The sea urchin sample comprises five remains: one hemipyramid, and four test plates (Table 2). Species identification is based on one test plate that is large enough to allow the diagnostic count of pore-pairs, indicating the presence of Paracentrotus lividus (Lamarck, 1816). All specimens come from the reworked parts of the deposit that contain Holocene intrusions.

Based on test remains (Figure 4A; no terga or scuta plates were recovered) 81.25% (NISP = 130) of the barnacle assemblage could be identified as Perforatus perforatus (Bruguière, 1789). About a quarter of the remains (38.13% or NISP = 61) come from the reworked deposit, but the great majority was found in the MIS 5 deposit; most are from Phase FB4, and a single remain is from Phase FB2 (Table 2).

With regards to crabs, a total of 809 remains were recovered and examined; more than half (or 56.7%) were identified to species (Tables 2, 3). The taxonomic identification was based on pincers (propodus and dactylopodus) and mandibles, allowing the identification of five different species. The assemblage from the MIS 5 deposit is overwhelmingly dominated by Cancer pagurus (Linnaeus, 1758; the brown crab), which is also represented in the reworked deposit, where most remains of this taxon feature the diagnostic concretion coating of the in situ material and therefore must correspond to Pleistocene-age finds. Conversely, Pachygrapsus marmoratus (Fabricius, 1787; the marbled rock crab) is absent from the in situ Pleistocene assemblage, despite being the dominant taxon amongst the non-concretion-coated crabs of the reworked deposit. Maja squinado (Herbst, 1788; the spider crab) occurs more frequently in the MIS 5 deposit than in the reworked deposit. A few non-concretion-coated remains of Eriphia verrucosa (Forsskål, 1775; the yellow crab) and Carcinus maenas (Linnaeus, 1758; the green crab) were found in the reworked deposit and, like P. marmoratus, must correspond to Holocene intrusions.

The remains from the reworked deposit tend to show less fragmentation when compared to those found in the in situ MIS 5 deposit. This is clear for barnacles, which, in the reworked deposit, are complete in 75.40% (NISP = 46) of the cases, as opposed to only 53.54% (NISP = 53) in the in situ MIS 5 deposit; their robust calcite tests explain the high degree of completeness seen in both cases. The sea urchin remains all show recent fractures.

Overall, crab remains are mostly fractured (90.98%; NISP = 736). However, it is notable that 67.5% (NISP = 27) of the P. marmoratus assemblage corresponds to complete or nearly complete claws, confirming good shell preservation in a species that is naturally fragile and prone to breakage. The opposite happens to the robust shell of Cancer pagurus, for which only 7.03% (or NISP = 26) of the claw remains are nearly complete (Tables 3, 4). The use of power tools to excavate the heavily brecciated parts of the deposit does not seem to have had much impact on the crab remains, since most show no excavation-induced breakage; most recent fractures were observed in the reworked deposit (NISP = 83; cf. NISP = 5 in the MIS 5 deposit). Finally, when broken, most crab claws identified to species present transversal fractures, except for Cancer pagurus, among which longitudinal fractures predominate and complete pincers are absent (Table 4). Longitudinal fractures are regularly found on the outer edge of the pincers of Cancer pagurus, i.e., on the edge opposite to the claw's protuberances (Figure 4D). However, whenever the propodus and the dactylopodus are identified based on the presence of their distal ends, fractures tend to be transverse. Both longitudinal and transverse fractures on Cancer pagurus claws are clean and smooth edged with a right angle.

Thermo-alterations were identified on two barnacle plate fragments, but were mostly found among the crab remains; none were seen in the sea urchin assemblage. In the crab assemblage, 8.41% (NISP = 68) of the remains are burnt (Table 5); black burns are the most frequent (Figure 4B), burning colors reflecting very high temperatures (gray and white) are nearly absent and, except for six carapace elements, it is the claws that are burnt, and almost exclusively Cancer pagurus ones. No burning was observed on remains of the taxa that only occur in the reworked deposit containing Holocene intrusions.

No surface modifications were observed on sea urchin remains. Half of the barnacle assemblage (51.3% or NISP = 82) shows calcareous coatings, but only two remains feature sediment fillings and another two have dissolution marks on their dorsal side. Abrasion and incrustation are absent. There is evidence of one perforation, but due to its size and shape, it is probably due to gastropod predation.

