Rise and fall of sambaquis in Babitonga Bay
Our review of radiocarbon dates for coastal sites in the AFPB reaffirms that the bulk of sambaquis activities occurred predominantly between ca. 5500 and 2000 years ago, followed by a steady decline of dated sites and a more dramatic abandonment of several sites from ca. 2200 years ago. This pattern has been observed and discussed in detail for lagoonal systems in the south of Santa Catarina state 27,46 and here we show that it extends to Babitonga Bay and to other areas of the AFPB. We concur with others that this process may have been triggered by a combination of environmental and social drivers, involving substantial reorganization of coastal environments and key ecological niches, with an unprecedented cascade effect on the local carrying capacity and the long-standing social, political and ideological systems developed around large ceremonial sites.
Pollen, sedimentary, and geochemical data show significant changes in coastal and marine ecosystems in Babitonga Bay and adjacent coastal areas from ca. 2000 years ago due to a combination of coastal regression, increasing precipitation and intensification of cold fronts in the Late Holocene 56,67−69. The decrease in relative sea level from the Middle-Late Holocene (+ 2.6 m) to a lower elevation (+ 1 m) at ca. 1000 cal BP 45 contributed to the progressive expansion of drylands and mangrove systems, potentially affecting spatial distribution and access to key resources (banks of intertidal and subtidal molluscs, fishing grounds, edible plants), as proposed for other regions 15,21,70. The silting-up of the estuarine-lagoonal water bodies and the consequent loss of intercommunication between these systems would have certainly impacted the carrying capacity of ecological niches that had maintained large community-based sites for centuries prior. The downtrend of dated sites suggests a gradual abandonment of sambaquis from around 2500 cal BP, culminating in their sharp abandonment ca. 2200 cal BP. This event possibly represents a turning point in the community-based nature of large ceremonial sites, which would have become unsustainable in most areas. As a result, several nucleated groups would have dissolved into smaller, dispersed and relatively independent social units organized in short-lived residential and logistic settlements that are notoriously less visible archaeologically. Although the radiocarbon dataset may be affected by a combination of taphonomic (e.g. site visibility and preservation) and research biases (e.g. more dates from non-ceramic sites), this population model would be supported by the increasing number of smaller and shallower sites along the coast of Santa Catarina state from ca. 2000 years ago 16–19,25−29.
As a result of this process, population density may have declined in several coastal areas, creating a new scenario of socio-cultural transformations and interactions with external groups 28,46. To date, genetic, osteological and archaeological data do not support the idea of population replacement with the introduction of ceramic technology to the coast from ca. 1200 cal BP. Rather, the increasing presence of ceramic artefacts and evidence of population admixture reveal variable degrees of interaction between sambaquis and cultural groups from the highlands 28,30,44,71−73. The exact nature of these interactions is still a matter of debate, but it certainly involved the circulation of people, artefacts, ideas and worldviews.
Fishing intensification
Our review of the stable carbon and nitrogen isotope composition of nearly 200 human individuals from non-ceramic coastal sites reaffirms the central role of marine resources in sustaining populations along the southern Atlantic Forest coast of Brazil during the Late Holocene. The newly generated faunal baseline for pre-Columbian sites in Babitonga Bay, coupled with BSIMMs, indicate that the exploitation of marine-brackish resources provided the majority of dietary protein to coastal groups before and after the introduction of ceramic technology, being a fundamental subsistence strategy to enhance resilience during climate, environmental and social instability in the Late Holocene. Plants supplied the majority of dietary calories, as documented by other lines of evidence 41,43,47, and their importance to diet may have led to some local intensification 31. Interestingly, individuals with mixed marine and C3 terrestrial diets or with diets dominated by terrestrial resources from C3 ecosystems were mostly found among Middle-Late Holocene populations (e.g. Morro do Ouro, Rio Comprido), while an increased reliance on marine-brackish organisms appears to have occurred mostly during the Late Holocene. Crouch et al. 40 analyzed the δ13C and δ15N values of several human individuals from the southern coast of Brazil and detected a significant increase in marine resource consumption with the introduction of ceramics. Our results suggest this trend may have been initiated prior to this introduction, and rather continued during the widespread adoption of ceramics, even though the number of individuals from some sites are too low (e.g. Casa de Pedra, Enseada I and Espinheiro II) to draw conclusive interpretations based only on stable isotopes.
