ARCHITEUTHIS BUOYANCY AND FEEDING
Here we present a little scientific evidence supporting our contention that Architeuthis is a rather passive beast, rather than aggressive hunter, much like the Humboldt squid. Within its tissues Architeuthis balances the ration of ammonium ions to sodium ions to achieve buoyancy. The sodium ion (Na+) has a relative atomic mass of 23 amu, while the ammonium ion (NH4+) has a relative atomic mass of 18 amu; ammonium ions are therefore lighter than sodium ions. Tissues taken from various parts of a fresh Architeuthis individual, from the tip of the mantle through to the tips of the arms, manifest variations in ammonium- and sodium-ion levels (Figures 1, 2). The ratio of ammonium to sodium has a maximum in the mantle and a minimum at the arm tip — it is not constant throughout the tissues. This implies that (the adult) Architeuthis suspends itself in the water column at an oblique angle, rather than on the horizontal plane. The animal’s fins and mantle would be up, its arms down, and the two long tentacles would drop almost vertically, clasped together, with their distal, expanded clubs acting as tongs would do, plucking prey from the water column many metres away.
A crude test for the presence of ammonia in Architeuthis tissues has been detailed elsewhere online, but the technique entails cutting a small piece (~ 1 cm cubed) of tissue and placing it into a narrow-necked flask (test tube or other such glass container), to which several crystals of caustic potash (potassium hydroxide) are added, the container heated, and emissions sniffed; if ammonia is present you’ll smell it. Using this test suggested that Architeuthis suspended itself at an oblique angle in the water column, rather than swimming parallel to either seafloor or surface. A more analytical approach to determining relative ammonia levels in various parts of the Architeuthis body was undertaken on a fresh-dead (recently caught and frozen) specimen.
Figure 1: Example chromatogram showing the peaks related to each cation.
Figure 2: Ammonium to sodium ratio with tissue site.
The mean ratio of ammonium to sodium ions (n = 4) was determined for each tissue sample. The ratio of ammonium to sodium has a maximum in the mantle and a minimum at the arm tip, indicating that levels of ammonium and sodium are not constant through out the tissues and that Architeuthis is oriented in the water column at ~ 45° angle, mantle up, arms down.
This theory finds quite independent support in an observation made by Mike Smith, the skipper of a New Zealand registered fishing vessel, F.V. Cook Canyon. Mike observed on his depth sounder, and captured in his net an Architeuthis. On his depth sounder a large structure was observed, suspended at an angle of about 45° in the water column, about 5–10 metres above a school of hoki. Upon retrieval of the net it was deduced that this large echo-sounding object was the mature Architeuthis in the net.
For Architeuthis to orient itself naturally at an oblique angle in the water column it would prove difficult for it to feed in any way other than by dangling its tentacles below in search of prey. Being so long and delicate (~ twice the length of the mantle and head combined), it would prove difficult for mature animals to co-ordinate propulsion of these structures to prey items ~ 8 metres away. It is far more likely that mature Architeuthis feed by suspending the tentacles into schools of fish below, clasping them together and leaving only the distal-most tentacle clubs free (Figure 3−5), splayed out like tongs to clutch any prey that inadvertently swims between or touches them. The structure of the tentacle stalks supports this theory. They have alternating, opposite sucker and studs distributed the length of each tentacle — opposing suckers fit neatly into studs. This character would be quite redundant were the tentacles not held closely together (Figure 3). Further structures, here referred to as ‘Lu bumps’, run the length of the flattened, inner face of the tentacles, which would assist in their interlocking by providing a rough texture (as opposed to a smooth surface).
Ammonium ion values reported for the tentacle of Architeuthis (Robison 1989) were considered similar to those from the arm and mantle earlier reported by Clarke et al. (1979). In terms of their protein and water content, the Architeuthis samples were much more akin to Loligo than to the watery, soft-bodied Vampyroteuthis and Bathyteuthis (the latter generally considered to be a slow-moving, sluggish squid).
Architeuthis has generally been assumed to be a relatively weak swimmer because of poorly developed musculature, loose structural morphology, and the low oxygen carrying capacity of its blood (Robson 1933, Roper & Boss 1982, Brix 1983). However, analysis of chemical composition patterns in mid-water fishes and crustaceans have shown high levels of protein in conjunction with low water content are correlated with higher locomotory capabilities and metabolic activity levels (Childress & Nygaard 1974, Childress et al. 1980, Bailey & Robison 1986). If the same is true of mid-water cephalopods, Robison (1989) concludes that Architeuthis may be a relatively good swimmer.
Gut content analysis repeatedly reveals squid, fish and crustaceans are the principal components of this animals diet. Unfortunately, gut contents are so fragmented that reliable prey identification cannot be made (as the oesophagus passes straight through the brain, all food entering the system must first be cut up into tiny pieces) -- although some rather interesting information about the diet of Architeuthis will be published in early 2004 (Bolstad & O’Shea, in press).
Figure 6. Schematic average ammonium-ion concentration levels throughout the Architeuthis body.
Bailey, T.G.; Robison, B.H. 1986. Food availability as a selective factor on the chemical composition of midwater fishes in the eastern North Pacific. Marine Biology 91: 131−141.
Bolstad, K.S.; O’Shea, S. (in press). Gut contents of a giant squid Architeuthis dux (Cephalopoda: Oegopsida) from New Zealand waters. New Zealand Journal of Zoology.
Brix, O. 1983. Giant squids may die when exposed to warm water currents. Nature, 303: 422−423.
Childress, J.J.; Nygaard, M. 1974. Chemical composition and buoyancy of midwater crustaceans as functions of depth of occurrence off southern California. Marine Biology 53: 259−276.
Childress, J.J.; Taylor, S.M.; Calliet, G.M.; Price, M.H. 1980. Patterns of growth, energy utilization, and reproduction in some meso- and bathypelagic fishes off southern California. Marine Biology 61: 27−40.
Clarke, M.R.; Denton, E.J.; Gilpin-Brown, J.B. 1979. On the use of ammonium for buoyancy in squids. Journal of the Marine Biological Association of the United Kingdom 59: 259−276.
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Robson, G.C. 1933: On Architeuthis clarkei, a new species of giant squid, with observations on the genus. Proceedings of the Zoological Society of London 1933: 681−697.
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