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Freshwater squid?

Graeme

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#5
The only freshwater squid I have ever come across is the Elephant Squid.




... But then it was invented by Anthony "Doc" Sheils to explain hte Loch Ness Monster... :lol:



I don't think there is such a thing as a freshwater squid. Leastwise, not one known to science. Plus they are very successful in their existing niches, why would they need to move?
 

erich orser

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#6
Absolutely hilarious! I love straight-faced B.S. of this magnitude. :lol:
 

cthulhu77

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#8
It is simply a matter of respiration and food.

If you look at the complex of cephalopods living in the oceans (and trees, for those of you with fanciful natures), it is easily seen that the larger species live in deep water...the closer you get inshore (less absorbable oxygen), the smaller.
For a squid, or more likely, an octopus, to adapt to freshwater, it would have to me extremely small...and the food sources in freshwater aren't even close to what is available in the tidal areas.

Doubtful that it will ever happen.
 

monty

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#9
cthulhu77;98624 said:
It is simply a matter of respiration and food.

If you look at the complex of cephalopods living in the oceans (and trees, for those of you with fanciful natures), it is easily seen that the larger species live in deep water...the closer you get inshore (less absorbable oxygen), the smaller.
For a squid, or more likely, an octopus, to adapt to freshwater, it would have to me extremely small...and the food sources in freshwater aren't even close to what is available in the tidal areas.

Doubtful that it will ever happen.
I'm with you on food, might add salinity, but I'm not sure I buy the respiration thing: many cephs live in deep, low oxygen conditions, and do just fine; in fact, Gilly's work with Humboldts suggests that they're much better at coping with that than folks had previously thought. Ward's book Out of Thin Air I read recently posits (among many other oxygen-related animal evolution theories) that cephs evolved driven more by advanced respiration, and that jet propulsion and free swimming were side effects of just pushing lots of water over the gills... Although cephs need more oxygen for their active lifestyles, there are plenty of examples of freshwater bivalves and even terrestrial gastropods, so it's demonstrably not inherent in mollusc physiology that they can't survive in low-oxygen environments... and cephs tend to have much better coping mechanisms for low oxygen than other molluscs, like the separate hearts for the gills.

I suspect that vulnerability is an issue, too: cephs don't do well drying out, and they're not well-suited to living in small pools (since we know how much food they require and waste they produce!), and they're vulnerable to predation by birds in shallow freshwater.
 

tonmo

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#10
This thread was referenced here. :cool:
 

Spence24

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#11
And isn't the whole thing about feeding your ceph freshwater food that it is so low in nutrition they eventually just start to waste away???
 

Taollan

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#15
monty;98641 said:
I'm with you on food, might add salinity, but I'm not sure I buy the respiration thing: many cephs live in deep, low oxygen conditions, and do just fine....
Boy, this is one of those questions that really fascinates me... why haven't cephs gone to freshwater (along with why is semelparity adaptive in octos...)
I have to disagree with the not enough food part. While freshwater does have lower bimass overall that marine environments, there are some that have quite high primary production and very high biomass, such as the Amazon river and its tributaries, the Mekong river etc. Even in North America native freshwater mussels can be very abundant, (Margaritifera falcata reaches densities of 39 individuals per square meter , with average individual size about 8cm). These areas are comparable with many tropical marine areas (not coral reefs), which are relatively barren and have low primary productivity. Cephalopods seem to do fine in the deep sea as well, which has a much lower biomass density than many freshwater.
I really don't buy much into the respiration argument either. Nearly all surface waters (down to a 50 m or so), be it freshwater or marine, are oxygen saturated. Saturation level is dictated by water temperature. So really this isn't a problem. Rainbow trout have similar respiratory levels and thrive in freshwater. And it isn't a problem with extraction efficiency, as octopuses can extract up to 76% of the oxygen from their ventilatory stream in normoxic conditions.
I would tend to agree with Monty that it is likely partly a osmoregulation problem. But seriously, there are some cephs that frequent intertidal areas, like O. rubescens, that seem to be fairly resilient to reasonable salinity changes. Additionally, gastropods, the mollusks most closely related to cephs, haven't seemed to have had trouble invading freshwater or terrestrial environments.
I would also say variability in temperature would be another problem in freshwater for cephs, but then again we have cephs that frequent intertidal areas that seem to be fairly resilient to this as well. I will use O. rubescens as an example again, I have seen them go from 11 C to 0 C in the space of three hours, stay down there for about four hours and brought back up to 11 C again over the course of another three hours, and went on to live a long (for an octopus) life. That was as accute change, but O. rubescens occurs from Alaska to the Sea of Cortez, so that suggests that they physiologically can handle a large range of temperatures.
Anyhow, thats my :twocents:. Sorry if that was a bit long, But I find this all really interesting. I have a hunch if some research was to dedicate a descent about of time on the question, they would uncover some really interesting stuff about ceph physiology.
 