The adoption of ceramic technology from ca. 1200 years ago corresponds with zooarchaeological evidence of intensification of fishing practices. Studies have shown that Late Holocene groups, and notably those using Taquara-Itararé ceramics, were fishing and hunting up the marine food web. Sharks were commonly targeted by some of these groups and, due to their individual biomass, they may have made a much higher contribution to diet than previously considered 74,75. For example, at Enseada I, fish become relatively more abundant in ceramic contexts (48%) compared to non-ceramic levels (32.4%), and involved the capture of high trophic level species (Trichiurus lepturus, Lagocephalus laevigatus, Carcharias taurus) 76. At Forte Marechal Luz, deposits prior to and after the adoption of ceramics contained large amounts of sea mammal, bird, reptile, and fish remains, the latter including sharks and rays 58. Moving south, remains of top predators such as fur seals (Arctocephalus australis), dolphins (Delphinus delphis, Tursiops truncatus) and sharks (Carcharias taurus, Carcharodon carcharias, Galeocerdo cuvier), among others, were found in ceramic deposits of Praia das Laranjeiras II (Camboriú) 77. At the ceramic site of Rio do Meio (Florianópolis), a large variety of fish, including a remarkable diversity of sharks (Carcharhinus plumbeus, C. obscurus, C. leucas, C. brachyurus, Rhizoprionodon sp., Carcharodon carcharias, etc.) were exploited 74,75,78. A very similar faunal record was documented for the ceramic site of Tapera, also in Florianópolis, which included sharks (Odontaspis, Prionace glauca, Galeocerdo cuvier) and sea mammals (Otariidae, Tursiops truncatus) 79. Further south, ceramic using groups in Galheta IV (Laguna) targeted a range of sea mammals (Otariidae), sharks (e.g. Carcharias taurus, Carcharodon carcharias, Sphyrna sp., Prionace sp.), rays (Dasyatidae, Rhinoptera sp.) and sea birds (Thalassarche sp.) 80.
Human osteological records provide evidence for increasing interpersonal violence among these later populations 29,81,82, possibly in a context of competition for resources and increased territoriality 83,84. This may have prompted technological innovation or adoption, represented by the appearance of baited hooks manufactured from mammal bones in Babitonga Bay and adjacent coastal areas from ca. 1200 years ago 58,77,85. Mostly found in contexts with ceramic artefacts (i.e. in Itacoara, Enseada I, Forte Marechal Luz, but also Laranjeiras II, Rio do Meio and potentially Cabeçudas in the north of Santa Catarina state 19,58,77), these hooks reflect attempts to increase fishing efficiency and expand fishing to new ecological niches. Baited hooks are not contingent upon the visibility of the target, and thus are an ideal implement for expanding fishing capabilities to deeper waters, including offshore habitats. Conceivably, other fishing hooks partially composed of bone and perishable materials (wood) may have been used in early times, as suggested by numerous bone points in sambaqui sites 11, but their functional interpretation remains a matter of debate. The importance of aquatic resources is also reflected in the use of ceramic artefacts, as revealed by residues of aquatic organisms in Taquara-Itararé pots from coastal sites 30,86−88. While we recognize that demographic trends and dietary estimates can be further refined with increasing radiocarbon dates and stable isotope analysis of faunal and plant baselines, the results presented herein reinforce the central role of coastal resources to significant cultural and demographic processes in pre-Columbian South America. Coastal adapted populations of the Atlantic Forest are examples of how fishing intensification was a possible outcome of environmental and social instability during the Late Holocene.