Introduction
The flat oyster Ostrea edulis is a native European species known for its significant role in ecosystem services such as habitat creation and biofiltration. Historically abundant across the northeastern Atlantic and the Mediterranean basin, its populations have drastically declined due to overexploitation, habitat loss, and environmental degradation (Thurstan et al., 2024) .
O . edulis is increasingly being used in restorative aquaculture, which, when properly implemented, offers a promising and sustainable approach to ecosystem restoration. In the Mediterranean Sea, specifically in the southeast of Spain, the Mar Menor Oyster Initiative (MMOI, https://noraeurope.eu/spain-the-mar-menor-oyster-initiative/ ) is being carrying out . This initiative aims to study the nutrient extraction capacity of O. edulis in the hypersaline Mar Menor lagoon and to develop tools necessary for future restoration and bioextraction actions (Albentosa et al., 2023).
The main objective of this study is to increase the O . edulis stock to support ecosystem restoration efforts in the Mar Menor and to validate the reproduction of hatchery-produced oysters in 2022 (Hernandis et al., 2023), confirming their viability for successful breeding .
Material and methods
The reproduction of the oysters was carried out from March to May 2024 according to its natural reproductive season in the Mar Menor lagoon (SE Spain). It took place at the IEO-CSIC experimental hatchery using 69 broodstock individuals : 29 wild oysters from the lagoon (WB) and 40 hatchery-produced in 2022 (HB) in the same experimental hatchery .
Results and discussion
Spawning followed natural thermal cycles, producing a total of 36 spawns and 59.8 million larvae, 48% of which originated from HB (Figure 1) . These findings confirm for the first time that individuals bred in hatchery in 2022 (Hernandis et al., 2023) are reproductively viable. Larvae from WB were significantly larger (mean = 168.5 µm) than those from HB (mean = 153.3 µm), and their survival to settlement was also higher (54% vs. 21%, respectively). However, the survival rate to postlarvae stage was higher (24% ) for those larvae from HB than those from WB (16%) . The observed differences in fecundity and larval performance are consistent with age-related reproductive maturity: WB individuals were older and fully mature possessing greater energy reserves and more developed gonads , whereas HB were in their first reproductive cycle after reaching sexual maturity. This may influence reproductive outcomes, with older individuals typically having larger energy reserves and more developed reproductive organs (Bayne, 2017) .
This study demonstrates the reproductive potential of both wild and hatchery O. edulis from the Mar Menor, highlighting the viability of establishing a reliable stock of locally adapted native oysters. This integrates aquaculture into restoration frameworks allowing large-scale actions in the lagoon, aligned with global efforts to recover native oyster habitats and the ecosystem services they provide.
Acknoledgments
This study has been funded by the MITOYSTER (PID2022-139616OB-C31from the Spanish Research Statal Agency -AEI-) and THINKINAZUL (PRTR-C17.I1 , from the Spanish Ministry of Science and the Murcia Region) projects.
References
Albentosa, M., … Martínez, P. (2023). Recovery of eutrophized marine ecosystems using the European flat oyster, Ostrea edulis . Aquatic Conservation: Marine and Freshwater Ecosystems , 33 (7), 645–660. https://doi.org/10.1002/aqc.3926
Bayne BL (2017) Biology of Oysters. In: Bayne B (ed) Developments in Aquaculture and Fisherires Science. Elsevier, London, pp 209-329
Hernandis, S., da Costa, F., Hernández-Contreras, Á., & Albentosa, M. (2023). Hatchery seed production of flat oysters from the Mar Menor lagoon. Frontiers in Marine Science , 10. https://doi.org/10.3389/fmars.2023.1231686
Thurstan, R. H., … E zu Ermgassen, P. S. (2024). The world was our oyster: Records reveal the vast historical extent of European oyster reef ecosystems.