Integrated multitrophic aquaculture (IMTA) allows to diversify production while reducing the footprint of a monoculture and is now widely recognized as a tool to increase the sustainability of aquaculture systems. Holothurians, or sea cucumbers, are excellent candidates for integration in IMTA, but European demonstrators are still scarce, mostly because of our limited capacity to reproduce European Holothurian species .
This presentation shares the latest results of a 15 months study testing the potential of growing Holothuria forskali underneath flat oysters, Ostrea eduli s. Juveniles specimen of H. foskali , fertilized and reared in controlled conditions up to 5g, have been stocked at different densities: 9 , 18 , 27 and 36 individuals/m2 under 3 rows of flat oysters in mesh bags placed above the intermediate shoreface. Growth and survival have been monitored and showed exceptional results, with a 95% survival and body masses multiplied by more than 20 for the lowest density . Despite slower growth observed for higher densities, total biomass was multiplied by 6 in the highest density, which translated in a 1035 g/m2 gain. These results demonstrate the great potential of growing H. forskali in combination with the studied oyster production system, in order to diversify production and income with neglectable extra efforts, time and investment.
Yet, to qualify an aquaculture production system as IMTA , trophic links need to be demonstrated in order to prove that holothurians benefit from the waste of the other species. A supplemental condition was therefore added and consisted in juvenile H. forskali stocked in similar conditions but outside the waste plume of the oysters. Surprisingly, growth was identical as below the oysters indicating that H. forskali can benefit from suitable food independently from oysters’ waste . Isotopic analyses and fatty acid compositions of the different conditions help better understanding trophic relationships in the system.