Threshold of island anthropogenic disturbance based on ecological vulnerability Assessment-A case study of Zhujiajian Island

The accessibility of islands can be largely improved with fixed link to the mainland by the construction of sea cross bridges and tunnels, which results in a rapid increase of tourists and economic income. Meanwhile the accelerated increase of built-up land will change the island land use deeply. As the main anthropogenic disturbance, the rapid change of land use and increase of tourists will set further pressure on the ecological vulnerability of islands. It is urgent to derive the threshold of anthropogenic influence on the island with fixed link to the mainland. Island Ecological Vulnerability Index (IEVI) is used to evaluate the ecological vulnerability of Zhujiajian Island. Land use and tourists change in the next 20 years is simulated to estimate the change of island ecological vulnerability. The main results are: 1) The ecosystem of Zhujiajian Island is in good condition now, with limited area at moderate and severe vulnerable status; 2) With the rapid increase of anthropogenic disturbance, the ecological vulnerability of the island tends to increase. During the research period 2015-2035 the area of severe vulnerability increases by 78%, and the area of mild vulnerability increases by 201 ha (33%). One third of the non-vulnerable area becomes vulnerable; 3) Based on the prediction of ecological vulnerability, the threshold of tourists in Zhujiajian Island is about 16 million per year. The upper limit of built up area is 2500 ha, which means 90% is already used. With the improvement of management effectiveness and waste treatment capacity, the island's anthropogenic disturbance threshold can be raised. The vulnerability based anthropogenic disturbance threshold analysis can provide a basis for viable island ecosystem management strategies.