Rapid habitat fragmentation and niche shifting of an estuarine dolphin driven by coastal urbanization

Abstract

Estuaries are critical habitats for many marine species, but are also experiencing rapid human-induced environmental change, posing great challenges for conservation. However, lack of assessment of specific habitat changes caused by anthropogenic disturbance limits effective conservation management for marine species in estuarine habitats. Here, using the Chinese white dolphin (Sousa chinensis) in Xiamen Bay as a case study, we used species distribution models to simulate Chinese white dolphin habitats during the late 1990s, early 2010s, late 2010s and early 2020 s, using historical occurrences and environmental variables interpreted from Landsat images. Over this time period, the Chinese white dolphin population experienced substantial habitat fragmentation and niche shifting. Driven by anthropogenic disturbance, the Chinese white dolphin population moved away from river mouths during 1994–2019, resulting a temporary increase in 50 % kernel density estimation (KDE) and habitat in early 2010s, followed by a decrease in the late 2010s. However, the population’s hypervolume decreased gradually to 32.1 % in early 2010s and 7.7 % in the late 2010s, reflecting loss of estuarine resources of the Chinese white dolphins. By early 2020 s, the 50 % KDE and habitat further decreased while the hypervolume increased to 58.2 %, probably due to availability of new estuarine habitats when the population colonized the northeast and southwest of this area. In conclusion, Xiamen Bay has gradually transformed from a refuge into an ecological trap for the Chinese white dolphin. In order to reverse this negative population trend, protected areas should be adjusted to include habitats in the Jiulong River Estuary, Weitou Bay, and the waters between them. Immediate interventions should be conducted to reduce anthropogenic disturbance and improve habitat quality. Ecosystem-based management and long-term monitoring are strongly recommended to avoid potential extinction of many other estuarine species caused by coastal urbanization.