Ostrea edulis beds in the central North Sea: delineation, ecology, and restoration

Abstract

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.

The potential of historical ecology to aid understanding of human–ocean interactions throughout the Anthropocene

“…Clockwise from top left: Letters and other forms of correspondence provide insights into contemporary concerns regarding exploitative practices and their impacts upon marine populations (picture: RH Thurstan); popular media can inform when activities such as recreational fishing intensified, locations fished and the catches that occurred (Welsby, 1905); government documents provide data on historical patterns of exploitation (picture: ES Klein); nautical charts provide an indication of the location and extent of certain marine habitats (Olsen, 1883); pictures and newspapers provide insights into species occurrence and size, as well as the frequency with which they were observed or caught ("A RECORD FISH," 7 October 1899, The Queenslander, Brisbane, Queensland, p 714, National Library of Australia); artwork can highlight the use of marine species and their cultural significance (Jean François de Troy, Oyster Lunch, 1735. Public domain, via Wikimedia Commons) habitats, now much reduced or even rendered locally extinct (Kirby, 2004;Thurstan et al, 2014;Alleway & Connell, 2015, Bennema et al, 2020Thurstan et al, 2020;Box 1). Historical evidence also points to significant changes in the occurrence and distribution of non-biogenic marine habitats, forage fish and various species of megafauna resulting from exploitation, habitat destruction, pollution or climate-induced changes (e.g., Ames, 2004;Dulvy et al, 2016;Green et al, 2021;Hall et al, 2012;Kittinger et al, 2013;McClenachan et al, 2006;McClenachan & Cooper, 2008).…”

Offshore Wind Farm Artificial Reefs Affect Ecosystem Structure and Functioning: A Synthesis

“…Furthermore, evidence of adult blue mussel aggregations with distinct macrofaunal communities has been found on soft sediment near turbines (<50 m) in Belgian (Lefaible et al, 2019) and US (HDR, 2020) waters. Continued monitoring is required to determine the spatial extent and longevity of these aggregations to determine their potential designation as reefs and whether these aggregations could contribute to restoring functions of bivalve reefs that historically consisted of Ostrea edulis beds in the North Sea (Bennema et al, 2020).…”

Developing policy and practice for marine net gain

“…The choice of reference framework is not necessarily straightforward. Dramatic transformations of near-shore, estuarine and continental shelf environments in the North Sea as a result of over-exploitation and fishing techniques had already occurred more than a century ago (Thurstan et al, 2013;Bennema et al, 2020), and biogenic reefs were similarly lost from coastal areas of North America and Australia during the 19 th and 20 th centuries (Kirby, 2004;Alleway and Connell, 2015). Restoration on the scale necessary to compensate for these losses seems unlikely, not least because our collective lack of memory of the original extent and condition of marine habitats and species populations means our expectations of ecosystem potential are reduced (Alleway and Connell, 2015); a concept originally termed 'shifting baselines' (Pauly, 1995).…”