Potential ‘origin’ areas of marine surface organisms in the Indo-Pacific convergence zone inferred from current-driven particle-backtracking simulations

The Indo-Pacific Convergence Zone (IPCZ) is an important center of global marine biodiversity. However, the origins of marine species in the IPCZ remain unclear. Understanding the origin areas of marine surface organisms in the IPCZ is critical for developing ocean conservation strategies and designing marine protected areas. Particle-backtracking simulation, as an essential numerical tracking technique, can reveal the sources of objects by tracing their dispersal pathways. In this study, numerical particle-backtracking simulations initialized at different dates using the ocean currents from an ocean circulation model with data assimilation were carried out to infer the potential ‘origin’ areas of IPCZ marine surface organisms. The resulting distribution of particle trajectories indicates that coastal areas are potential sites of origin or spawning grounds for some marine surface organisms. Specially, the IPCZ coastal regions may harbor IPCZ and peripheral Eastern Indian Ocean organisms, whereas the Eastern Pacific coastal zones potentially sustain peripheral Western Pacific organisms. The newly defined terrestrial intensity (TI) confirms that the IPCZ exhibits a higher proportion of organisms with a coastal ‘origin’ than the peripheral regions. Additionally, variations in initial ocean currents have no significant influences on TI in the IPCZ yet cause some differences in peripheral areas, potentially due to ocean currents driven by monsoons or other events characterized by interannual variability. • Possible “origins” of IPCZ marine organisms are inferred via particle backtracking. • The coastal regions are potential origin sites or spawning grounds. • IPCZ coastal regions may harbor IPCZ and peripheral Eastern Indian Ocean organisms. • Eastern Pacific coastal zones potentially sustain peripheral WP organisms. • Ocean currents play important roles in transporting particles.