Effects of invasive cordgrass on crab distributions and diets in a Chinese salt marsh

Abstract

The effects of invasive cordgrass Spartina alterniflora on burrowing crab communities in the salt marshes of the Yangtze River Estuary, China, were studied. Crab abundance, distribution and diets were compared in native Phragmites australis and invasive S. alterniflora stands. Spartina- invaded stands had 42% higher crab density than did native P. australis stands, largely because 2 dominant grapsoid crabs, Helice tientsinensis and Chiromantes dehaani, thrived in S. alterniflora stands. Sediment grain size, water content and vegetation stem height were the main factors corre- lated with crab distributions. Crab diet analyses revealed that crab stomach fullness was similar in stands of different plant species, indicating that in Spartina-invaded stands crabs can find compati- ble food quantity as in native plant stands. Both H. tientsinensis and C. dehaani from S. alterniflora stands had significantly higher δ 13 C values than those from P. australis stands, suggesting that the crabs consumed S. alterniflora in the invasive marshes. This non-selective feeding may be driving the success of H. tientsinensis and C. dehaani in invasive Spartina stands.