Mama’s Clams: Environmental Performance of an Extended Nursery Phase for Manila Clams—Sand-Nurseries as a Potential Strategy to Address Juvenile Scarcity

Between 2014 and 2023, Italian Manila clam (Ruditapes philippinarum) production declined by 36% due to climate change and predation by the invasive blue crab (Callinectes sapidus), which preys particularly on small clams. Traditionally, Manila clam farming starts with seed collection from natural recruitment or hatcheries, followed by pre-fattening in raceways and/or FLUPSY (Floating Upweller Systems) to size T3 (>3 mm). The fattening phase in lagoons up to the commercial size (>25 mm) follows. Rearing juveniles in controlled conditions may ensure stable supplies of high-quality seed, reduced mortality, and increase overall yields. Furthermore, a larger pre-seeding size (e.g., T10, >10 mm) is supposed to improve resistance to predators and environmental stress. This study uses an ex-ante Life Cycle Assessment (LCA) to evaluate the potential environmental impacts of a novel and unique “sand-nursery” method under development at an Italian company. The nutrient removal potential of juvenile clams was also assessed as an ecosystem service. At full capacity, the optimised system could produce 120 t of liveweight juveniles and remove 338 kg of nitrogen and 32 kg of phosphorus. Although it has inherent limitations, the ex-ante LCA results show that electricity consumption is the main contributor to environmental impacts, with a global warming potential of 1.11 kg CO2 eq/kg T10 clam. Further research is needed to assess impacts across the full production cycle.