The Potential of Benthic Foraminifera Carbon and Oxygen Isotopic Proxies as Environmental Indicators in Coral Reef Regions

Abstract Using reef‐dwelling benthic foraminifera for paleoenvironmental reconstruction remains an unresolved challenge. Therefore, to evaluate the efficacy of using the δ 18 O and δ 13 C values obtained from benthic foraminifera species as environmental indicators in tropical reef regions, 233 specimens of 20 species collected from Huangyan Island and Lingyang Reef in the South China Sea were studied. The analyzed foraminifera species exhibited significant inter‐ and intraspecific variations for both δ 18 O and δ 13 C values, with δ 13 C values displaying greater overall intraspecific variability. Clear distinctions were observed between the symbiont‐bearing large benthic foraminifera (LBF) and symbiont‐barren small benthic foraminifera, with the latter displaying slight oscillations around the isotopic values of the estimated equilibrium calcite and the δ 18 O and δ 13 C values of the LBF miliolids and rotaliids exhibiting markedly divergent trends. Miliolids generally showed higher isotopic values than equilibrium calcite, while rotaliids exhibited lower values, which may be attributed to variations in the calcification patterns and symbiotic algae associations. The δ 18 O and δ 13 C values of two LBF species at the two studied sites are generally consistent with the sea surface temperature and productivity levels, providing valuable insight into the utilization of reef‐dwelling foraminifera as environmental indicators. The results of this study support the hypothesis that the δ 18 O and δ 13 C values of certain reef‐dwelling foraminifera are reliable environmental indicators and offer valuable insights for paleoenvironmental reconstruction and marine ecosystem forecasting, although the limitations of this method should be considered in practical applications.