Recent findings of wild European flat oysters Ostrea edulis (Linnaeus, 1758) in Belgian and Dutch offshore waters: new perspectives for offshore oyster reef restoration in the southern North Sea

Abstract

ABSTRACT. The European flat oyster, Ostrea edulis, is an emblematic and ecologically important species that was fished to virtual extinction in Belgian and Dutch waters in the 19 th century. We report on recent findings of live specimens in Belgian and Dutch waters, an indication for the presence of O. edulis in these waters. Though small, these relict populations provide possibilities for natural recovery of O. edulis reefs in Belgian and Dutch waters, provided the oyster's habitat requirements are restored (e.g., exclusion of bottom disturbance). We suggest investigating whether a natural, yet slow, recovery using fisheries closures and gravel bed restoration is a feasible alternative to the currently envisaged human-mediated re-introduction of O. edulis in the North Sea. We identify and address the challenge of O. edulis detection and identification as an important issue blurring the true presence and distribution of oysters.

Ostrea edulisat shipwrecks in the Dutch North Sea

“…Also, O. edulis has a relatively straight opening compared to Crassostrea gigas . In the collected specimen, presence of chomata in the hinge was confirmed, which is an important characteristic to differentiate between O. edulis and C. gigas (Amaral and Simone, 2014; Kerckhof et al, 2018).…”

“…To date, the European flat oyster was considered extinct offshore in the northern area of the Dutch part of the North Sea. Only in southern Dutch North Sea waters and in the Wadden Sea flat oysters had been observed recently (Bouma and Lengkeek, 2013; Christianen et al, 2018; Kamermans et al, 2018; Kerckhof et al, 2018). During visits of over 100 ship wrecks between 2010 and 2019 by the same group of wreck divers, no other live flat oysters were observed offshore (personal observations by the authors), with exception of locations in the south of the Netherlands and Belgium (Kerckhof et al, 2018).…”

“…Only in southern Dutch North Sea waters and in the Wadden Sea flat oysters had been observed recently (Bouma and Lengkeek, 2013; Christianen et al, 2018; Kamermans et al, 2018; Kerckhof et al, 2018). During visits of over 100 ship wrecks between 2010 and 2019 by the same group of wreck divers, no other live flat oysters were observed offshore (personal observations by the authors), with exception of locations in the south of the Netherlands and Belgium (Kerckhof et al, 2018). Furthermore, recent investigations of fouling communities on oil and gas structures near shipwreck #3251, did not reveal any flat oysters (Coolen et al, 2018), nor did a study of rocky reefs in the Borkum Reef grounds near the Gustav Nachtigal wreck (Coolen et al, 2015a).…”

“…Large white dots: absence observations on all other wrecks inspected in July and September 2019. Medium sized grey dots off the coast: sightings offshore (OWEZ windfarm and HMS Aboukir; Kerckhof et al, 2018). Medium sized white dot with black centre: unconfirmed sighting offshore (Christiaan Huygens wreck; Kerckhof et al [2018]).…”

“…Nowadays, the flat oyster is considered extinct offshore in the Netherlands (Berghahn and Ruth, 2005; Christianen et al, 2018; Kamermans et al, 2018). Although coastal populations have been reported recently in the south of the Netherlands, near shore and offshore in Belgium and in the Dutch part of the Wadden Sea (Bos et al, 2019; Christianen et al, 2018; van der Have et al, 2017; Kerckhof et al, 2018), no living O. edulis of natural origin have recently been recorded in Dutch offshore waters north of the Offshore Wind Farm Egmond aan Zee (OWEZ) where the most northern recent living offshore oyster in the Netherlands was found (Bouma and Lengkeek, 2013, but see Kerckhof et al, 2018).…”