Projected impacts of ocean warming on pelagic ecosystems in the Western and Central Pacific Ocean using a multi-species size-spectrum model.

Ocean warming may alter food web structure and species interactions in pelagic ecosystems, significantly impacting tuna population dynamics. However, few studies have assessed those impacts from the perspective of species interaction and ecosystems. In this study, we developed a multi-species size-spectrum model (MSSM) incorporating Chinese longline fisheries data and public datasets to assess ocean warming effects on the Western and Central Pacific Ocean (WCPO) ecosystem under four climate scenarios (SSP1-2.6, SSP2-4.5, SSP3-7.0, SSP5-8.5). Our results demonstrate that ocean warming will affect natural mortality, mean body weight, and biomass and production of large pelagic species, including tunas, billfishes, and sharks in the WCPO. We found that ocean warming had greater impacts on billfishes and sharks growth and reproduction than on tunas, with Shortbill spearfish showing the most severe declines: >5 % in growth energy rates and > 7.5 % in reproduction energy rates under SSP5-8.5 versus SSP1-2.6 by 2100. The prediction results show that ocean warming has a greater impact on the natural mortality rate of some shark species than other species. By the end of the 21st century (2100), the natural mortality rate of Blue shark and Oceanic whitetip shark will increase by 8 % under the SSP5-8.5 scenario compared with the SSP1-2.6 scenario. Overall, ocean warming will cause changes in the structure of the WCPO pelagic ecosystem. The study offers scientific support for developing sustainable tuna fisheries and implementing climate-adaptive management strategies in response to future climate change.