Significant but short time assimilation of organic matter from decomposed exotic Spartina alterniflora leaf litter by mangrove polychaetes

Abstract

Leaf litter is an important nutrient source for benthic communities within mangrove ecosystems and in adjacent areas. Exotic Spartina alterniflora invasion to the eastern coastlines of China has been shown to alter trophic relationship of benthos in mangrove wetlands, but little is known about potential effect of exotic litter decomposition on food sources of benthic macrofauna. We took the advantage of significant differences in the δ13C values of exotic S. alterniflora (C4 plant) from a native mangrove species Kandelia obovata (C3 plant) to investigate leaf carbon assimilation by polychaetes during litter decomposition. We found that exotic S. alterniflora leaf litter decomposed more slowly than that of native mangrove species at the mangrove site (P = 0.003), but there was no significant difference between them at the salt marsh site (P = 0.270). The polychaetes assimilated major organic matter from K. obvata and the particulate organic matter (> 90%) at the mangrove site. But the polychaetes assimilated major organic matter from S. alterniflora (> 60%) at the salt marsh site. However, after adding S. alterniflora leaf litter at the mangrove site, polychaetes assimilated more carbon from S. alterniflora (> 45%) than that from K. obovata (< 25%). Furthermore, the significant carbon assimilation only occurred within a short period time (1–2 months) during decomposition. Our results suggested that Spartina invasion can change food sources of local mangrove polychaetes through utilizing the organic matter released from litter decomposition, but such assimilation of exotic foods is of short time nature.