Isotopic comparison of Roman time and modern fish species in Mallorca

Abstract

[eng] Human activities have significantly impacted Earth's ecosystems, leading to habitat changes and species extinctions. Human civilization has historical and evolutionary links to the ocean which has served as a vital source of essential biomolecules, sustenance and a key space for transport and commerce. However, overfishing, pollution, and other stressors have dramatically altered marine ecosystems globally. The Mediterranean is home to over 7% of global marine biodiversity and has been overexploited for over 2000 years and, therefore, it is facing severe degradation aggravated due to its semi-enclosed nature and high population density. Stable isotopes provide crucial insights into trophic pathways and feeding interactions in aquatic ecosystems. Analysing carbon (δ13C) and nitrogen (δ15N) isotopic signatures in tissues helps to determine the organisms' position in the food web. This study aims to assess the impact of human settlements over time on marine environments through stable isotope analyses on archaeological and modern fishbones. Mandibular and premaxillary bones from Sparus aurata, Pagrus pagrus, Pagellus erythrinus, Pagellus genus, Labrus genus and Diplodus genus were collected. Archaeological bones were obtained from the Roman port city of Pollentia, while modern samples were fished at the Bays of Palma and Alcúdia. All bones went through a collagen extraction protocol for the subsequent δ13C and δ15N stable isotope analysis. Additionally, regression models were employed to estimate the Standard Length (SL) of archaeological specimens. Statistical analysis, performed using R, aimed to uncover isotopic variations across species and time periods showed that, despite the C:N ratio suggesting that the collagen quality of the samples does not meet standard thresholds, our results show a clear trend, as all archaeological samples showed enriched δ13C and δ15N mean values compared to modern samples. Moreover, archaeological samples exhibit a notable dispersion with very distinct isotopic outcomes when compared to modern ones. In addition, archaeological species are considerably larger than modern ones.