Use of macrofaunal assemblage indices and biological trait analysis to assess the ecological impacts of coastal bivalve aquaculture

Coastal bivalve aquaculture is considered to have large impacts on the structure and functions of macrofauna assemblages. In the present study, we evaluated the macrofauna assemblages from 12 bivalve farms along the China coast using 11 compositional and functional indices and 15 biological traits within four major categories. Linear mixed models (LMMs) were used to identify the most influential variable on the selected indices. The RLQ and fourth-corner approaches were used to investigate the response of functional traits composition to the characteristics of bivalve farms. Our results suggest that the increased densities of cultured bivalve had a negative impact on the organisms sharing similar function traits but the ecosystem could still maintain the functional richness because those organisms were mainly on the redundant group, and their loss favored a more balanced distribution of taxa and biological traits. Additionally, biological trait compositions of macrofaunal assemblages were more similar within farms using the same culture method. Small-sized opportunistic deposit feeders were likely to appear in cage farms, and predators were more attracted by rope farms. In bottom-based bivalve farms, filter feeders dominated but carnivores and crawlers were significantly lower compared to the other culture methods. We conclude that functional redundancy is a critical indicator for identifying the suitable scale and intensity of bivalve aquaculture. From the perspective of maintaining biological traits, bottom-based culture causes less ecological impact compared to off-bottom culture, the latter is more suitable in areas with relatively deep water and strong current and water exchange rate.