Setting the stones to restore and monitor European flat oyster reefs in the German North Sea

Abstract

Ecological restoration includes specific technical phases over the course of an ecosystem recovery process. In the marine environment and for oyster reef restoration, the installation and implementation of pilot reefs close the gap between feasibility studies with small‐scale experiments and designated upscaling for marine conservation measures. Against this background, this study presents the design, planning and installation of the first pilot oyster reef in offshore sublittoral regions of the North Sea. The work was conducted as part of marine protected area management in the Natura 2000 site Borkum Reef Ground in the German Bight, in the area of historical offshore oyster grounds. It includes logistical considerations, material selection, methodology for reef base construction and deployment of European flat oysters Ostrea edulis as spat‐on‐shell, young and adult single seed oysters, and spat‐on‐reef, as well as the development of an efficient monitoring approach for reef‐associated biodiversity. Native Oyster Restoration Alliance monitoring methodologies, such as underwater visual census and seabed images were selected, tested and successfully adapted for the pilot oyster reef and study site. The evaluation and optimization of offshore sublittoral oyster reef monitoring are presented here, and biodiversity metrics are put into perspective with data from recent and historical studies. Results show a few mobile fauna species (e.g., fish and decapods) as first colonizers after reef construction. One year later, biodiversity increased due to a larger number of invertebrate and fish species. However, the pilot oyster reef community still represents an early recolonization stage, with lower biodiversity than historical records. This study presents a proof of concept for the design, planning and construction of an offshore oyster reef and indicates stages in the recovery process. Strategies to optimize and to complement reef‐monitoring in challenging environments are discussed, emphasizing additional molecular and functional analyses for future assessments.

A machine learning model and biometric transformations to facilitate European oyster monitoring

“…For the construction of allometric and RF models, and weight-toweight transformation factors, a set of size and weight variables, the location where the oysters were measured/collected, and whether these were single or clustered individuals (also including the number of individuals per cluster) were considered. All measurements were taken between April 2020 and September 2021, within the frame of several field excursions and expeditions (see Acknowledgements) of the RESTORE project (Merk, Colsoul & Pogoda, 2020;Pogoda et al, 2020b;Pineda-Metz et al, 2023). The size variables considered were shell height (H, umbo hinge to longest edge), length (L, longest distance across the valve) and width (Wi, maximum distance between external surfaces of the umbo), these were all measured to the closest 0.01 mm using a digital caliper (Figure 1).…”

Come, tell me how you live: Habitat suitability analysis for Ostrea edulis restoration

“…The restoration of oyster reef habitat is currently realized through the deployment of a flat stone layer (reef base), to counteract sediment dynamics in offshore environments, and through the deployment of young oysters thereon (Pineda‐Metz et al, this issue). The elevation from the sea floor does not exceed 1 m and therefore, in areas with water depths of >20 m, does not present any hindrance for shipping in terms of traffic and manoeuvring (La Peyre et al, 2014; Gillies et al, 2015; Sawusdee et al, 2015; Pineda‐Metz et al, this issue). Also, anchoring in emergency situations does not hinder large‐scale restoration.…”

“…turbidity and current velocity), were not considered in the weighting. Predation was explicitly not considered here, as potential predators of O. edulis are highly mobile species, such as Asterias rubens , Cancer pagurus , and Homarus gammarus (Whilde, 1985; Mascaró & Seed, 2001; Ellrich & Pogoda, in prep), and reef restoration is assumed to attract these predators during the initial stages of reef implementation, independent of the selected sites (Krone et al, 2013; Pogoda et al, 2020b; Pineda‐Metz et al, this issue). During the development and application of the presented analysis, we defined suitability scores of 1–6, with scores 1–3 (optimal, very good, good) regarded as suitable for oyster restoration.…”

“…In the German exclusive economic zone (EEZ), Borkum Reef Ground ( Borkum Riffgrund , BRG) and Sylt Outer Reef – Eastern German Bight ( Sylter Außenriff , SAR) are MPAs for which active conservation measures, including the restoration of biogenic reefs, namely of the native oyster, have been defined (BfN, 2020a). Pilot oyster reefs have been set up in BRG and have been constantly monitored, with the aim of providing the technological and biological background required for the necessary upscaling and further implementation process of such active restoration measures (Pineda‐Metz et al, this issue). As part of the site selection process, a comprehensive list of site‐selection criteria was compiled (Pogoda et al, 2020b): among those are abiotic (e.g.…”