Return of the native: Survival, growth and condition of European oysters reintroduced to German offshore waters

Abstract

The European oyster (Ostrea edulis) is under significant threat across its natural distribution range and even functionally extinct in some regions, such as in the German North Sea. Due to its ecological significance in terms of biodiversity and other ecosystem services, the species, and the habitat it provides, are defined as highly endangered by the OSPAR Convention. Restoration measures are gaining momentum in Europe and conclusive recommendations for large‐scale biogenic reef restoration are relevant for example within the Marine Strategy Framework Directive and the Habitats Directive. This study examined whether present‐day environmental conditions of sublittoral offshore waters are ecologically suitable for the return of European oysters. Seed oysters (shell length ~2 mm) were deployed in cages in offshore field experiments in 10–26 m water depth. Survival, growth, and condition were investigated over the course of 2 years. Survival was high, even over winter. Growth was excellent, with oysters reaching a mean length of 55.0 ± 7.2 mm shell length and 19.2 ± 6.1 g wet weight after 2 years. The formation of firmly aggregated oysters was observed and confirms O. edulis as a reef‐building species. The overall condition of oysters in the field was excellent, identified by high condition indices and early reproductive activity. These findings are highly relevant for future restoration measures in the North Sea as they confirm that present‐day environmental conditions and small, hatchery‐produced seed oysters are suitable of supporting sustainable and successful restoration efforts even in sublittoral offshore waters.

Chromosome‐level reference genome for European flat oyster (Ostrea edulis L.)

“…Furthermore, it is thought >700 million oysters were consumed in London alone during 1864 (Pogoda, 2019 ). However, overfishing and anthropogenic activities have driven the collapse of O. edulis stocks throughout its natural range (Merk et al, 2020 ; Pogoda, 2019 ). The past 40 years have witnessed a further decline in production, with a peak of 32,995 tonnes in 1961 dropping by >90% to 3120 tonnes by 2016 (FAO, 2020 ).…”

Chromosome level reference genome for European flat oyster (Ostrea edulis L.)

“…Furthermore, it is thought >700 million oysters were consumed in London alone during 1864 (Pogoda, 2019a). However, overfishing and anthropogenic activities have driven a collapse of O. edulis stocks throughout its natural range (Pogoda, 2019b; Merk et al, 2020). The past 40 years has witnessed a further decline in production, with a peak of 32,995 tonnes in 1961 dropping by >90% to 3,120 tonnes by 2016 (FAO, 2020).…”

The late Holocene demise of a sublittoral oyster bed in the North Sea

“…Spatial shifts in the ecological quality of the environment, which can occur on shorter or larger time scales, drive the extension and health of oyster populations with regard to sedimentation rates and food availability. This stresses the importance of holistic approaches to inform the restoration and conservation of marine habitats [ 78 , 82 ]. More specifically, the site selection for restoration measures needs to consider the potential impact of sedimentation as crucial factors [ 19 ].…”