Niche comparison and range shifts for two Kappaphycus species in the Indo-Pacific Ocean under climate change

Nowadays, eucheumatoids lead the rankings in globally cultivated seaweed production, including the seaweeds Kappaphycus alvarezii and Kappaphycus striatus. Eucheumatoids have declined in biomass over recent years, and climate change is regarded as one of the important factors. Thus, it is urgent to investigate the range dynamics of Kappaphycus under climate change. Considering its high practical relevance for conserving biodiversity, the niche conservatism hypothesis was tested between the two species through ecological niche modeling (ENM), ordination, and hypervolume approach which quantify the extent of niche overlap. In this study, we sifted the best performing algorithm Maxent and tuned parameters for fitting the distribution of both Kappaphycus species, compared their geographical distribution patterns, and predicted their range dynamics under climate change. All three methodological approaches indicated significant niche differences in both geographical and environmental space between the two Kappaphycus species. Our models predicted that range shifts mainly induced by rising sea surface temperature are likely to differ between two Kappaphycus species, with K. striatus suffering much range contraction (359,448 km2 in 2100s RCP8.5). By the year 2100, both Kappaphycus species are forecast to lose suitable habitats along most of the coastline of Southeast Asia under the RCP8.5 scenario. K. alvarezii is predicted to expand its distributions (96,429 km2) under the RCP2.6 scenario by the year 2100, suggesting resilience to mild global warming. Our study enhances the understanding of Kappaphycus aquaculture, and is conducive to the sustainable development of tropical seaweed by stressing the importance of conservation and investigation under climate change.