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Until the late 19th century, extensive beds of flat oyster Ostrea edulis populated the Central North Sea, which have vanished after intensive fisheries. At present, various initiatives are being carried out to investigate the potential to restore this former key species in the area. This historical ecological study contributes by delineating the former oyster bed area and through an assessment of its limits against known gradients in the North Sea. Extensive data from historical maps, texts, and ship-based surveys were used to synthesize our knowledge on the former beds. It was revealed that the area with oyster beds covered ∼6.2% of the total North Sea bottom, with a delineation that could partly be explained by hydrodynamic and temperature gradients. The position and extent of the area are notably different from the area that is used in recent feasibility studies on the restoration of North Sea oyster beds. The offshore oysters lived on muddy sand in relatively cold conditions, and there are several indications that their reproductive rate was low. The apparent disappearance of cold water adapted flat oysters will challenge restoration projects. This study provides indispensable information for the future restoration of flat oyster beds in the North Sea.

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Only a few records exist of the sponge crab Dromia personata in the North Sea. Most records are in local languages, and have limited availability. On 11 August 2016, D. personata was found by divers in the Eastern Scheldt, a former estuary in the south-western part of the Netherlands. In the months to follow, at least four other individuals were observed by divers at the same and nearby locations. This paper lists these and former records in the North Sea. The distribution pattern, and the possible migration of the sponge crab in relation to environmental conditions such as seawater temperature are discussed, as well as the crab's use of the non-native sponge Celtodoryx ciocalyptoides.