DataSheet_1_Performance of European oysters (Ostrea edulis L.) in the Dutch North Sea, across five restoration pilots.csv

IntroductionThe European flat oyster (Ostrea edulis) is a biogenic reef former, internationally recognised as threatened and declining in the NE Atlantic by OSPAR and one of the focal species in nature inclusive designs in offshore windfarms in The Netherlands. Oyster reefs offer habitat to many other benthic hard substrate and fish species and provide ecosystem functions such as shelter and feeding grounds. European flat oyster reefs have disappeared from the Dutch North Sea in the early 1900s due to overfishing and diseases but are now subject of nature restoration under the Dutch Marine Strategy.
MethodSince 2018, pilot projects have started in the Dutch North Sea to restore European flat oysters at suitable locations, such as offshore windfarms or natural reefs, which are protected from bottom trawling. We compared European flat oyster performance in five pilot projects, using translocated adult oysters sourced from Ireland, Norway, and the Netherlands. The aim of this research was to assess the performance of translocated oysters between pilots, to assess the installation and monitoring techniques, and to come forward with recommendations for future pilot projects.
ResultsWe found that translocation of both foreign sourced flat oyster populations (Ireland and Norway in nearshore and offshore areas) and local oysters (in nearshore areas) result in good oyster performance. Oysters were able to grow (max 3.67 mm/month) and reproduce (larvae present) in their new environment. We found that growth rate was explained by origin and average water temperature, to a lesser extent by number of months, location and salinity and not to other environmental factors such as pH and O2. Correlations between growth and environmental conditions need to be considered with caution, since not all pilots were sampled just before and after the growing season. Oysters were Bonamia-negative at the start and end of the pilots, indicating that the offshore Dutch North Sea is still Bonamia-free.
Discussion, conclusions, recommendationsBy the year 2050 more than ten new offshore farms will be constructed in the Dutch North Sea and some sites will be suitable for oyster restoration. We conclude that local and foreign sourced oysters performed well at all locations. Based on the success and failure of the different outplacement and monitoring techniques, we provide recommendations on good practice for the future, including developing standardized monitoring protocols. This will enable better inter-site comparisons in upcoming oyster restoration pilots.

引言
欧洲扁牡蛎（Ostrea edulis）是一种造生礁构筑生物，被东北大西洋海洋环境保护委员会（OSPAR）列为东北大西洋海域受威胁且种群呈衰退趋势的物种，同时也是荷兰海上风电场自然包容式开发设计的核心物种之一。牡蛎礁为众多依附硬质底质生存的底栖生物与鱼类提供栖息生境，并提供庇护场所、觅食场等生态系统服务功能。20世纪初，荷兰北海海域的欧洲扁牡蛎礁因过度捕捞和病害侵袭彻底消失，但如今依据《荷兰海洋战略》，该类礁体已被纳入自然修复项目范畴。

研究方法
自2018年起，荷兰北海海域启动多项试点项目，在适宜区域——如受底拖网禁捕保护的海上风电场或自然礁体——开展欧洲扁牡蛎修复工作。本研究选取源自爱尔兰、挪威及荷兰的成年移植牡蛎，对5个试点项目中欧洲扁牡蛎的生存表现开展对比分析。本研究的目标为：对比不同试点间移植牡蛎的生存表现，评估牡蛎投放与监测技术，并为后续试点项目提出针对性建议。

研究结果
研究结果表明，无论是源自海外的扁牡蛎种群（爱尔兰与挪威种群，分别应用于近岸与远海区域），还是本地牡蛎种群（应用于近岸区域），移植后的生存表现均较为优异。移植牡蛎可在新环境中正常生长（最大生长速率达3.67毫米/月）并完成繁殖（可检测到幼体存在）。研究发现，牡蛎生长速率主要受种群来源与平均水温影响，其次受养殖时长、采样点位及盐度的影响，而与pH值、溶解氧等其他环境因子无显著相关性。由于并非所有试点项目均在生长季前后开展采样，因此在分析牡蛎生长与环境条件的相关性时需谨慎解读结果。试点项目全程（起始与结束阶段）的牡蛎样本均呈包拉米虫（Bonamia）检测阴性，表明荷兰北海远海海域目前仍无包拉米虫感染。

讨论、结论与建议
至2050年，荷兰北海海域将新建十余座海上风电场，其中部分区域将适宜开展牡蛎修复工作。本研究得出结论：无论种群来源为本地还是海外，牡蛎在所有试点点位均表现优异。结合不同牡蛎投放与监测技术的实施成效，本研究为后续工作提出了标准化操作规范建议，其中包括制定统一的监测规程。该规范可助力未来牡蛎修复试点项目开展跨点位的更精准对比分析。