Functional traits of macrobenthos substantially indicated habitat change from the invasive saltmarsh to introduced mangrove.

ABSTRACT

Mangrove afforestation is usually thought to be beneficial to mitigate the degradation and loss of mangroves. In Southern China, planting mangroves with the introduced Sonneratia apetala is also supportive to remove the invasive Spartina alterniflora. However, the influence of mangrove afforestation dominated by introduced species on macrobenthos, a vital joint of energy flow and nutrient cycling in mangroves, remains unclear. We explored the linkage between the functional traits of macrobenthos and the physicochemical properties of sediments in a coastal continuum including the mudflat (MF), exotic Spartina alterniflora saltmarsh (SL), natural Avicennia marina forest (AM), and introduced S. apetala afforestation (SA) via a seasonal field survey. After removing the S. alterniflora invaded into mudflat via S. apetala afforestation, the sediment C/N ratio decreased compared to that of natural forest, while the concentrations of microphytobenthic chlorophyll-a increased. The macrobenthic inhabiting mode shifted from epifaunal to infaunal as well. The biomass and density of microbenthic community decreased along MF, SL, AM, and SA. SL had greater C/N ratio and smaller functional richness (FR) than MF. AM was characterized by similar functional diversities, and pH value and salinity of sediment to those of MF, and greater microphytobenthic chlorophyll-a was found in AM. Compared to AM, the introduced S. apetala substantially engineered the habitat due to its flourishing above-ground pneumatophore system which caused faster deposition process, subsequently changed the resource utilization strategies of macrobenthos considerably. Overall, the use of Sonneratia afforestation on Spartina removal could not replace the contribution of natural Avicennia forest with respect to the functional traits of macrobenthos. Careful consideration on ecosystem functionalities would be indispensable for conducting saltmarsh eradication and mangrove afforestation in the future.