# Lessons for Coastal Applications of IMTA as a Way towards Sustainable Development: A Review
## 1 Introduction  
Aquaculture is the food-producing sector with the highest annual growth rate [1]. Production has increased steadily over the past three decades and will likely continue to do so in the future to ensure the needs of a more populous and affluent world [1]. Aquaculture is widely recognized as an important strategy for food security and poverty eradication [2], addressing at least seven of the 17 United Nations Sustainable Development Goals (UN SDGs) [3], and it plays an important role in ensuring human food security and nutrition in the future, as wild fisheries fail to meet the demand for aquatic products [4]. Fish contributes to around 20% of total animal protein intake [5] and is one of the cheapest sources of animalprotein. Over recent decades, the contribution of aquaculture to global fish output has increased, reaching 82.1 million tons (46%) of the estimated 179 million tons of global production in 2020, and this is expected to rise to 53% by 2030 [4]. This is mostly due to the commercialization of farm-raised aquatic animals such as shrimp, salmon, bivalves, tilapia, and catfish [6]. With the growing scarcity of freshwater, aquaculture growth may increasingly occur in marine and coastal environments. Ongoing environmental change processes, global population growth, and fisheries and food availability trends also imply a steadily increasing role for coastal aquaculture across the globe. This has raised concerns about environmental consequences and conflicts of aquaculture with other coastal uses in Europe, North America, Australia, and Asia [6]. At the same time, the available space for coastal aquaculture is altering: by 2080, sea level rise is expected to have turned approximately twenty percent of coastal wetlands into marine spaces [7]. The use and wastage of aquaculture feeds can negatively affect surrounding ecosystems. Feed waste and faecal production contribute to significant organic matter and nutrient loadings in marine and coastal ecosystems. Feed wastage can reach up to 38%, and this is one of the most significant sources of pollution [8; 9]. Several countries have also imposed restrictions on the practice of chemotherapeutic agents and reduced the use of feed additives, such as antibiotics and oil, in aquaculture feeds [10; 11], rendering classical single cultivar aquaculture less viable. Nonetheless, current aquaculture practices cause the eutrophication of coastal and other aquatic systems [12]. It is important to increase the understanding of how intensive and single species (monocultural) aquaculture generates deleterious environmental and social impacts. This has raised interest in ecosystem-based aquaculture such as integrated multi-trophic aquaculture (IMTA) [13; 14]. IMTA integrates aquatic organisms from various trophic levels in order to mimic ecosystem functions (Figure 1) [15; 16; 17; 18; 19]. Waste material from production in higher trophic layers (i.e., of finish and crustaceans) serves as food for organisms cultivated at lower trophic levels that transform the otherwise wasted and polluting resources into valuable products. Waste is thus minimized or eliminated and the overall productivity of the food system boosted [20; 21; 22]. It has been argued that IMTA is capable of supporting ecologically, environmentally, and socially viable aquaculture with economic viability [23]. By using the by-products of some cultivars to produce further useable or marketable plants and animals, it may support ecological sustainability through biomitigation, economic security through product diversification and risk mitigation, societal acceptance through better management, and social sustainability through a wider spread of aquaculture benefits than what is possible through conventional aquaculture. The main potentials of IMTA are thus environmental neutrality, economic viability, and social sustainability [24], although MTA can improve the long-term viability of aquaculture by generating environmental, economic, and social benefits.