Introduction
The necessity for novel sources of natural products is increasing, positioning marine organisms as promising sources of sustainable food and biomaterials. Ascidians (Phylum: Chordata, Subphylum: Tunicata) , or ‘sea squirts’ , are marine filter-feeding invertebrates known for their rich chemical diversity and potential biotechnological applications (Palanisamy et al., 2017). Notably, they are the only known animals capable of producing cellulose (Xiaoyu et al., 2023) . Styela plicata is a solitary, cosmopolitan ascidian often found in high densities on artificial structures in harbors and marinas. It is also recognized as a species that can interfere with aquaculture operations by fouling equipment and competing with farmed or native filter feeders (Pineda et al., 2013). It thrives in a wide range of environmental conditions, including high temperatures , salinity, and pollution (Platin & Shenkar, 2023), making it a strong candidate for aquaculture. In South Korea, S. plicata is consumed as a traditional seafood, valued for its high protein content and bioactive compounds with antioxidant and antimicrobial properties (Lambert et al., 2016 ). However, cultivation practices remain limited, and no standardized inland protocol has been established for this species to date. Moreover, individuals are often collected from highly polluted areas, which may affect their nutritional value. During a previous study (Platin, 2022), S. plicata demonstrated rapid growth and high reproductive output in a closed-water system, supporting its feasibility for scalable aquaculture. Notably, S. plicata produces a thick outer tunic (an external layer that protects the animal’s soft body) composed of approximately 60% cellulose. Their cellulose is highly crystalline and exhibits exceptional mechanical, electrical, and magneto-responsive properties, positioning it as a promising source of tunicate nanocellulose (t-CNC) for industrial applications (Xiaoyu et al., 2023). This study introduces a controlled cultivation protocol for the early life stages of S. plicata , providing a basis for evaluating its potential in future applications related to food production and biomaterials. G iven its physiological resilience and ability to grow in nutrient-poor conditions, S. plicata emerges as a promising candidate for resource-efficient marine cultivation targeting food and industrial biomaterials.
Materials and methods
This study consisted of a series of controlled experiments designed to evaluate the growth performance and survival of Styela plicata juveniles under various rearing conditions , including food type (two algae and their mix) , light intensity (low light vs. complete darkness), feeding frequency, and five different temperatures. All experiments were conducted in both Closed Water Systems (CWS) and Running Seawater Systems (RSS), except for the temperature experiment, which was performed exclusively in RSS. At the beginning of each trial, 5 to 13 adult individuals were collected from the field. Artificial fertilization was performed to produce same-age juveniles from the same parents, ensuring synchronized feeding across replicates. Survival and growth rate were measured weekly and served as the primary performance parameters, with 180 to 360 juveniles per experiment, depending on the trial. Each experiment lasted one month, except for the food type and concentration trial, which was conducted over a period of three and a half months.
Results and discussion
Juveniles of Styela plicata showed high survival in RSS when fed Nannochloropsis at the lowest concentration, with 75 ± 8.3% survival and an average size of 2.9 ± 0.2 mm after three and a half months. A mixed diet of Isochrysis galbana and Nannochloropsis at the highest concentration resulted in 83.3 ± 14.4% survival and a larger size of 3.3 ± 0.6 mm. For subsequent experiments, Nannochloropsis at the lowest concentration was selected as the standard feed due to its favorable survival rates and cost-efficiency. After one month, survival with Nannochloropsis X reached 100% in CWS and 77.7 ± 9.6% in RSS. Temperature had a clear effect on growth. The highest average size was recorded at 26 °C (840 ± 94 µm), with significantly larger individuals (p < 0.05) compared to 16 °C (581 ± 40 µm), 20 °C (501 ± 175 µm), and 30 °C (585 ± 65 µm). Survival was highest at 16 °C (72.2 ± 33.6%) and declined sharply at both 20 °C (38.9 ± 17.3%) and 24 °C (38.9 ± 5.3%). These results highlight a trade-off between growth and survival, emphasizing the need to adjust rearing conditions to production goals. S. plicata demonstrates strong potential for controlled aquaculture, with feeding regime and temperature identified as key factors. The use of Nannochloropsis as a single-species feed supports both biological efficacy and economic feasibility for scalable cultivation.
Conclusion
The protocol developed in this study is optimized for the early stages of S. plicata and provides a solid foundation for its future use in aquaculture as a source of dietary supplements and cellulose for industrial applications . Although additional research is needed to refine long-term rearing strategies and evaluate later life stages, our results highlight the species’ high reproductive capacity and its compatibility with open seawater systems. Notably , S. plicata was successfully cultivated in nutrient-poor Eastern Mediterranean seawater, demonstrating its robustness and potential for low-input marine production. Future studies should explore the species’ value as a dietary supplement and as a sustainable source of tunicate cellulose following controlled aquaculture.
References
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Pineda, M.C., López-Legentil, S. and Turon , X., 2013. Year-round reproduction in a seasonal sea: biological cycle of the introduced ascidian Styela plicata in the Western Mediterranean. Mar. Biol., 160:221-230.
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