Crab remains do not feature incrustation or abrasion marks, the latter implying the lack of exposure to strong tide activity. Focusing on the MIS 5 remains, all show coating with calcareous concretions, 18.2% (or NISP = 122) have sediment fillings, and dissolution was detected on ten specimens. No carnivore or rodent gnawing marks were detected, and anthropogenic incisions are also absent. A total of ten impact scars were found on the ventral side of the proximal end of Cancer pagurus dactylopoda (Figure 4C).

Carapace width could be measured in two Carcinus maenas remains from the reworked deposit, revealing a population ranging in size between 53 and 73 mm. The in situ deposit is overwhelmingly dominated by Cancer pagurus, whose carapace width was estimated from the length of the pincers to range between 111 and 223 mm, averaging 162 mm (Figure 5).

Considering the scarce literature available for crustacean and echinoderm archaeological remains, most of the assumptions underpinning our identification of the agents of accumulation involved derive from criteria used in studies of other shellfish and small animal remains.

Natural accumulations are expected to show individuals in anatomical connection or in close association, with a relatively good state of preservation and low fragmentation (Bishop, 1986). As summarized by Erlandson and Moss (2001), several carnivores—e.g., canids, felids, bears, and otters—are opportunistic shellfish predators, and there are also several non-human primates that eat crabs (Russon et al., 2014; Koops et al., 2019). These animals can transport crabs to archaeological sites, and their participation in the accumulation can be inferred from the presence of their own skeletons and the identification of digestion, gnawing, and bite marks. A variety of birds can also be responsible for the accumulation of crab remains, e.g., cormorants, condors, sea eagles, corvids, and gulls. Such accumulations are often related with nesting and show high levels of fragmentation with random types of fracture, as those birds use gravity (dropping of the shellfish from high above onto rocks below) to break the shell open and expose the edible flesh (Erlandson and Moss, 2001).

An anthropogenic accumulation is expected to be found in stratigraphic association with stone tools and other features, such as hearths; to show surface modifications (like burning), patterns of mechanical fracture and, potentially, some cuts and percussion marks. Based on such criteria, Neanderthal mollusc accumulations have been identified in Gibraltar caves (Finlayson, 2008; Stringer et al., 2008), as well as in Bajondillo Cave, Spain (Córtez-Sánchez et al., 2011). Similar criteria have been used for the South African Middle Stone Age shellfish accumulations recovered from Sea Harvest (Volman, 1978), Hoedjiespunt (Will et al., 2013; Kyriacou et al., 2015), Klasies River (Thackeray, 1988; Langejans et al., 2012), Ysterfontein 1 (Klein et al., 2004), Pinnacle Point 13B (Marean et al., 2007; Jerardino and Marean, 2010) and Blombos Cave (Langejans et al., 2012). Moreover, an anthropogenic accumulation is expected to be size-selective, thus showing preference for larger animals with higher meat content.

At Gruta da Figueira Brava, two different agents seem to have been involved in the accumulation of the crab remains. The reworked deposit shows high species diversity and is whence all specimens of Pachygrapsus marmoratus and Eriphia verrucosa come; most Carcinus maenas remains were also recovered therein. Even though the remains of these species are fragile and prone to breakage, preservation tends to be good and there is a high degree of completeness; there are several complete pincers, and most fractures are recent, ruling out accumulation by carnivores, which would typically feature a high degree of fragmentation. The same applies to the fragile test fragments of sea urchins. We can therefore conclude that these remains were not significantly exposed to damage, either from the dynamics of sedimentary accumulation or from the impact of marine dynamics (e.g., shell abrasion, or incrustation by barnacles or parasites). Likely, the remains represent recent Holocene natural deaths, whether in the cave itself or in the adjacent rocky beach, that eventually made their way into the sedimentary fill via natural agency, namely burrowing by small mammals. Indeed, nowadays Pachygrapsus marmoratus is common in the intertidal pools around Gruta da Figueira Brava. As is also the case with Carcinus maenas and Eriphia verrucosa, these crabs move along the creeks and crevices of the rocks, and they inhabit seashore caves whose wet environment provides welcoming shelter (Ingle, 1996). Moreover, no carnivore marks were identified in any crustacean or urchin remains, and overall carnivore presence in the cave is scant (Zilhão et al., 2020).

