Interdecadal variability in ecosystem health of Changjiang (Yangtze) River estuary using estuarine biotic integrity index

Ichthyoplankton samples were collected from Changjiang (Yangtze) River estuary in May 2016. Species composition was studied by DNA barcoding and morphological identification. To make better use of the estuarine biotic integrity index (EBI) to assess the ecosystem health of the Changjiang River estuary over the past 30 years, we collected the data of a spring ichthyoplankton survey in the estuary from 1986 to 2016. The EBI was calculated using 12 evaluation metrics, namely, the number of total ichthyoplankton species, estuarine spawning species, estuarine nursery species, estuarine resident species, benthic species, pelagic species, and intolerant species, and the percentages of tolerant species, omnivores, insectivores, carnivores, and natural hybrid species. EBI was calculated in spring in four periods (1986, 1999, 2007, and 2016) by assigning points of 1, 3 or 5, giving values of 50, 38, 36, and 32, respectively, corresponding to “Good”, “Fair-Poor”, “Fair-Poor”, and “Poor” EBI levels, respectively. Changes in species composition were the primary reason for the significant decreases in EBI between 1986 and 1999, and for the large differences between 1986 and 2007 and between 2007 and 2016. The changes in species composition were influenced by declines in ichthyoplankton species, pollution sensitive species, estuarine nursery species and estuarine sedentary species, and an increase in pollution resistant species. An analysis of EBI interdecadal variability showed that the health status of the Changjiang River estuary ecosystem over the last 30 years first declined and then stabilized at a lower level. This result further settled the argument for urgent protection and restoration of the Changjiang River estuary.