Sadly, Lake Squid Don't Exist
    By Danna Staaf | March 28th 2012 09:51 PM | 10 comments | Print | E-mail | Track Comments
    About Danna

    Cephalopods have been rocking my world since I was in grade school. I pursued them through a BA in marine biology at the University of California...

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    One of the more whimsical squid news stories I've seen in a while: A squid, a dog, and a mini-mystery solved at a Minnesota lake.

    "Of course, squid are not found in Minnesota lakes," reports journalist Al Edenloff. So true, and so charmingly put!

    Squid are not found in any lakes. Neither are octopuses, cuttlefish, or nautilus. Class Cephalopoda is exclusively marine, with the closest approximation to a freshwater representative still only tolerating a wee bit of rain with its seawater. Other mollusc groups, like snails and mussels, have members in both salt and freshwater--but not cephalopods. What's the diff?

    Cornell's Ask A Scientist addressed this question back in 2005, but I find the answer rather unsatisfying. Dr. Vawter just explains why freshwater snails are good at coping with freshwater, without explaining why cephalopods haven't evolved the same tricks. Commenters at TONMO and Why Evolution Is True have also weighed in, but to my knowledge science hasn't yet got a clear answer.

    At least the Minnesota mystery has a satisfying resolution!


    Bonny Bonobo alias Brat
    Hmm, interesting, why are there no fresh water squid? The Ask MetaFilter website makes the following 2 suggestions :-
    I suspect it's because of how they reproduce. Tens or hundreds of thousands of them collect together in a single location and everyone lets go at once. The resulting murk in the water contains billions to trillions of fertilized eggs, the vast majority of which won't make it to adulthood. The survival rate is very low, but the number of eggs released is so huge that enough make it for the next generation. They're relying on overwhelming the predators who prey on their young through sheer quantity.In fresh water settings (e.g. rivers), not enough squid could collect together, and the fertilized eggs wouldn't be produced so that a sufficient quantity could survive predation. I suppose it could be done in a really large body of fresh water (e.g. Lake Michigan) but there aren't enough of those kinds of bodies around, and they're not easily accessible for squid to migrate to.
    It's difficult, evolutionarily speaking, to make the transition from salt water to fresh water. If you take a salt water fish and drop it into fresh water, it'll explode over the course of an hour or two. (Putting a fresh-water fish in salt water causes it to die of dehydration.) Migrating from the Atlantic Ocean to Lake Michigan would be a trip taking thousands of years, and the squid would have to become adapted to reproducing in a river first. (Then they'd have to figure out how to get up Niagara Falls.) 
    I remember as a child coming across thousands of frogs copulating in the canals where we played around in hired rowing boats (mainly sinking them) and they produced gallons of frog spawn, so surely they were no different to squid gathering in huge numbers, yet it worked well for the frogs reproducing in freshwater, so why wouldn't it work well for large numbers of squid?
    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at
    Danna Staaf
    Both interesting ideas, but I don't think either has much explanatory merit. In the first case, the author doesn't understand how squid reproduce. Yes, many squid have mating aggregations, but not all species do, and those species who do aggregate do not release their fertilized eggs loose into the water. Rather, they produce capsules of fertilized eggs which are then attached to the substrate. There are no squid that I know of who engage in the kind of "broadcast spawning" described by that writer.
    And, as you point out with your example of the frog orgy, spawning aggregations in freshwater are quite common. I don't think their mating strategy is what's holding squid back.

    In the second case, the writer isn't really saying anything specific to squid. Yes, it's true that there are challenges associated with the transition from saltwater to freshwater (as there are for any environmental change) but many, many animals have evolved solutions to those challenges. Simply saying "it's hard" doesn't really answer the question.

    Thanks for tracking these down and posting them!
    And not in swimming pools either:

    City Diary: Goldman’s vampire squids must leave the pool

    Robert H. Olley / Quondam Physics Department / University of Reading / England
    Do the closely related freshwater mollusks still have the copper based blood. A quick search showed that at least some freshwater snails have a hemoglobin based blood vs hemocyanin.

    Danna Staaf
    Ooh, interesting idea! So, it looks like of the dozens of snail families that inhabit freshwater, only one has evolved hemoglobin. These authors point out:
    The only other known gastropod that has hemoglobin is the deep-sea vent caenogastropod Alviniconcha hessleri, which harbors the red pigment in its gill to support endosymbiotic bacteria.
    So, hemoglobin exists in both freshwater and saltwater snails, but it's very rare in both cases.
    Where is seems I saw the reference to the only "snail" with iron based blood, the article goes on to suggest that many clams have switched and even suggests the switch is was to deal with fresh water:

    "Also, various clam species possess high-affinity hemoglobin that is closely related to their respective myoglobin, but most hemoglobins in bivalves are small and intracellular; the only known exceptions are the huge 14- to 24-domain rodlike hemoglobins in Astarte and Cardita (26, 27). In the deep-sea clam Calyptogena kaikoi, the major physiological role of hemoglobin is apparently storage of oxygen under low-oxygen conditions rather than circulating of oxygen (28). As suggested by Mangum (29), hemocyanin probably is not able to evolve into high-affinity forms, in contrast to hemoglobin. An alternative scenario is suggested by the existence of the truncated BgHc (see Fig. 2). Of course, the underlying mutations might have happened after hemocyanin was replaced by hemoglobin, but what if these mutations occurred first? This incomplete hemocyanin still may have served for oxygen transport in a limited way, which was once sufficient for a terrestrial life but became a handicap, needing to be replaced when the terrestrial ancestors of the planorbids colonized freshwater habitats (20). "

    It would be interesting to monitor an octopus as the salinity slowly decreased to try to determine what starts to fail (but not MY pets of course). I recently read an article outlining attempts to grow young vulgaris for food in cages in a shallow bay (not an attempt at raising from eggs). The project was successful until heavy rains killed all of them and the expectation was that the resulting low salinity was at fault. The summary appeared anecdotal thought as no mention was made of testing the water for run off pollutants or other possible causes.

    Danna Staaf
    Hmm. So, I don't read that as saying that hemoglobin is specifically an adaptation to freshwater. As I understand it, they'res saying that in the case of both the snail and the clam, hemoglobin helps them in low-oxygen environments, which can be either freshwater (ponds) or saltwater (deep sea).
    The final sentence, suggesting that hemocyanin "needed to be replaced," is actually talking about the transition from terrestrial to freshwater, not saltwater to freshwater. The ancestors of these weird hemoglobin snails moved first from saltwater to land (where they lived like modern garden snails), so they were actually air-breathers, and then when they switched back to breathing water, they had to make some adjustment from what they were doing to breathe air.

    You're right that it would be interesting, but slightly sadistic, to figure out exactly what fails in cephalopods as water becomes fresher. I've heard several anecdotes like the one about the vulgaris, and in no case does anyone seem to test for pollutants--they just assume it's a freshwater kill.
    The discussion rekindled my curiosity. I have some infertile octopus eggs that are well over a month old. I removed them as soon as they were laid to see how long it took for them to naturally deteriorate with the idea that they are normally eaten rather than disintegrating . Obviously, they don't rot easily in saltwater when left alone ;>). The discussion motivated me to split them and place half in freshwater. It would likely have been better to do this when I retrieved them but "at home" laymen experiments are just to generate ideas ;>)

    Danna Staaf
    Many of my early grad school experiments were kind of like that. =) I'd love to hear what happens to the freshwater/saltwater eggs!
    So far, no difference ;>)