Just to put it out there, MikeAdams#367 just provided me with the following information:

Typical cells are about 70% water, while jellyfish are typically listed as being 95% water. Assuming the non-water components are approximately the same in make up in both cases, then the jellyfish would be about (with rounding errors): Oxygen 85% Hydrogen 9.5% Carbon 3% Nitrogen 1.5% calcium 0.2% phosphorus, 0.15%  potassium 0.06  sulfur 0.04  sodium 0.02  magnesium 0.01 + many trace elements

Unfortunately, all sources pertaining to what, exactly, a jellyfish is made out of have been fairly vague. All give a water percentage of between 95 and a little higher than 98 percent, the rest being listed irritatingly as "trace" or "other" elements. The little information I have found specific enough to consider valid has been varied. I read in one source that measuring the chemical composition of a jellyfish is difficult, as it is often in a state of flux and may even be influenced by what the jellyfish eats. So who knows, but I myself would like to see a little material on the matter. I sense a new question coming on.

As for my innitial question, I shall declare case solved. I did a little digging and found that the jellyfish I saw that day were of the genus Aurelia, which encompasses any one of the species of the very common, non-stinging moon jellies. I found a paper online about the life and reproductive cycle of one of these species (go to http://www.seaturtle.org/PDF/Lucas_2001_Hydrobiologia.pdf), in which it is written:

In most situations adult medusae shrink and die following spawning. It is thought that this is caused by extrusion of gastric filaments during gamete release, resulting in morphological degradation and susceptibility to parasitic invasion

So there we are.

>Excuse me, apparantly it turns out that most jellyfish consist, corporeally, of about 95% water (though some sources claim for it to be as high as 98%), with the rest of what's in there being mostly just trace elements.<

Mmm...  95% might just make the cut I suppose, though I still would love to see some well-controlled measurements, but anything less than the osmotic pressure of seawater I would want to see some serious physiological explanations as well as figures. And the Med is a pretty salty stretch of water, especially in the East. Without ever having tried to establish anything of the kind, I would have expected 90% to be nearer the mark. The trace element idea doesn’t hold water as stated. Apart from organic material, I would expect appropriate quantities of the macronutrients such as N, Mg, P, S, K, Ca, Fe, and of course Na and Cl. The total trace element content shouldn’t be more than a few hundred ppm.

>And believe me, they dissolve rapidly; I once left a freshly dead jellyfish in the shower (I was a strange child), which within less than an hour's time left not a trace of itself to be found but a slightly viscous liquid and an astronomically rancorous stench.<

Well, strange children make strange discoveries. Or so I am told...

I cannot remember who told me...

However, I cannot help wondering whether the fresh water might have played a role. I have found large, very dead jellyfish on beaches taking days to vanish under dry sand and other muck if they were not where scavengers such as snails would eat them.  

>From this I deduce that, had the tentacles had enough time to dissolve, the rest of their bodies would have had time at the very least to be floating around in partial decay.<

I wasn’t really thinking of “dissolving” in the mode that you describe. More like disintegrating for lack of maintenance as the end of spawning passed. But remember, apart from my general innocence of coelenterate taphonomy, I really have no personal knowledge of the Mediterranean, so I am just letting my thoughts flap in the breeze from my tongue (metaphorically of course; I am not typing aloud.)

>Also, when considering that something may have been nibbling away at them, remember that the nematocysts of which the tentacles are covered have the ability to remain functional, for a time, even after a jellyfish dies.<

Again, that would depend on the jellyfish’s biology. Spawning jellyfish of some species for all I know, might very well stop feeding and protecting themselves when spawning. Their nematocysts might have been defunct for weeks by then, to avoid killing too many gametes.  

>Nematocysts which, needless to say, are specially designed to paralyze or cause pain to any of the various small creatures that might eat the tentacles and not the bells of the jellyfish.<

Well, not just “any”! Remember the intriguing ability of some nudibranchs to eat the most vicious cnidarians, nematocysts and all, and even to pass those nematocysts to their own skin for defence!    

>Admittedly, the global warming tag that I slapped on there doesn't have much to do with my question other than for the fact that it is often blamed for the frequent and unheralded jellyfish blooms now occurring en masse throughout the world. Sorry for the run-on.<

No problem. Certain small-souled persons have from time to time suggested that I, even I, might do better to focus my run-ons more narrowly. Still, the substance of  that particular run-on might do better in another line of discussion if you have any active ideas on the subject, no?

Cheers,

Jon

Excuse me, apparantly it turns out that most jellyfish consist, corporeally, of about 95% water (though some sources claim for it to be as high as 98%), with the rest of what's in there being mostly just trace elements. And believe me, they dissolve rapidly; I once left a freshly dead jellyfish in the shower (I was a strange child), which within less than an hour's time left not a trace of itself to be found but a slightly viscous liquid and an astronomically rancorous stench. From this I deduce that, had the tentacles had enough time to dissolve, the rest of their bodies would have had time at the very least to be floating around in partial decay.

Also, when considering that something may have been nibbling away at them, remember that the nematocysts of which the tentacles are covered have the ability to remain functional, for a time, even after a jellyfish dies. Nematocysts which, needless to say, are specially designed to paralyze or cause pain to any of the various small creatures that might eat the tentacles and not the bells of the jellyfish.

Admittedly, the global warming tag that I slapped on there doesn't have much to do with my question other than for the fact that it is often blamed for the frequent and unheralded jellyfish blooms now occurring en masse throughout the world. Sorry for the run-on.  I therefore decided to include it as I thought this question might interest anybody searching for material related to the connection between global warming and the enormous pulsating phalanxes of jellyfish now popping up everywhere in the seas and oceans. That, and everyone and their mom seems to have global warming fever nowadays, so I figured more people would stumble upon it in their searches.

Remarkable experience, but I know little about jellyfish and less about the Mediterranean, so the only reason I bother to speculate is that no one else seems keen.

BTW, 97% seems a bit high to me for a marine organism, particularly in the Mediterranean; have you measured it? Let us know if you have any hard data on the point.

OK. My guess is that they had indeed just finished a spawning event and were dying. Consider. They appeared in massive concentrations, abruptly and in concert. They were generally in similar states of dissolution at about the same time. Other species in the same area seemed to be in working nick. That all seems to me to be consistent with a shoal that had assembled for spawning, done their best and worst, and signed off. No doubt it was not yet time for those other species.

Conceivably in releasing their spawn they had lost some of their reproductive appendages, and maybe some tentacles with them. Assuming that enough of my speculations so far are near the mark, we now have umpty thump moribund jellyfish drifting around all together in unsympathetic, agitated waters, for the benefits of eager scavengers and nonplussed swimmers. Now, which parts of the jellyfish would suffer first and worst? And which would break off fastest under the influence of decay? I would guess the most exposed and most delicate. Sounds like a fair diagnosis of frills and furbelows to me! Like tentacles in fact. I have on occasion found large, dead jellyfish, and commonly they had no residual tentacles to speak of.

I see that in one of the tags someone raised the question of global warming; the connection is unclear. Do current advances in dendrochronology suggest that hot tentacles have historically broken off faster than cool?

Running out of ideas in context, I am afraid. How am I doing?

Cheers,

Jon