Freshwater squid?

[Graeme]

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.

Why? Because cephs are a pre-Cambrian Class. Compared to other contemporary marine animals, I'd say they've been pretty successful, and quite comfortably sat in their niches, able to outcompete other animals that would perform a similar role. Really, cephs have always been quite a strong Class in natural history, and so probably never needed to migrate because they do the best job they can already. In fact, would it be too much to even suggest that migration to freshwater might have been because cephs filled their niches so well? That's maybe going a bit too far...

Then again, it might be something very simple such as they don't like constantly flowing water that they would most likely have to tackle first. True there are currents in the ocean, but they can move between water columns, thus escaping the flowing water. In a fast flowing river, you really have nowhere to hide from the current. Lotic waters are noted for being harsh environments, and maybe cephs just couldn't tackle this, either because of the conditions (given their very soft bodies) or because what little niches there were had already been swiped. Also, the first hurdle is possibly the most significant- estuarine environments are well-known for their turbulent waters. Marine water flowing up, freshwater flowing down generating strange currents. The varying conditions from intense stratification right up to "salt wedge" conditions. Estuaries are quite hazardous environments, even for hardy animals.

I couldn't see a migration from the sea to a lake as plausable- the animals would surely have to migrate up river systems.

 

[Taollan]

Why? Because cephs are a pre-Cambrian Class.

They are a Cambrian, the earliest mollusk that can be called a cephalopod is Plectronoceras from the upper Cambrian.

Then again, it might be something very simple such as they don't like constantly flowing water that they would most likely have to tackle first. True there are currents in the ocean, but they can move between water columns, thus escaping the flowing water. In a fast flowing river, you really have nowhere to hide from the current.

Well, A lot of the best places I have found giant Pacific octopuses are high-flow areas, such as a couple sites just outside Deception Pass in Washington. I don't know that it bothers them all that much. However, even so, some of the river that would most likely be first colonized by invading cephs would be very large, eutrophic rivers with a high biomass such as the amazon. The flow in much of the amazon is very gentle, almost lake-like.

Also, the first hurdle is possibly the most significant- estuarine environments are well-known for their turbulent waters. Marine water flowing up, freshwater flowing down generating strange currents. The varying conditions from intense stratification right up to "salt wedge" conditions. Estuaries are quite hazardous environments, even for hardy animals.

Graeme, I do believe you're brilliant and onto something great here. I really think we are asking the wrong question: "Why haven't cephs invaded freshwater", it should be "why haven't cephs taken on estuaries" Any migration to freshwater will have to go through estuaries. Not only do they physically separate freshwater environments and marine ones, but no animals is going to go from marine to freshwater in a single generation, there will be a series of (many) hypohaline tolerant animals before a true freshwater animal. So, why haven't octopuses taken on estuaries?

 

[Graeme]

They are a Cambrian, the earliest mollusk that can be called a cephalopod is Plectronoceras from the upper Cambrian.

consults sciency stuff. Ahh poo, you're absolutely right. My apologies; I feel quite foolish now

Well, A lot of the best places I have found giant Pacific octopuses are high-flow areas, such as a couple sites just outside Deception Pass in Washington. I don't know that it bothers them all that much. However, even so, some of the river that would most likely be first colonized by invading cephs would be very large, eutrophic rivers with a high biomass such as the amazon. The flow in much of the amazon is very gentle, almost lake-like.

Interesting. I've never heard of such behaviour. Are they resident to these areas, or perhaps just visiting? Would the sites serve as good feeding grounds? I wonder if they just brave the conditions, as it were, to get a chance at some good eating. Most invertebrate animals that live in flowing water are either extrememly flat and tend to be benthic, burrow or have tough exoskeletons or shells; or a conbination of these. Cephs have none of these adaptations. I'm not too sure as to the physical hardiness of cephs, but I'm guessing that they are quite fragile. I know quite well that octopuses have a high tenacity in their suckers to allow them to cling to substrata (ommitting squids and cuttles as their suckers are only good for one thing- prey capture), but would this result in the octopus losing its arm? I'd also have to consult my old scribblings on the subject- I can't recall the correlation between octopus suckers and pressure (I think it goes that increased pressure reduces the risk of cavitation), and am unsure if there is enough water pressure in a shallow, fast-flowing river to allow completely successful adherence. It would be interesting to see if marine vs fresh water has any impact on the ability of the sucker. If only I was still at uni, I could have went one step further and studied this!

