Pica 8 is a Late Intermediate Period (AD 900–1450) cemetery located in the Atacama Desert. Burials at the site present unexpectedly high variability in δ13C (–8‰ to –16‰) and δ15N (10‰ to 24‰) values in their skeletal tissues, implying highly diverse diets. There are two possible explanations for this variability: the first is diachronic change in diet while the second involves synchronic sociocultural distinctions. To distinguish between them a radiocarbon (14C) dating program (n=23) was initiated. The presumed importance of marine foods adds the complication of a marine reservoir effect. To address this problem, paired 14C dates were obtained on human bone and camelid textiles from nine graves. The results fall into two groups, one showing an average offset of 117±9 14C yr, and the other no statistically significant offsets. We conclude that the contribution of marine foods to bone collagen at Pica 8 was less than previously supposed. Other factors must be invoked to account for the unusually high human δ15N values at the site. Manuring crops with sea-bird guano emerges as a probable explanation. No relationship with chronology is seen implying the presence of considerable diversity in diets and hence lifeways within the Pica 8 community.

Dual stable isotope analyses (δ13C and δ15N) of fiddler crabs from a forest-fringed, land-locked lagoon in Puerto Rico indicated the differential assimilation of material from ingested sediments. Fiddler crabs preferentially selected for nitrogen-fixing benthic microalgae (cyanobacteria) over vascular plant detritus. These results question the assumption that mangrove detritus is always the principal source of energy to estuarine consumers. Previous research from this lagoon as well as from Amazonia suggests that the magnitude of land-water ecotonal coupling may be low for these particular tropical systems where benthic algal productivity is presumably high.