Suitable habitat mapping in the Yangtze River Estuary influenced by land reclamations

Abstract

We proposed an approach to calculate estuarine habitat suitability and habitat fragmentation by integrating various environmental factors. Based on fuzzy logic method, water depth, salinity, and fluctuation rate of salinity were integrated into a Habitat Suitability Index (HSI) to map suitable habitat pattern of target species in estuaries. Then the HSI is used to calculate Habitat Aggregation Index (HAI) that represents the degree of habitat fragmentation. The proposed method was applied to the Yangtze River Estuary which has experienced long term land reclamation activities during the past two decades including the transformations of coastal wetlands to urban infrastructures and the deep-water channel construction. We selected Chinese mitten crab (Eriocheir sinensis) as a target species in this study, the results indicated that under the impact of land reclamation in the Yangtze River Estuary the isoclines of low salinity moved seaward and the optimum salinity range for Chinese mitten crab has been compressed. The suitable habitat for Chinese mitten crab decreased 325.4km2 and the HAI has also decreased 2% during the first stage of land reclamation (scenario 1–scenario 2) with a transformation of 237.2km2 coastal wetlands to concretes. During the second stage of land reclamation (scenario 2–scenario 3), the combined effects of coastal wetlands disappearance (282.7km2) and deep-water channel construction (92.2km) have led to a degeneration of suitable habitat for Chinese mitten crab about 427.4km2 and HAI decreased 6%. Land reclamations in the Yangtze River Estuary not only directly occupied suitable habitat for the Chinese mitten crab, but also altered the habitat patterns and destroyed habitat connectivity, which showed high potential to affect the migration of this species. This proposed approach is flexible for habitat evaluation in estuaries.