuthologist, or even much of a diver lately... all this looking at dive tables is making me realize I need a refresher course!

 

[Spy D]

Monty- Wow! Thanks so much. That is amazing for you to have spent such effort to clarify things for me. I will check out the dive tables and this motivates me to go to the local dive shop and ask questions as well (I might even take the basic open water cert). I looked into some alternative gas mixtures after reading your post. I'm not sure if heliox would suit such a deep dive (I am open to modifying the details of my story, of course), but you've given me a great start.

Everyone- Thanks for posting! If I have more cephalopod questions, I absolutely will start here. If you see a movie about a beautiful red-haired diver and a volcanic island inhabited by the descendants of escaped slaves, know that you deserve some of the credit (or blame, depending. :] ). Take care. -Spy D