Graeme, I do believe you're brilliant and onto something great here. I really think we are asking the wrong question: "Why haven't cephs invaded freshwater", it should be "why haven't cephs taken on estuaries" Any migration to freshwater will have to go through estuaries. Not only do they physically separate freshwater environments and marine ones, but no animals is going to go from marine to freshwater in a single generation, there will be a series of (many) hypohaline tolerant animals before a true freshwater animal. So, why haven't octopuses taken on estuaries?

Thanks Taollan. I dunno about the first bit, but I might agree with you on the second bit there We probably are trying to think too many steps ahead, instead of focussing on the initial steps which are the most important.
Maybe we should all bang our heads together and get a book published on the matter; just interesting arguements towards the case I can see it now... TONMO's first book: "What happened to the freshwater octopuses?"

 

[Tintenfisch]

(ommitting squids and cuttles as their suckers are only good for one thing - prey capture)

Not necessarily; I have a few spent/mated female onychoteuthid specimens covered in sucker marks. Plus, in at least one genus, the tentacular hooks (modified suckers) are thought to make cuts on the mantle into which spermatophores are implanted.
Not to be pedantic, of course, and not to hijack the thread...

 

[Taollan]

Ok, First of all, sorry about my absence for the last couple of days. Walla Walla was hammered by a wind storm and I have been without power since friday. (http://www.king5.com/localnews/stories/NW_010408WXN_easternwa_wind_storm_LJ.d0a3c96.html if you're at all interested)

Anyhow: to respond

Interesting. I've never heard of such behaviour. Are they resident to these areas, or perhaps just visiting? Would the sites serve as good feeding grounds? I wonder if they just brave the conditions, as it were, to get a chance at some good eating. Most invertebrate animals that live in flowing water are either extrememly flat and tend to be benthic, burrow or have tough exoskeletons or shells; or a conbination of these. Cephs have none of these adaptations. I'm not too sure as to the physical hardiness of cephs, but I'm guessing that they are quite fragile. I know quite well that octopuses have a high tenacity in their suckers to allow them to cling to substrata (ommitting squids and cuttles as their suckers are only good for one thing- prey capture), but would this result in the octopus losing its arm? I'd also have to consult my old scribblings on the subject- I can't recall the correlation between octopus suckers and pressure (I think it goes that increased pressure reduces the risk of cavitation), and am unsure if there is enough water pressure in a shallow, fast-flowing river to allow completely successful adherence.

These GPOs are resident in the area for about three months at a time before moving on. They have dens in the area and can be regularly visited, and sometimes seen out and about. The reason they may be there is the abundance of Pacific spiny scallops, Chlamys hastata, which are filter feeders and seem to like high flow areas. The octopuses in this area eat more scallops than red rock crabs, their second-most consumed prey item in the area.
Really I think that you are underestimating the toughness of octopuses. I really doubt an octopus would have a problem of flow up to 7 knots or so. In my younger and foolish days I was known to pull on the arm of a GPO with all my might, and there was no detatchment of the arm. In fact, even a small 10 pound individual seemed to be little more than annoyed. Later in my octopus experiences I have had 70 gram O. rubescens latch on to my hand with 4 arms, and onto their artificial den (with a one liter volume) with the other four. In an attempt to get the octopus to let go, I pulled my hand, him attached to it, and him attached to the den full of water, all out of the water and he held for about 10 seconds. Octopuses are incredibly strong for their size, and I seriously think even a stiff current would be little more than an annoyance, If it got too bad, octopuses are pretty good at flattening themselves out.

 

[DWhatley]

Taollan,
But for how long? There are many very fast animals in the wild but their speed (and possibly the octo's strength) is only for short bursts (I am particularly thinking of the Cheetah but there are numerous others). You mentioned your rubescens held on for 10 seconds but not 10 minutes. IF flow is a factor, endurance would be key.

PS Hope your tanks are OK with the power outage!

 

[Cairnos]

How well do cephs cope with temperature changes and extremes? I'm trying to think through the differences (apart from straight salinity) between sea and freshwater environments and one of them would be the (comparitively) rapid and extreme temperature changes that you would get in freshwater environments (except for large lakes and such).

In the eels would get any ceph which tried it, much like they go through just about anything else that takes thier fancy

 

[Steve O'Shea]

Rapid temperature change (or gradients) knock squid out almost immediately. It's never been pressure that has caused me problems (with cephs having a partially closed circulatory system - less prone to embolism), but the thermocline.

