- Mangroves sequester carbon efficiently and are essential for climate change mitigation. The shift from agriculture to aquaculture causes land and water degradation and disrupts traditional livelihoods.
- Sustainable aquaculture requires addressing significant environmental concerns through practices like IAA and IMTA.
- Accurate spatial mapping and tracking of aquaculture ponds aid in marine spatial planning, assess environmental impacts, and support Sustainable Development Goals (SDGs) by informing effective management and policy decisions.
- Accurate spatial mapping and tracking of aquaculture ponds aid in marine spatial planning, assess environmental impacts, and support Sustainable Development Goals (SDGs) by informing effective management and policy decisions.
“Sustainable aquaculture is about more than just producing seafood; it’s about creating a system that works in harmony with our environment.” – Dr. Claude Boyd
Ecological Importance of Mangroves
Mangroves are tropical forests that grow in the intertidal zone of tropical and subtropical shores. They are among the most carbon-rich forests in the tropics and can sequester carbon much faster than other forests. This process can continue for millions of years, making mangroves critical in the fight against climate change. The amount of carbon stored within sediments of individual mangrove ecosystems varies widely, with a global median value of 2.2%.
Coastal aquaculture, particularly shrimp farming, has been heavily criticized for its environmental impacts, including the devastation of mangrove forests. Despite this, mangroves are ecologically and economically invaluable, offering various ecosystem services and biodiversity conservation. This deforestation also exacerbates various climatic variables such as coastal flooding, cyclones, droughts, rainfall changes, salinity, sea-level rise, and sea surface temperature increases, dramatically affecting coastal aquaculture. The mean ecosystem carbon stocks in shrimp ponds are significantly lower than in relatively intact mangroves. For example, shrimp ponds hold about 499 ± 56 Mg C ha−1 compared to 1023 ± 87 Mg C ha−1 in intact mangroves. This translates to a potential annual emission factor over 16 years following mangrove conversion of 120 Mg CO2e ha−1 yr−1. Including carbon losses from land use changes in a life cycle analysis revealed an estimated 2250 kg CO2-e emitted for every kilogram of shrimp produced in mangrove-converted ponds.
Also, this conversion of mangroves to aquaculture ponds has increased nutrient export from land, negatively impacting adjacent seagrass meadows and coral reefs. This highlights the persistent ecological and biogeochemical changes associated with mangrove conversion in tropical estuaries, affecting the ecosystem services provided by undisturbed mangrove forests.
Aquaculture's impact on Land use and its Socio-economic Effects
Agriculture remains the dominant land use in many areas and is often utilized for aquaculture and buildings. A significant concern is the extensive clearing and conversion of natural habitats for shrimp farming and agriculture, and, more recently, the shift from agriculture to aquaculture has sparked the conflict, leading to land and water degradation. This trend is driven by high global demand for aquaculture products and technological advancements, resulting in rapid and often unplanned coastal development.
Common pool resources have been converted to private use, reducing sharecropping opportunities and access to grazing land. The labour requirements for shrimp farms are lower than paddy production, leading to “absolute desensitization”, where many middle- and low-income residents have been displaced to pursue industrial labour in urban areas or become low-wage workers in aquaculture. However, many farmers in Bangladesh report higher and more reliable rice yields after converting their fields to ghers (ponds), improving food security for many.
Economic and Nutritional Impacts of Fish and Shrimp Consumption Fish and shrimp are generally more expensive than staple grains, pulses, or vegetables, leading to the contention that economic access and consumption improve with increasing consumer wealth and income. Urbanization further boosts fish consumption by offering better market access than rural areas. Over the past five decades, per capita fish supplies have increased by more than 60%, reaching 18.9 kg per person per year in 2010. However, at the local and household levels, case studies in Bangladesh indicate that farmed fish, often grown larger and consumed filleted, may offer lower nutritional contributions than wild small indigenous fish, typically consumed whole. There is no clear evidence that increased farmed fish supplies directly impact the micronutrient status of producing households and consumers.
Challenges in Management for Shrimp Cultivation
In the Indian Sundarbans Biosphere Reserve (SBR), extensive and illegal land conversion from agriculture to aquaculture over the past two decades has significant implications for SDGs related to food, poverty, employment, and ecosystems.
