Co-Culture of Gracilariopsis longissima Seaweed and Penaeus monodon Shrimp for Environmental and Economic Resilience in Poor South-East Asian Coastal Aquaculture Communities

A significant body of controlled laboratory research suggests different biological mechanisms by which the low-cost co-culture of seaweed and shrimp could improve sustainability whilst increasing income for the many poor pond farmers of South-East Asia. However, at the pond level, production and cost–benefit assessments remain largely lacking. Here, we studied the extensive co-culture of Gracilariopsis longissima seaweed and Penaeus monodon shrimp on pond production output, nutrient concentrations, and farm income on the north coast of Java, Indonesia. Co-culture showed 18% higher seaweed production during the first cycle (2261.0 ± 348.0 kg·ha −1 ) and 27% higher production during the second (2,361.0 ± 127.3 kg·ha −1 ) compared to monoculture. Shrimp production per cycle was 53.8% higher in co-culture (264.4 ± 47.6 kg·ha −1 ) than in single-species cultivation (171.7 ± 10.4 kg·ha −1 ). Seaweed agar content and gel strength did not differ between treatments, and neither did shrimp bacterial or heavy metals concentrations. The profit of co-culture was, respectively, 156% and 318% compared to single-species seaweed and shrimp cultivation. Co-cultivation lowered nutrient loading in the pond water and in the sediment and is argued to be a low-investment and environmentally friendly option for poor pond farmers to improve their income and financial resilience through product diversification.