With regards to the in situ deposit, which is dominated by Cancer pagurus, the crab remains bear no evidence of carnivore or raptor modification. Moreover, brown crabs were selected for large carapace width (on average, 160 mm), which reflects a preference for adult males weighing around 800 g (Woll, 2006; Haigh et al., 2015). Apart from humans, the other agents capable of transporting such large crabs over the distances involved—during Phase FB4, where 99% of Cancer pagurus and Maja squinado remains belong, the site-to-shore distance was ~2 km (Table 2; Zilhão et al., 2020)—are the aquatic eagle and other raptors of similar size (Erlandson and Moss, 2001). However, such birds do not nest in caves, and even less so when human occupation is frequent and regular. In the adult age indicated by the body size estimations, the brown crab can inhabit the low waters close to the shoreline and has a preference for living in the sea floor, which argues against the archaeological specimens representing predation by land-based animals, as does the estimated site-to-shore distance. Finally, the type of fracture observed on crab pincers, the fact that many remains are burnt, and the impact scars suggesting claw disarticulation further corroborate the anthropogenic nature of the accumulation of the MIS 5 crabs.

Archaeological crab remains are mostly identified by their pincers, which are the most diagnostic body parts. Unsurprisingly, all five crab species represented at Gruta da Figueira Brava were identified that way; however, the presence of diverse skeletal parts, even if some are poorly represented, bespeaks of the introduction of complete animals. Experimental work on the crab cuticles confirms that pincers are the body part most likely to preserve due to its low porosity (Plotnick et al., 1988; Mutel et al., 2008; Waugh et al., 2009). Krause et al. (2011) have also shown that pincers have a high calcium carbonate content and, hence, preserve better than the other parts of the exoskeleton.

The taxa identified at Figueira Brava can all be found in the Portuguese Atlantic coast, and they are all edible, even though some (e.g., Pachygrapsus marmoratus) are currently ignored due to their small size. All species are intertidal and can easily be found in low tide pools among algae, beach boulders, and rock creeks. However, large size adults of Cancer pagurus and Maja squinado are most commonly reported to be found in such locations only during the summer months (sometimes until October), when seawater warms up and the crabs migrate to the shore for reproduction. During the rest of the year, large size indivuals of these species remain confined to the subtidal zone (Ingle, 1996; Gruet, 2002; Woll, 2006).

Nowadays, several commercially important species of crabs are harvested using entrapment gear, like basket traps or pots, baited with herring, squid, or shad. Only sessile or slow-moving animals, like molluscs, gooseneck barnacles, and sea urchins are harvested by hand (Flick, 2012). Nonetheless, and despite the crabs' quick movement and escape strategies, there are several ethnographic examples of hand-collection from low tide pools, frequently aided by spears. The Nehalem Tillamook men of the northern Oregon Coast of America hunted crabs using long poles to stab them (Losey et al., 2004). This practice is also mentioned by von Brandt (1984) for coastal countries in Western Europe. Such a technique can be easily applied on shallow waters, as described by Swan (1972) for the Chinook of Willapa Bay in Washingston State (USA), who waded for crabs of large size in low tide pools. The Squamish people (Canada) are known to gather crabs from the beach in the summer (Conner and Bethune-Johnson, 1986). This is an activity described for women from several indigenous peoples from the Pacific Northwest Coast (e.g., the Haida, Murdock, 1963; the Kwakiutl, Wolcott, 1967; the Squamish, Conner and Bethune-Johnson, 1986); whereas men tend to be associated with crab hunting by spearing, as observed among the Makah (Renker and Gunther, 1990), the Eastern Abenaki speaking people (Snow, 1978), or the Wampanoag Indians of Massachusetts (Speck and Dexter, 1948). Batdorf (1990) notes that Dungeness crabs (from the Cancer genus) were hit by spears on the area behind the eyes, in order to daze the crab and to facilitate hand collection. The Cancer pagurus assemblage from Gruta da Figueira Brava shows clear selection for large size animals, which reflects individual hunting and not mass collection. Large individuals are easier to spot than smaller ones and, if crabs had been mass harvested, one would expect to find specimens of all sizes, as described by Losey et al. (2004) for the Oregon coast of America, which is not the case.