Studies show that in villages like Phong Thanh, Ninh Thanh Loi, and Vinh Loc in Vietnam, farmers, driven by higher shrimp revenues than rice, employ various techniques to maintain saline water in their fields for extended shrimp cultivation. This practice renders subsequent rice crops unviable, even in the rainy season, necessitating the harmonization of land management and water management at different levels, including farm and canal systems.
Environmental Challenges and Sustainable Practices
Despite the high market demand for fish and shrimp and their importance for food security, the growth of aquaculture presents significant environmental challenges. Various environmental and ecological concerns, including land, water, feed, and energy use limit sustainable aquaculture. The greening of aquaculture through Integrated Aquaculture-Agriculture (IAA) and Integrated Multi-Trophic Aquaculture (IMTA) could play a significant role in reversing the trend of blue carbon emissions and enhancing coastal ecosystems.
A study evaluated the dynamics of mangrove deforestation, aquaculture pond building, and subsequent abandonment in the Mahakam Delta, Indonesia. Historical data showed that 62% of the area had been deforested at an average annual rate of 4.5%. With increasing recognition of the importance of mangroves, rehabilitating aquaculture ponds back to mangrove forests has gained popularity. The thresholds for mangrove recruitment varied greatly across ponds and were correlated with elevation but not with distance to open water, salinity, or soil properties. Natural recruitment is a cost-effective way to rehabilitate mangroves at fluvial sites with favourable soil properties. Still, planting can speed up rehabilitation and increase species diversity at less favourable oceanic sites. Invasion of exotic species should be considered during pond rehabilitation.
A time series of very high spatial resolution optical satellite images from 2001 to 2015 revealed trends in the evolution of mangrove forests within aquaculture ponds. The results showed that mangroves are expanding both inside and outside of ponds. However, the yearly expansion rate varied significantly between replanted ponds. Ground truthing revealed that only Rhizophora species had been planted, while natural mangroves comprised Avicennia and Sonneratia species. Dense Rhizophora plantations had low regeneration capabilities compared to natural mangroves.
Governance Approaches in Fisheries and Aquaculture
Decentralized governance approaches, including co-management and community-based management, are prevalent in capture fisheries, emphasizing various social and environmental objectives. These approaches feature diverse institutional designs and varying community, state, and private sector participation levels. In contrast, aquaculture governance primarily focuses on the technical upgrading production to foster improved or “better” management standards. This aims to enhance efficiency and mitigate adverse environmental and social impacts. While the latter showcases successful technical implementations of different standards, it also highlights the weak inclusion of small-holder producers and the challenges of governing “off-farm” common resources sustainably and ethically.
“We need to rethink our approach to aquaculture, integrating it more thoughtfully into our coastal ecosystems.” – Dr. Niels Kautsky.
Research’s Ecological Importance
Our research is valuable in several critical ways for spatial planning by accurately identifying the latitude and longitude of aquaculture ponds, facilitating the creation of precise spatial maps, ensuring that aquaculture activities are situated in suitable areas, minimizing conflicts with other marine uses, and protecting sensitive habitats and coastal waters.
Tracking temporal changes in aquaculture ponds allows MSP (Marine Spatial Planning) to assess environmental impacts over time, which is crucial for evaluating the sustainability of aquaculture practices and their effects on ecosystems and helps estimate the lifespan of aquaculture ponds. Furthermore, detailed spatial data aids in resolving conflicts between various marine activities, such as fishing, tourism, and conservation, enabling more efficient space allocation. This also supports SDGs by promoting sustainable aquaculture practices that balance economic growth with environmental protection, contributing to food security and economic development.
Monitoring spatial and temporal dynamics also offers insights into the impacts of climate change, helping MSPs develop adaptive strategies. Additionally, our research enhances resource management by providing detailed information on the location and condition of aquaculture ponds, ensuring optimal and sustainable resource allocation.
Susank Chigilipalli, MRC Intern, IIT Kharagpur
About Author
Susank Chigilipalli is an undergraduate student from the Department of Civil Engineering at the Indian Institute of Technology (IIT), Kharagpur. He is skilled in Data Analytics and Computer Vision and interned at the Maritime Research Centre in Pune in the summer of 2024.