The spread of the invasive ascidian Didemnum vexillum represents a major ecological and economic threat in many parts of the world. Recorded for the first time in Norway in 2020, this species is now established in several localities, often characterized by busy port activities. The new detection and expansion of D. vexillum raise significant concerns in Norway, especially due to the potential extension of its distribution range into higher latitudes. This study presents the results of an in situ monitoring of the growth of eleven D. vexillum colonies in Stavanger between December 2020 and September 2022. Colony growth was calculated from underwater photographs taken approximately once a month. Overall, our findings indicate significant growth of most colonies after 624 days, increasing in size from 78 cm2 to 1008 cm2. Seasonal variations in seawater temperature are a major factor affecting the size and growth of the colonies. Most of the growth occurred during the summer months, when seawater temperature was between 13 °C and 18 °C. A rapid decline in colony growth rates was observed in November, as temperatures dropped below 13 °C, followed by colony regression below ~8 °C. These results therefore confirm the general understanding of D. vexillum as rapidly spreading species, characterized by a high colony growth rate. Its ongoing spread toward northern Norway is likely to have negative impacts on key coastal ecosystems (e.g., kelp forests, rhodolith beds, seagrass meadows), as well as on several industries critical to Norway's economy (e.g., oil industry, aquaculture, fisheries). Based on the information provided here, it is essential to continue implementing measures to prevent further spread to the north and to develop localized mitigation strategies.

中文翻译：

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挪威侵入性海鞘 Didemnum vexillum 的原位生长动力学：来自两年监测研究的见解


入侵性海鞘 Didemnum vexillum 的传播在世界许多地方构成了重大的生态和经济威胁。该物种于 2020 年在挪威首次记录，现在已在几个地方建立，通常以繁忙的港动为特征。D. vexillum 的新发现和扩展在挪威引起了严重关注，特别是由于其分布范围可能扩展到更高的纬度地区。本研究介绍了 2020 年 12 月至 2022 年 9 月期间斯塔万格 11 个 D. vexillum 菌落生长的原位监测结果。根据大约每月拍摄一次的水下照片计算菌落生长。总体而言，我们的研究结果表明，大多数菌落在 624 天后显着生长，大小从 78 cm2 增加到 1008 cm2。海水温度的季节性变化是影响菌落大小和生长的主要因素。大部分生长发生在夏季，海水温度在 13 °C 至 18 °C 之间。 11 月观察到菌落生长速率迅速下降，温度降至 13 °C 以下，随后菌落回归到 ~8 °C 以下。 因此，这些结果证实了对 D. vexillum 作为快速传播物种的普遍理解，其特征是高菌落增长率。它向挪威北部的持续蔓延可能会对关键的沿海生态系统（例如，海带森林、红石床、海草草甸）以及对挪威经济至关重要的几个行业（例如，石油工业、水产养殖、渔业）产生负面影响。根据此处提供的信息，必须继续采取措施防止进一步向北方传播，并制定局部缓解策略。