Functional and trophic variations in macrofaunal assemblage reflect the ecological effects of bottom-based clam farming

Abstract

• The assemblage shifted towards a higher trophic level. • More complete utilization of resources was observed. • Clam farming provide biodeposits as additional food sources. • Functional and trophic diversity increased after clam farming. Understanding the ecological effects of bivalve farming on the ecosystem is needed to develop a responsible approach to marine management. The variations in the functional and trophic structure of the macrofaunal assemblage could be ideal indicators of these potential ecological effects. In this study, macrofaunal assemblage were investigated the in a bottom-based Manila clam farm located in Laizhou Bay, China before and after farming for one year, in order to identify the functional and trophic responses of the macrofauna and their feeding relationships to Manila clam farming. Stable isotope (SI) based trophic responses and trait-based functional responses of macrofauna were used to evaluate the ecological effects of the farming activity. After farming for one year, macrofaunal δ 15 N increased from 4.93 to 6.09‰, which was mostly caused by the presence of higher trophic-level carnivores. The standard ellipse area (SEAc) of detritivores shifted mainly through a decrease in δ 13 C range from 7.07 to 4.23‰, indicating the diet of this feeding group relied more on the biodeposits generated from farmed clams. Additionally, the diet of the carnivores after one year of clam farming mostly relied on detritivores (62.97%) rather than on farmed clams. Our study illustrated that clam farming could benefit the macrofaunal assemblage by providing biodeposits as additional food sources, consequently enhancing functional and trophic diversity. Moreover, the enhanced diversity occurred mainly in high trophic levels, leading to more complete utilization of resources. Therefore, our study suggested positive ecological effects of the bottom-based Manila clam farm on the macrofaunal assemblage after the first year of the activity.