Poleward migration of tropical corals inhibited by future trends of seawater temperature and calcium carbonate (CaCO3) saturation

• Published in: The Science of the total environment 2024-06, Vol.929, p.172562-172562, Article 172562
• Main Authors: Huang, Ya-Yi, Chen, Ting-Ru, Lai, Kim Phuong, Kuo, Chao-Yang, Ho, Ming-Jay, Hsieh, Hernyi Justin, Hsin, Yi-Chia, Chen, Chaolun A.
• Format: Article
• Language: English
• Subjects: Global climate change; Non-reefal coral community; Omega aragonite; Omega calcite; Pocillopora; Poleward migration; Species distribution modeling; SST
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2024.172562

Poleward range expansion of marine organisms is commonly attributed to anthropogenic ocean warming. However, the extent to which a single species can migrate poleward remains unclear. In this study, we used molecular data to examine the current distribution of the Pocillopora damicornis species complex in Taiwan waters and applied niche modeling to predict its potential range through the end of the 21st Century. The P. damicornis species complex is widespread across shallow, tropical and subtropical waters of the Indo-Pacific regions. Our results revealed that populations from subtropical nonreefal coral communities are P. damicornis, whose native geographical ranges are approximately between 23°N and 35°N. In contrast, those from tropical reefs are P. acuta. Our analysis of 50 environmental data layers demonstrated that the concentrations of CaCO3 polymorphs had the greatest contributions to the distributions of the two species. Future projections under intermediate shared socioeconomic pathways (SSP) 2–4.5 and very high (SSP5–8.5) scenarios of greenhouse gas emissions showed that while sea surface temperature (SST) isotherms would shift northwards, saturation isolines of two CaCO3 polymorphs, calcite (Ωcal) and aragonite (Ωarag), would shift southwards by 2100. Subsequent predictions of future suitable habitats under those conditions indicated that distinct delimitation of geographical ranges for the two species would persist, and neither would extend beyond its native geographical zones, indicating that tropical Taiwan waters are the northern limit for P. acuta. In contrast, subtropical waters are the southern limit for P. damicornis. We concluded that the decline in CaCO3 saturation would make high latitudes less inhabitable, which could be one of the boundary elements that limit poleward range expansion driven by rising SSTs and preserve the latitudinal diversity gradient (LDG) on Earth. Consequently, poleward migration of tropical reef corals to cope with warming oceans should be reevaluated. [Display omitted] •Species range expansion is constrained by geological time and evolutionary pace.•Poleward migration of tropical species is challenged by molecular evidence.•Populations of similar morphology in two geographical zones are distinct species.•Range fluctuations would only occur within species' native geographic zone by 2100.•Tropical corals migrate poleward to cope with rising SST should be re-evaluated.