# Environmental Changes and Cultural Transitions in SW Iberia during the Early-Mid Holocene
## 4 Discussion
### Human Groups in Dynamic Littoral Habitats
An example would be the development of the complex shell-midden basecamps located in inland areas following the course of the Tejo and Sado Rivers, as opposed to the seasonal shell-middens located in the Algarve coast. This change of settlement patterns is explained as the result of a decline in the availability of the marine resources due to the joint action of a drop in the upwelling intensity together with an increased aridity _ca._ 8.2 ka BP [116]. This would have made the palaeoestuaries of these rivers stable resource-rich brackish environments, unlike the coastal unstable ecosystems adversely affected by this episode [116]. Likewise, results from the Pena d'Agua rock-shelter show important changes in the acquisition of raw material and technological features, which would be explained by modifications in mobility patterns from residential to logistic as an adaptive response to changing environments from 8.2 ka BP onwards [117]. Considering this hypothesis, these changes may have accelerated the confluence of human groups to settle in areas with stable and available resources, resulting in a (semi)sedentary pattern and social complexity [116; 117; 118]. However, there is no sign of the impact of the 8.2 ka BP event in the SW Atlantic Iberian margin in terms of settlement patterns. Notwithstanding, the bias caused by the lack of information needs more research in the study area to discern whether the seasonality of these sites reflect important regional differences, or if it is related to the existence of some (semi)permanent undiscovered basecamps. Regarding the diet, not only shell-middens from Western Algarve display a specialization in the exploitation of marine resources, but also the seasonal occupation of Palmones revealed an intense gathering of shellfish [15]. Isotopic analysis of the Vale Boi teeth showed that, although marine resources were a prominent element, the diet of these Mesolithic groups was based on a mix of terrestrial and aquatic resources [12]. However, there may have been important differences between sites, because isotopic data from the Sado shell-middens corroborated frequencies of marine diet _ca._ 25% [119], while in the Muge area the marine diet is above 50% [120]. In the occidental area of the Algarve, topshells were the most abundant species consumed during the Early Mesolithic, while limpets and gooseneck barnacles were preferred during the Late Mesolithic and Early Neolithic [121]. A reduction in the size of the shellfish collected was also identified in the transition from Mesolithic to Neolithic at Vale Boi, Rocha das Gaivotas, and Armacao Nova, and it was considered a consequence of overexploitation [12] or a decrease in the foraging efficiency [121]. However, in some Mediterranean areas such as the Pego palaeogoon, a reduction of lagoon bivalve size during the Late Mesolithic has been observed, related to a decrease in resource productivity [122]. Despite this there was gently increase in ocean organic productivity linked to the slow overall cooling of the waters during the Mid Holocene, the warmer climate during the Holocene Thermal Maximum caused a weakening of the coastal upwelling, briefly interrupted during the short cooling episodes [79]. This alteration in the coastal palaeoproductivity suggests that the modification in consumption patterns and the size decrease of shellfish in SW Iberian sites may have been a consequence of these environmental alterations rather than being caused by cultural factors. Commonly, the expansion of the Neolithic in both the western and eastern sectors of the Gulf of Cadiz is considered to have occurred around 7.5 ka BP [9; 12]. Corresponding to the period, different sequences reflect an aridity crisis affecting the vegetation of the SW Atlantic Iberian coast and the Alboran Sea [91; 101; 102; 103; 106; 107; 109] and the geochemistry dataset reflects a decrease of land moisture (Figure 6e).