The spatiotemporal changes in fish and invertebrate community structure and habitat viability in the Yangtze Estuary

Temperature and oxygen are fundamental environmental factors shaping community structure and are major climatic stressors for marine species globally, interacting with physiological traits of species to establish marine habitats. Periodic seasonal fluctuations in temperature and oxygen significantly influence the composition of community structures and biogeographic habitat viability. This study utilized two community-based indices, the Aerobic Growth Index of the Community (AGIC) and the Mean Oxygen Demand of the Community (MODC), to understand the roles of temperature and oxygen in shaping the community structure of benthic fish and invertebrates during the spring and autumn in the Yangtze Estuary and quantified habitat viability across different seasonal and spatial regions. We observed pronounced seasonal differences in the environmental and community structures of the Yangtze Estuary, though variations in habitat viability across seasons were minimal. Autumn communities demonstrated lower vulnerability and higher resilience to hypoxia. Despite this, from 2004 to 2022, the annual fluctuations in temperature, oxygen levels, and habitat viability were minimal, maintaining high levels overall, except in the spring of 2004. Additionally, influenced by the Taiwan Warm Current, the southern region of the Yangtze Estuary exhibited lower habitat viability compared to the northern region. Although AGIC and MODC, as two new ecological indicators, are limited by some uncertainties, it can still provide guidance for future conservation of estuarine ecosystems and sustainable utilization of fishery resources under the ongoing global oxygen crisis.