Cultivation of the polychaete worm Sabella spallanzanii (Gmelin, 1791) in a novel multi-species IMTA (integrated multi-trophic aquaculture) system in the Mediterranean Sea

The cultivation and biomass production of the worm Sabella spallanzanii (Gmelin, 1791) through local macrofouling recruitment on natural fiber ropes was investigated in an IMTA-converted fish farm in the Mediterranean Sea. Over a 19-month cultivation cycle, a species-rich macrofouling assemblage was obtained, reaching a final biomass of 19–24 kg per rope, with only four species (S. spallanzanii, Mytilus galloprovincialis Lamarck, 1819, Phallusia mammillata (Cuvier, 1815), and Paraleucilla magna Klautau, Monteiro & Borojevic, 2004) contributing to 86 ± 7 % of total biomass. Each species likely found favorable settlement conditions, exploiting available food resources and potentially helping to reduce/recycle excess organic matter. Despite high mortality, S. spallanzanii accounted for 66 ± 7 % of final macrofouling biomass, with about 210,000 worms (≈1-ton live biomass) produced at IMTA farm scale using 196 10-m-long ropes. The observed decline in abundance during the cultivation cycle (from 3393 to 1090 individuals per rope) followed an exponential decay model, while individual growth (0.25–5.06 g) was described by a logistic curve, projecting the optimal harvest time between months 22–30, with a biomass peak of 1.57 ± 0.85 tons. Chemical analyses showed elevated heavy metal concentrations in worm tubes and crowns, but body tissues remained below EU regulatory thresholds, supporting their safe use in fish feed. Additionally, due to their antimicrobial mucus and aesthetic features, worms show potential for both pharmaceutical and ornamental aquarium markets. These findings support S. spallanzanii as a valuable species for cultivation within IMTA systems, further highlighting the potential of macrofouling exploitation for integrated biomass valorization.