Resource Availability and Use in Restored, Unmanaged, and Aquaculture Mangrove Ecosystems in Indonesia

Mangrove ecosystems are some of the most productive on our planet but have declined globally by 30–50%. Many species rely on mangrove habitats; thus, their conversion to aquaculture farms has led to noticeable losses in commodities such as wild fish stocks. This study aimed to assess the influence of aquaculture and restoration projects on the ecosystem’s ability to provide resources. We collected data on mangrove vegetation (i.e., biomass, richness, and abundance), soil nutrients (i.e., organic carbon, aluminium, and nitrogen), crab abundance, and fishing pressure at six sites. We set up 15 plots at each site and collected data between May and July 2023. Via generalised linear mixed models, we found that the abundance and richness of crabs was significantly higher in aquaculture plots than in non-aquaculture plots. Aquaculture plots had higher topsoil aluminium, higher topsoil and subsoil nitrogen, and lower topsoil carbon than non-aquaculture sites. Restored sites had less nitrogen in the topsoil than unmanaged sites. The biomass did not change between aquaculture, restored, and unmanaged plots. We found a negative correlation between crab abundance and richness and mangrove diameter at breast height (DBH), suggesting that the species of crabs present preferred areas with propagules for feeding (e.g., Grapsidae crabs). The content of nitrogen in the subsoil was positively correlated with mangrove richness, diversity, and height, suggesting the importance of nitrogen availability for mangrove growth. The content of aluminium in the subsoil was negatively correlated with the content of organic carbon in both the topsoil and subsoil, suggesting the detrimental effect of aluminium on the carbon cycle. Fishing practices were observed at all sites during the data collection period. Despite the lack of significant impact on most vegetation parameters and the limited differences between managed and unmanaged sites, key variables such as soil aluminium, carbon, and nitrogen contents and crab assemblages exhibited high variability, highlighting the complex interactions within mangrove ecosystems.