Flat oyster (Ostrea edulis L.) beds were once a dominant habitat type in the Dutch Delta and North Sea, but overharvesting resulted in soft sediment habitats devoid of oysters. Natural recovery of oyster beds will be slow if the natural substrate is lost and therefore, many oyster restoration projects have been set up worldwide. One way to enhance the success rate of restoring flat oyster beds is adding substrate at the moment that larvae are ready to settle. For this, more insight into the drivers of the timing of larval release is needed, which was the aim of this study. Generalized Additive Models (GAMs) were created based on historical data form the Oosterschelde and Lake Grevelingen of the abundance of swarming flat oyster larvae. It was shown that the temperature explains major part of the variation of larval occurrence. The addition of the temperature sum gave best results in the Oosterschelde. It was shown that the first peak in number of oyster larvae was predicted at a temperature sum of 576 degreedays. In Lake Grevelingen daily temperature yielded higher deviance explained values. Furthermore, the lunar cycle also contributed to the timing of larval release in the Oosterschelde, but not in the Lake Grevelingen, most likely since tides are absent in this waterbody. Chlorophyll-a partly explained larval occurrence in Lake Grevelingen, suggesting food abundance is another driving factor in the timing of gametogenetic processes of flat oysters. Furthermore, day-in-year and mean temperature also contribute significantly to the timing of larval swarming in both water bodies. When validated, this information can be used to predict the optimal time window of deployment of substrate for spat settlement in order to increase the success rate of oyster bed restoration.

中文翻译：

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决定荷兰三角洲地区欧洲扁牡蛎（Ostrea edulis L.）幼虫成群时间的因素：对扁牡蛎恢复的影响

扁牡蛎 (Ostrea edulis L.) 床曾经是荷兰三角洲和北海的主要栖息地类型，但过度捕捞导致没有牡蛎的软沉积物栖息地。如果天然基质丢失，牡蛎床的自然恢复将缓慢，因此，世界范围内建立了许多牡蛎恢复项目。提高恢复平牡蛎床成功率的一种方法是在幼虫准备定居的那一刻添加基质。为此，需要更深入地了解幼虫释放时间的驱动因素，这是本研究的目的。广义加性模型 (GAM) 是根据来自 Oosterschelde 和 Grevelingen 湖的大量成群扁平牡蛎幼虫的历史数据创建的。结果表明，温度解释了幼虫发生变化的主要部分。在 Oosterschelde 中添加温度总和给出了最好的结果。结果表明，牡蛎幼虫数量的第一个峰值预测在576度天的温度总和。在 Grevelingen 湖，每日温度产生了更高的偏差解释值。此外，月球周期也影响了 Oosterschelde 幼虫释放的时间，但在 Grevelingen 湖中没有，很可能是因为该水体中没有潮汐。叶绿素-a 部分解释了 Grevelingen 湖中幼虫的出现，这表明食物丰富是扁平牡蛎配子发生过程时间的另一个驱动因素。此外，日间温度和平均温度也对两个水体中幼虫成群的时间有显着影响。验证后，