Uncovering foraminiferal assemblages in Pulau Redang and the importance of FoRAM index calibration for reef monitoring in South China sea

Abstract

To mitigate adverse effects of ocean warming on coral reef degradation, resource managers increasingly explore management and regulation of local stressors to strengthen coral resilience and recovery. Comprehensive assessments and monitoring efforts offer a holistic understanding of reef dynamic ecosystems. In this study, we documented the distribution of benthic foraminiferal assemblages surrounding Pulau Redang, Malaysia, and assessed their potential for monitoring coral reef health using the Foraminifera in Reef Assessment and Monitoring (FoRAM) Index. Undeveloped (R1–R3) and developed (R4–R6) reef sites revealed distinct differences in reef conditions. Foraminiferal distribution showed Amphistegina lessonii (14–34%) as the dominant species, followed by Calcarina hispida (21%) and Calcarina mayori (19%). The Q-mode cluster analysis classified the distribution of foraminiferal assemblages in Pulau Redang into four sub-groups based on the reef ecological conditions. Group A1 and A2, represent the foraminiferal assemblage on the undeveloped west side of the island where live coral cover was >30%. Meanwhile, Group B1 and B2 represent the assemblage found in developed coastal regions with low live coral cover (≤20%). Additionally, the CCA results revealed a substantial influence of substrate type on the distribution of benthic foraminifera in the reef environments of Pulau Redang. FoRAM index consistently yielded high values across the study area despite varying coral reef conditions, probably due to the prevalence of Calcarina mayori in mesotrophic reefs (R4–R6), potentially distorting FoRAM values and providing a misleading indicator of reef conditions. The Modified Foram Index (MFI), calculated by excluding calcarinids, classified R3, R4, and R6 as less conducive for reef growth, aligning better with observed reef conditions. We recommend calibrating the FoRAM Index, particularly in mesotrophic reefs where calcarinids dominate foraminiferal assemblages, to enhance its precision and reliability for coral reef health monitoring and assessment within the region.