Graeme

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#16
Interesting point about intertidal areas. One thing of note however is that estuarine waters are invariably saline, albeit in fluctuating concentrations. In light of this, it is very likely that cephs in these environments will never actually encounter purely freshwater areas, at least for any length of time. I wonder if osmoregulation, or maybe another problem brought on by salinity levels (bouyancy, possibly?) is to blame? Granted, cephalopods are very similar to gastropods, but given that they fall under the phylum Mollusca, which is more varied than even our own phylum, Chordata, I believe the divide between gastropods and cephalopods is great enough for difference in physiological adaptations.

Of course it could just be entirely down to something as simple as niche allocation. It is entirely possible that any niche the cephalopod could fit in freshwater environments is already taken up by another animal, thus ousting the ceph from filling the niche.
 

Taollan

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#17
The gastropod bit was a stretch, but in my defense, gastropods and cephalopods are (relatively) closely allied within Mollusca. Obviously, since gastropods have invaded those evironments and cephs haven't, they are enough different to for those differences to be meaningful (is that sentence just as clear as mud?). Physiological, however, gastropods and cephs are very similar and if you want to compare cephs to something else physiologically, gastropods are it. So I think it is informative to look for small differences between the two for this question.

I do like you idea about niche competition, but really off the top of my head it would seem the incredibly higher diversity of forms in marine habitats would mean that niches would be all that more closed in marine than freshwater. Freshwater is filled with a few generalist species occupying a wide range on niches that often are occupied by ten times the number of specialist species in the ocean. Also, freshwater habitats is very ephemeral in the evolutionary sense, rapid changes are often leaving large niches open. Then again these quick changes might be part of the problem with ceph invasion. But that answer just beings us back to our original question: other animals do it, why not cephs.

I have on more idea here. Perhaps it is the lack of diversity in the food base in the freshwater that is the problem. Many octopuses have trouble thriving on a monotypic diet... I am not sure I like that explanation either....
 

cuttlegirl

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#18
Taollan;107254 said:
I have on more idea here. Perhaps it is the lack of diversity in the food base in the freshwater that is the problem. Many octopuses have trouble thriving on a monotypic diet... I am not sure I like that explanation either....
Many of us have fed our cephalopods fresh water shrimp, so it is possible for them to prey upon fresh water species.

I am wondering if it has something to do with their high metabolism.

I find it interesting that mammals like the Baikal Seal and the freshwater dolphin species have survived in freshwater environments (although they are now threatened by human pollution...).
 

Taollan

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#19
cuttlegirl;107258 said:
I am wondering if it has something to do with their high metabolism.
There are freshwater fishes that have comparably high metabolism. So I don't think that is the case. What you brought up about freshwater dolphins and Baikals seals is very interesting. Being warm-blooded mammals, they have a much higher metabolism per body weight than octopuses, and thus have a higher food requirement as well. However, since there is relatively little water exchanged through the skin with mammals, osmoregulation is going to be wildly different than with most invertebrates such as octos...
 

monty

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#20
cuttlegirl;107258 said:
Many of us have fed our cephalopods fresh water shrimp, so it is possible for them to prey upon fresh water species.

I am wondering if it has something to do with their high metabolism.

I find it interesting that mammals like the Baikal Seal and the freshwater dolphin species have survived in freshwater environments (although they are now threatened by human pollution...).
I like the re-awakening of this thread!

It seems like marine mammals have a rather different approach to osmotic regulation than many other marine animals, in that they tend to keep the land-evolved systems isolated from the water as much as possible, while gill-using animals tend to, by necessity, have a lot of membrane exposure to salt water directly. I'm not sure how marine mammals get hydrated, though.

