I got the Neanderthals on the Edge volume by interlibrary loan to follow up the Barton shellfish consumption reference. Here is the relevant passage from the discussion of that chapter:
Until recently any discussion of shellfish exploitation by Neanderthals or other archaic humans would have been restricted to just a few exceptional examples. However, following publication of work on the Italian Mousterian by Mary Stiner and others, there are now a growing number of instances where evidence has been documented for deliberate harvesting of marine shellfish resources by Neanderthals. These include cave sites and rockshelters in the Ligurian Riviera (Costa dei Balzi Rossi, Riparo Mochi, Barma Grande), further south in Latium (Grotta dei Moscerini) and in the southern Italian province of Puglia (Grotta dell'Alto, Grotta del Cavallo, Grotta Uluzzo C, Grotta Mario Bernadini, Grotta dei Giganti) (Stiner 1994, fig 6.9). Further afield in Africa similar occurrences have been reported from Middle Stone Age deposits at Blombos Cave in the southern Cape (Henshilwood and Sealy 1997) and at the Haua Fteah in Cyrenaica (Klein and Scott 1986). To these can now be added the localities of Vanguard and Gorham's Caves and the Devil's Tower, Gibraltar. The Gibraltar examples indicate that mussels and otehr shellfish probably contributed regularly to the Neanderthal diet. Furthermore they show that selective use was made of the larger shells collected from estuarine habitats and these small packages of food were carried up to four kilometres to the caves to be prepared and consumed. Much larger accumulations of shellfish in association with the Mousterian deposits are also known from unpublished sites north of Gibraltar near Torrelmolinos, in teh Spanish Costa del Sol (Miguel Cortés Sánchez pers. comm.).
The presence of thin in situ ashy hearth horizons in Vanguard Cave has helped establish that the use of the site by Neanderthals was generally episodic with individual occupation events usually being short-lived. Ephemeral use of this cave is exemplified by the upper hearth and midden which probably represented a single episode of use of no more than a few hours duration. Further down the sequence more intensive evidence of occupation is indicated by accumulations of butchered bones of ibex and red deer but here too the data are consistent with short-term occupational use. In both the upper and middle section of this cave it was noticeable that te hearths were positioned in proximity of hte soutehrn cave wall. Similar juxtapositions have been noted at other Mousterian sites (e.g. Tor Faraj, south Jordan; Henry 1998), but unlike Tor Faraj there is no suggestion of multiple individually spaced hearths. Indeed it is noreworthy that the single hearth in the middle section of Vanguard was re-used at least three times. This may reflect the generally lower density of human groups occupying the site at one time. The position of the hearths near the cave wall and the extensive ash spread in the upper part of the cave may also have been partly connected with sleeping or resting activities. For example in ethnographic contexts, it has been noted that ashy spreads between the hearth and the rock wall may coincide with places where bedding was laid down (Parkington and Mills 1991) (Barton 2000:218-219).
McBrearty and Brooks (2000:511-512) give a long list of MSA and associated sites with shellfish remains (taken broadly to include land snails and tortoises). This is a very long passage, and so I won't quote it, except for the conclusion:
Evidence from coastal Italy (Stiner, 1993, 1994; Stiner et al. 1999) and Gibraltar (Barton et al., 1999) shows that Neanderthals did sometimes eat marine shellfish, but the impressive escargotière at Mumba [Rock Shelter, Tanzania] and the numbers of coastal African sites containing quantities of shellfish seem to indicate a more regular intensive use of small scale resources in the MSA (McBrearty and Brooks 2000:512).
This is certainly one of those where I wouldn't want to have to be the graduate student to test that assertion -- after all, how many coastal Neandertal sites are there? And the occurrence of a unique site where land snails were intensively exploited doesn't seem like the best evidence. Notice how Barton described the relatively nonintensive occupation of the Gibraltar Mousterian caves. It would take some pretty sophisticated sampling to work out whether Neandertals and MSA Africans were significantly different in use of these resources.
Common sense suggests they wouldn't be, at least not without some reason. After all, the other protein-rich foods they had available were vastly more dangerous and risky to acquire. Finding shellfish at coastal sites would seem more like filling an obvious archaeological blind spot than saying something distinctive about resource collection abilities.
But then, the use of shellfish in particular figures into the "coastal dispersal" hypothesis for out-of-Africa. The idea that archaic humans were incapable of exploiting coastal resources is inconsistent with the data. But Paul Mellars (2006) presents a curious alternative view:
The second major factor in stone tool technology lies in the specific functions for which the tools were required. If, as most of the current models suggest, the initial colonization of southeastern Asia and Australasia followed a primarily coastal route (12, 18, 20, 21, 61), then the technologies would be likely to adapt primarily to the exploitation of coastal resources, such as fish, shellfish, and marine mammals (together with tropical plant foods) with perhaps only a minor component of hunting larger land mammals, of the kind that clearly formed a major part of the human economy in both Africa and the whole of western Asia and Europe (21, 59). This would presumably have involved much less emphasis on various forms of hunting equipment (such as spears, meat-processing tools, etc.), as well as equipment involved in the manufacture of elaborate skin clothing, or the construction of tents and other living structures, that were essential to survival in much colder, more northerly environments (59, 62).
In other words, Mellars proposes that southeast Asia and Australasia lost stone tool complexity that would have been present in their African ancestors, because they didn't eat many large land mammals.
This takes shellfish-dependence full circle -- hunters that once took African big game found instead that they could live the easy life following the coast and eating marine resources. Well, maybe -- it still seems like a lot of arm-waving based on distributions that may not be different from each other in any real way.
Barton N. 2000. Mousterian hearths and shellfish: late Neanderthal activities on Gibraltar. In Stringer CB, Barton RNE, Finlayson JC, eds., Neanderthals on the Edge: Papers from a conference marking the 150th anniversary of the Forbes' Quarry discovery, Gibraltar. Oxbow Books, Oxford. pp. 211-220.
McBrearty S, Brooks AS. 2000. The revolution that wasn't: a new interpretation of the origin of modern human behavior. J Hum Evol 39:453-563.
Mellars P. 2006. Going East: new genetic and archaeological perspectives on the modern human colonization of Eurasia. Science 313:796-800. DOI link