 

[Taollan]

Power seems to be restored back to Walla Walla in full now. Luckily the WWU campus never lost power, so the octopuses were safe. It did make me very nervous though and I had battery powered aerators and bags of ice on stand-by (the added harzards of keeping cold-water cephs).
Anyhow, you are right, endurance could be a problem, but I was trying to illustrate that the integrity of an octo's body won't be compromised by the forces caused by flow.

but would this result in the octopus losing its arm?

I still don't think flow would be a barrier to freshwater invasion. Like I have mentioned earlier, there are some very low flow freshwater systems with high biomass (lower Amazon, Mississippi, Mekong, most very large rivers), and some octos seem to handle tidal currents well (admittedly these are intermittent).
As for temperature, like SOS mentioned about squid, my experience has been that strictly subtidal species have a hard time with temperature changes. That being said, octopuses that frequent intertidal areas seems to be relatively tolerant. Again, that being said, my experiences have been with octopuses exposed to acute changes (on the order of 11-12C temperature change for the period of 6 hours) and not chronic like you would have seasonally in a temperate lotic system (say same temp range, but over 4 or 5 months). But again those same river systems that have low flow and high biomass have also fairly constant temperatures, especially the tropical ones such as the amazon.
As I think about this more, the more I think the question is: Why are there cephs in the intertidal but not estuaries?

 

[Crazy Kary]

Thank you for replying

Once again I claim to know nothing about squid. I'm thankful for the answers I got to my post. The only other comment that makes sense pertaining to what I saw is the threadfin shad doing some some sort of mating ritual. The backwaters where I fish have an abundance of these shad. The main times I see these shad is when bass are schooling on them so obvioulsy the only ritual they would be practicing then is escape. The thing that still bothers me is how close that fictional article sounded (including where these creatures would be found and the surrounding habitat cypress trees, crayfish, polluted waters). It very well could have been shad, but I still believe this should be investigated further because I knew nothing about this fictional article until after I had that experience. To anyone who is interested, there is documented proof of a bull shark being caught in a town called Simmesport, Louisiana some 2 years ago. From a North/South standpoint, that is as North as where I am fishing, just on the other side of the Mississippi River. If that guy wouldn't have caught that shark, no one would believe it could have gotten there. Ironically, the only other country to have documented bull sharks in freshwater is Brazil (in the Amazon). At least the only other country I know of.

 

[Animal Mother]

Once again I claim to know nothing about squid. I'm thankful for the answers I got to my post. The only other comment that makes sense pertaining to what I saw is the threadfin shad doing some some sort of mating ritual. The backwaters where I fish have an abundance of these shad. The main times I see these shad is when bass are schooling on them so obvioulsy the only ritual they would be practicing then is escape. The thing that still bothers me is how close that fictional article sounded (including where these creatures would be found and the surrounding habitat cypress trees, crayfish, polluted waters). It very well could have been shad, but I still believe this should be investigated further because I knew nothing about this fictional article until after I had that experience. To anyone who is interested, there is documented proof of a bull shark being caught in a town called Simmesport, Louisiana some 2 years ago. From a North/South standpoint, that is as North as where I am fishing, just on the other side of the Mississippi River. If that guy wouldn't have caught that shark, no one would believe it could have gotten there. Ironically, the only other country to have documented bull sharks in freshwater is Brazil (in the Amazon). At least the only other country I know of.

The shark may have been placed there by an irresponsible hobbyist who couldn't accommodate the animal anymore. There are reports of sharks popping up in strange places. Apparently they are surprisingly tolerant of low salinity conditions.

 

[DWhatley]

AM,
It is unlikely that a bull shark was anyone's pet (well, OK, mayby the hound os Tindalos ). However, bulls have been documented up stream on numerous occassions and there was a recent (to my eyes, may have been a repeat) documentary that mentions one that managed to eat a kid or two in Illinois long before I was born. Wikipedia has a reference to the Illinois siting as well as other notes on their freshwater travels.

Bull shark - Wikipedia

 

[Animal Mother]

I'm not all that familiar with all the different sharks honestly. All I know is much like crocodiles and alligators, people are dumb enough to think they can keep them, and then when they start growing really big and become uncontrollable they dump them wherever it's convenient.

 

[Tintenfisch]

There was an interesting talk at the NZ marine sciences conference last week about habitat use in bull sharks. Apparently they use the Australia's Gold Coast artificial canal system extensively, with the youngest age class actually preferring salinities of 6-18ppt.

Abstract attached.

 

[daddysquoc]

if i never mentioned this ur signature is rather hilarious Tintenficsh