Design, dimensioning and performance of a large-scale flat oyster (Ostrea edulis) broodstock conditioning at Helgoland Oyster Hatchery

Restocking and conservation of European flat oyster (Ostrea edulis) populations is a major focus of ecological restoration efforts to benefit from the wide range of ecosystem functions and services that this species provides by building up biogenic reefs. Today, O. edulis production is still largely based on seed collection through the placement of collectors in the wild. Given the specific requirements for ecological restoration, such as the absence of pathogens and the preservation of a high genetic diversity, the current supply with seed oysters within Europe is insufficient or inadequate. Moreover, in the German context where no native broodstock occurs and pathogens are absent, ecological restoration can only be carried out by establishing an innovative research oyster hatchery using appropriate imported oyster broodstock for controlled production. In this context this study was carried out on the island of Helgoland, addressing the requirements of: 1) substantial larval production, 2) design and construction of an effective broodstock conditioning system (against the constraints of converting an existing infrastructure from the 1970s and space limitations, 3) bio secure production. The focus of the study was the design, implementation of the conditioning structures (broodstock maturation), the validation (conditioning) of the conditioning system and the performance evaluation (number of larvae, influence of temperature, influence of broodstock origin) of the implemented structure. The inseparable aspects of biosecurity (including quarantine, purification treatments), broodstock production and feeding, and pre-conditioning operations are also addressed here. After planning period (February 2021 to April 2021), the designed system was build up (April 2021 to May 2021) and activated with broodstock oysters from two origins (Norway and Scotland) for a first conditioning cycle (June 2021 to September 2021). In total 32 million O. edulis larvae were produced successfully