The fact that so many octopuses live in intertidal zones sure does fly in the face of most of the arguments for why they have never moved into fresh water... another thing that no one has mentioned recently is that cephs are a very ancient group, and I know that the ocean's salinity is believed to have been appreciably less in the Cambrian, so there's some evidence that early shelled cephs existed in lower salinity conditions.

Has anyone else read Peter Ward's Out of Thin Air book? It's overall about how oxygen levels have been a major and often overlooked driving force for evolution (with many hypotheses that Ward advocates looking at, with appropriate caveats that some may well be wrong... it's a food for thought book.) One of the variants of this story is the hypothesis that cephalopod development of jetting and neutral buoyancy, and hence effective predation, was secondary to development of better respiration: that the mantle inhalation and exhalation through the siphon was to get better circulation of low-oxygen water past the gills, and that had the secondary effect of jet-swimming and higher possible metabolism, which offered an opportunity to prey on the oxygen-starved slower critters in the environment, which nudged the evolution in the direction of free swimming, improved jetting, neutral buoyancy, and tentacles to grab lunch. He also suspects the segmentation of trilobites was more about repeating the body segment that has the gill than anything.

I had already been thinking that the presence of so many cephs in deep, low-oxygen water makes many of the "traditional views" of hemocyanin as inferior to haemoglobin is vertebrate arrogance, particularly in light of Gilly's lab's demonstrations of active, fast, huge humbodts spending a lot of time in the anoxic layer, and reports of nautilus having a good ability to survive low-oxygen and even out-of-water conditions. Ward's book, however, really got me thinking a lot more about the inconsistencies of things I'd read, like "the teleost fishes were able to drive the cephalopods to deeper water because their metabolism was much more effective due to haemoglobin and better oxygen storage in tissues." I'm sure this is true up to a point, but the fact that the cephs are the ones who were more successful in the low-oxygen depths suggests that rather than being metabolically challenged, the cephs outcompete vertebrates more readily at low oxygen levels, so the vertebrate respiratory and metabolic systems may be more tuned to current atmospheric oxygen levels rather than universally "better."

I suspect that cephs' mechanisms for handling low oxygen levels are more in the domain of "less well understood" than vertebrates' systems, and there's a tendency to assume "not understood" is "inferior." I'm not sure how osmotic regulation occurs in any mollusc, or how freshwater bivalves and gastropods differ from their marine counterparts in mechanisms for maintaining homeostasis in freshwater environments, and likewise for terrestrial gastropods. I note that table salt is lethal for slugs, snails, and leeches. Is vastly over-salted water lethal to marine molluscs in a similar way? How about freshwater molluscs in marine salinity levels?

Asking why there are no freshwater cephs seems to also just be a reminder of the huge gaps in our understanding of the history of the modern cephs: the almost complete lack of soft body fossils, and consequently our lack of understanding of the prevalence of non-shelled cephs at various points in their evolutionary history-- which raises a question of whether it's easier, harder, or the same for a shelled ceph to migrate to freshwater (where the pumps in the siphuncle and chamber fluid composition might be impacted) or for a coleoid (where it's harder to be neutrally buoyant in freshwater than denser salt water, although octos, for example, seem happy enough to be negatively buoyant.)

I'm not really buying the "all the niches were occupied" argument as an absolute argument, although it may be sort of a "luck of the draw" argument... It seems like cephs were dominant predators in the ocean before vertebrates had established themselves anywhere, certainly not on land. I'd assume that plants and arthropods, and maybe gastropods, had to be well established on land well before vertebrates... if anything, all the hungry ammonites probably provided pressure for arthropods to escape to dry land. Anyone know if there's a fossil record of when the first terrestrial or freshwater gastropods emerged?

A related question someone asked me that may appeal to the readers of this thread is "how come the queen/drone/worker/hive arthropod model that's so successful for insects on land doesn't seem to occur in marine arthropods?" unless there are examples in marine arthropods that I'm unaware of...

And as long as we're asking such questions, perhaps considering why there are no terrestrial or freshwater echinoderms would be interesting as well... I'd think a starfish or sea urchin would be at least as good a candidate as a snail for crawling about on dry land and eating plants and lichens and such off of rocks.
 

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