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

Impact of cropland management on invertebrate richness and abundance in agroforestry systems in Bali, Indonesia

The intensive management of cropland refers to a reduction in habitat complexity (i.e., shade tree cover, tree species richness, crop species richness) to gain more profits. This usually entails a decrease in biodiversity, but agroforestry systems have been shown to provide a solution to the need for profits while maintaining biodiversity and ecosystem services. Invertebrates are important bioindicators since they are not just affected by a decrease in habitat complexity; they are also key for the maintenance of ecosystems given their ecological roles. We aimed to understand how agricultural intensification impacted invertebrate abundance and richness in an agroforestry system in Bali, Indonesia. We set up 53 × 25 m2 plots and collected data via pitfall and pan traps. We linked those data to vegetation data (canopy cover, tree species richness, crop species richness), habitat type (rustic vs. polyculture), and productivity. Overall, we found that the abundance and richness of invertebrate taxa were positively influenced by increasing canopy cover and crop and tree species richness. This supports the habitat heterogeneity hypothesis, which indicates that increased habitat complexity promotes higher invertebrate species richness and abundance. The abundance and richness of certain invertebrate taxa, including agents of biocontrol, were shown to increase in plots with higher yields, thus solidifying the important role of invertebrate communities in the provision of ecosystem services. Harvesting crops from complex agroforestry systems ensures a sustainable income for local communities as well as habitats for invertebrates

Developing a Mangrove Health Metric through the Evaluation of Mangrove Ecosystems in Indonesia

The conservation and restoration of mangrove ecosystems is increasingly needed to ensure their success. These ecosystems provide an array of benefits, both environmental and economical, however they are often removed for aquaculture, palm oil plantations or other uses. This occurs throughout Southeast Asia, with Indonesia being a country holding nearly one quarter of the world’s mangroves. Restoration efforts have been made in an attempt to repair mangrove ecosystems; however, this often produces monocultures, maintaining low levels of diversity. There is little understanding regarding the health of mangrove ecosystems. Whilst there have previously been studies investigating individual variables in individual environments, there are very few that look across multiple, with even less that access multiple variables across multiple ecosystems. Additionally, certain health indicators have been studied but only within a single region. This study looks at various indicators of health to highlight areas that could be used by organisations restoring these ecosystems as a way of monitoring the success of their project. Here we show how mangrove richness, diversity and abundance, above- and below-ground biomass, crab richness, diversity and abundance, water salinity, pH, DO and turbidity, fauna and fishing pressure could be potential indicators of mangrove health. In order to achieve this, various survey techniques were used to measure these parameters including, observations, transects and plots within different ecosystems. This study found that there were strong positive correlations between the crab richness and mangrove richness. Additionally, crab richness, diversity and abundance were all found to display a negative correlation with mangrove diameter and height. Furthermore, there was an observed relationship between the above-ground biomass and dissolved oxygen. These results, along with fauna and fishing pressure monitoring could potentially be variables used within long-term monitoring programmes. Much more research is need to track seasonal or short-term changes within mangrove ecosystems. However, the results within this study could be used to provide organisations and NGOs monitoring techniques and key insights into mangrove ecosystem health indicators. This could also have larger implications to support decisions made by stakeholders or local governing bodies as to the success of restoration projects