Environmental legacy of aquaculture and industrial activities in mangrove ecosystems

Aquaculture and industrial activities have been recognized for their detrimental impact on coastal environment, particularly through large-scale mangrove conversion. This study employs interdisciplinary spatial, geochemical, and metagenomic approaches to examine the environmental legacy of past aquaculture and industrial activities in mangrove rehabilitation areas. The land use change of mangrove, aquaculture, and industrial area was investigated from 1990 to 2020. Mangrove coverage increased in the study area from 49.12 ha in year 1990 to 95.93 ha in 2020. This growth can be attributed to increasing environmental awareness related to issues such as tidal flooding, seawater intrusion, and coastal abrasion. However, despite increasing mangrove coverage, we still identified fecal bacteria communities in both sites, dominated by Campylobacteria, Gammaproteobacteria, and Deltaproteobacteria. Additionally, our functional prediction analysis revealed the presence of genes associated with pathogenicity, multidrug/antibiotic resistance, and xenobiotic degradation. We observed high nitrate concentration associated with aquaculture waste that was persistent in porewater even after the activity ended years ago. Low to moderate heavy metal concentration was found in the study sites, likely due to the role of mangroves as a biofilter. We conclude that mangrove restoration contributes to the lower environmental impact of anthropogenic activities on our sites. Therefore, it should be included in future coastal management plans to improve coastal water quality and ecosystem function in environmentally threatened areas.