As part of the EU-funded ASTRAL project, the South African IMTA lab investigated two local sea urchin species (Tripneustes gratilla and Parechinus angulosus) grown in two different integrated multi-trophic aquaculture (IMTA) scenarios.
The urchin species investigated in the first case study, T. gratilla, has been taken from research- to pilot-commercial scale within the framework of the ASTRAL project. Hatchery-produced urchins were successfully grown in an IMTA system at Buffeljags Abalone Farm in South Africa . In this system, the dissolved nutrients released by the urchins were used as an input to grow Ulva , whereafter the Ulva was used as a feed or feed component for the urchins, thereby improving circularity in the IMTA system. An assessment of sea urchin feeding regimes and nutrient cycling in the IMTA system was conducted to identify best practices and recommendations for future commercial-scale land-based IMTA of this sea urchin species. A key outcome from this case study was that the nutrients in the particulate organic matter (POM) released by the urchins could be captured to further promote circularity in the IMTA.
The second case study was based on the Cape sea urchin P. angulosus, as there is a known natural relationship between the Cape urchin and juvenile abalone (Haliotis midae) along the South African coast. Juvenile abalone are predominantly found under the sea urchins, where they are likely seeking shelter and food, but there could also be a transfer of beneficial microorganisms from the urchins to the abalone as they have access to the urchin faecal matter and faecal matter-associated microorganisms. Therefore, Cape urchin faecal matter was assessed as a functional feed for juvenile abalone in a hatchery-scale trial. It was found that there are growth, survival and microbiome transfer benefits associated with the use of sea urchin faecal matter as a supplementary feed for juvenile abalone. To assess the Cape urchin as an additional product, a six- month growth trial was conducted using wild-collected P. angulosus , where results showed that gonad enhancement was possible in a short amount of time. However, further research is required to better understand the dietary requirements and growth of this species at different life stages.
This contribution will highlight species selection criteria, optimal growing conditions and key findings across the two sea urchin species investigated by the IMTA lab SA . Though T. gratilla and P. angulosus are in different phases of research and development, both case studies highlight the value of using co-products from one species as an input for another and show that these species have the potential to be cultivated using IMTA technologies.
This study received funding from the EU Horizon 2020 Research & Innovation Programme ASTRAL Project under Grant Agreement No. 863034.