How crabs were processed can be inferred from the burning and breakage patterns. Even though most burning is found on the pincers, it can be seen on carapace fragments too (Figure 4B), further supporting the notion that complete animals were processed at the site. Ethnographic studies indicate that crabs are not consumed raw, and that they are commonly boiled, steamed or roasted (Suttles, 1974; Batdorf, 1990; Emmons, 1991). Boiling and steaming are not likely to result in the burning of crab remains, but roasting on the coals does leave thermo-alteration marks. At Gruta da Figueira Brava, the most common are black burns. Microstructurally, the exoskeleton of crabs, the bones of mammals, and the shells of molluscs are different, but the lessons garnered from the experimental work done on molluscs by Villagran (2014) and Milano et al. (2016) can nonetheless be used to interpret crustaceans. Based on such studies, black burns on crab shell reflect exposure to fire temperatures between 300 and 500°C (Villagran, 2014; Milano et al., 2016), which are generally accepted as typical for cooking (e.g., Pearce and Luff, 1994; Montón-Subías, 2002). Ethnography demonstrates that crab meat is considered to be cooked when it no longer sticks to the shell (Batdorf, 1990). Exposure to temperatures starting at 300°C results in dramatic changes in shell surface color, texture, and microstructure: shells become more fragile and easier to break (Milano et al., 2016), and, when processed, they will shatter because of their lower density (Rick et al., 2015). The flaking marks found on the ventral proximal side of dactylopoda suggest manual disarticulation. The predominance of longitudinal fractures on Cancer pagurus pincers bespeaks of the intention to access the flesh within the fingers, while the carapace was targeted for its large brown meat content (Table 6), as is the case today.

Cancer pagurus is one of the crustaceans mostly consumed in Southern Europe—Portugal, Spain, France, and Italy—during the summer holidays and over Christmas (Barrento et al., 2008). The marks seen on the archaeological material are very similar to those empirically produced when eating them today. The disarticulation of the claw fingers is done by manually breaking the joint backwards, which is sometimes aided by a small hammer. Such hammers, however, are most valuable for breaking the fingers themselves to access the white meat inside, which recurrently produces the same kinds of longitudinal fractures observed on the archaeological material.

Currently, crabs are seen as an important food resource, as they are considered to enhance good healthy living due to their high-quality and low-calorie protein, associated with a wide range of vitamins and minerals, but essentially due to the presence of long-chain polyunsaturated fatty acids (also known as PUFAs) including docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids (Tsape et al., 2010; Hicks, 2012; Ovat et al., 2018). Cancer pagurus, in particular, provides ample doses of elements such as potassium, calcium, copper, zinc, selenium, and PUFAs. Overall, brown meat (i.e., the tissue in the body cavity, mostly gonads and the hepatopancreas) contains higher fat, cadmium, calcium, iron, magnesium, and copper, whereas muscle (i.e., the white meat in the legs and claws) has a higher zinc content. Therefore, such crabs are among the seafoods with a higher potential to contribute to the improvement of cardiovascular and neurological aspects of human health (Maulvault et al., 2012).

Such nutritional properties are even more relevant if the crabs in question are adult Cancer pagurus, as is the case at Gruta da Figueira Brava, and they can be enhanced through culinary treatment. Crab cooking results in a decrease of the moisture content and EPA but in an increase in mineral, protein, carbohydrate, carbon, zinc, bromine, and chlorine content (Maulvault et al., 2012). Therefore, despite the low ranking of crabs in diet-breadth models due to their small size and apparent limited caloric intake (e.g., Winterhalder and Smith, 2000; Bird and O'Connell, 2006), they offer the benefit of nutrient diversity (Hockett and Haws, 2003, 2005) and are an appealing protein, fat and PUFA package easily acquired from the nearby shore, within minimal processing and transport efforts. In terms of meat yield, the selection for 800 g crabs would guarantee about 200 g of edible crab meat, since about 70% of the weight corresponds to the exoskeleton (Table 6)—i.e., in terms of edible meat, a single crab is the weight-equivalent of up to 250 limpet shells.

With regards to current seasonal crab availability, opinions diverge, as noted by Gutiérrez Zugasti et al. (2016). For instance, Brown and Bennett (1980) report that Cancer pagurus juveniles can remain in intertidal waters year-round and that adults are rare on the shore during the winter months, but Silva et al. (2014) report year-round presence with little variation in specimen density. This could be explained by the optimal conditions of food availability provided by upwelling, which, for Portuguese coast Cancer pagurus, results in an earlier breeding season (Cunha et al., 2018). Even though seasonality is, therefore, difficult to assess, it is clear that, in Phase FB4, crabs were consistently consumed throughout. Food is not only consumed for the satisfaction of nutritional needs, but also to experience esteemed flavors and to fulfill specific roles in social life. As demonstrated by ethnographic studies in Australia (Bailey, 1975; Meehan, 1977, 1983), resources that appear as minor in quantitative or nutritional terms may in fact be of significant importance in social, as well as, in subsistence terms. For the Middle Paleolithic, however, whether such foods were perceived as tasteful, reflected some sort of festivity, added social value to whoever harvested them, or had other consumption-associated meanings is beyond our grasp.