Broodstock oysters are conditioned for reproduction by adjusting diet and ambient temperature. The larvae produced are then carefully raised and supplied with optimal feed. In the last larval phase prior to metamorphosis they are then transferred to settlement tanks, previously equipped with the desired substrate.
In the Helgoland Oyster Hatchery, the optimal rearing of larvae is ensured by a specifically designed water treatment system and state-of-the-art high density larval rearing tanks.
The different life stages of O. edulis are fed with microalgae species (Rhodomonas salina, Isochrysis galbana and Chaetoceros neogracilis), native to the German North Sea around Helgoland. The microalgae production is a crucial part of hatchery production. Here, parameters such as algae growth, algae biomass, biovolume, and contaminations (e.g. protist, ciliates, other algae species) are constantly recorded. When feeding the microalgae to the oysters, the ratio of different species and therefore nutrients is adapted individually to the different life stages.
The settlement substrate is chosen in compliance with the needs of restoration: For the ‘spat-on-shell’ approach, the larvae (spat) settle on European oyster shells; for the ‘spat-on-reef’ approach they settle on reef structures, made of natural materials. In the nursery, they grow on these substrates until they are released at the restoration sites. Once there, they continue to grow and, under favourable conditions, can reproduce in the wild, therefore contributing to the foundation of a new oyster population.
Helgoland Oyster Hatchery works closely with members of the NORA network and in particular with the Production Working Group. This working group aims to find a collaborative solution or common understanding of the barriers to oyster supply for restoration efforts.