Climate change projections show shrinking deep-water ecosystems with implications for biodiversity and aquaculture in the Northwest Pacific.

The increased availability of environmental data with depth deriving from remote-sensing-based datasets permits more comprehensive modelling of the distribution of marine ecosystems in space and time. This research tests the potential of such objective modelling of marine ecosystems in four dimensions, spatial and temporal, to provide projections of how climate change may affect biodiversity, including aquaculture. This approach could be replicated for any regional seas. The Bohai Sea, Yellow Sea, and East China Sea (BYECS) are marginal seas in the Northwest Pacific bounded by China, Korea, and Japan. Despite providing important ecological and economic services, their ecological conditions and ecosystems distribution have not yet been systematically mapped. This analysis used 13 marine environmental variables, measured on a three-dimensional and monthly basis during 1993-2019, to classify and map the BYECS region by k-means clustering using cosine similarity as distance function. There were 13 distinct areas identified that fit the definition of "ecosystems" that is, enduring regions demarcated by environmental characteristics. Of these 13 ecosystems, the Yellow Sea Cold Water (YSCW) Ecosystem is significant in relation to seasonal species composition and the newly developing deep-sea salmon caging aquaculture in the region. Projections of the potential size of this water mass under various climate-change scenarios based on analysis using the Non-Parametric Probabilistic Ecological Niche (NPPEN) model show that its volume may decrease 31 %-66 % in the future. Such a decrease would have impacts on the seasonal species' abundances in the BYECS marginal sea region and threaten the deep-sea cold-water salmon farming.