Ghent University, Department of Biology, Laboratory of Protistology & Aquatic Ecology, Krijgslaan 281 (S8), 9000 Ghent, Belgium.
Flanders Marine Institute, Wandelaarkaai 7, 8400 Ostend, Belgium.
Sci Total Environ. 2020 May 10;716:136316. doi: 10.1016/j.scitotenv.2019.136316. Epub 2020 Jan 21.
In the last decades, the North Sea has undergone intense environmental changes which have led to regime shifts that affected all trophic levels. Since the 1970s, both increases and decreases in phytoplankton biomass and production have been reported from different parts of the North Sea. Such conflicting observations may be partly caused by methodological differences, but also reflect regional differences related to bathymetry, hydrodynamics, climate, riverine and Atlantic influence. The Belgian part of the North Sea (BPNS) is a hydrodynamically and bathymetrically complex area under strong human influence, which has been characterized by eutrophication (up to the 1980s) and de-eutrophication (1990s onwards), and pronounced long-term changes in turbidity and water temperature. We used a newly recovered and standardized historic dataset, the Belgian Phytoplankton Database (Nohe et al., 2018), to compare the biomass, composition and seasonality of diatom and dinoflagellate assemblages, two key components of the plankton in the BPNS, between the 1970s and 2000s. Diatoms, especially large-sized taxa, showed an increase from late winter to summer, resulting in a more intense and extended growing season in the 2000s. Dinoflagellates increased year-round but especially in summer. Both diatom and dinoflagellate blooms showed a clear shift towards an earlier bloom start. In addition, while in the 1970s distinct seasonal community types were present, a striking seasonal homogenization in community structure had occurred by the 2000s. Finally, we observed a pronounced increase in the abundance of harmful diatom and dinoflagellate genera. The observed changes are most likely due to an increase in sea surface temperature and water transparency, and changes in nutrient loads and ratios. Our study underscores the importance of recovering previously inaccessible historic data as they can offer unprecedented insights into long-term change in marine ecosystems, which are essential for properly evaluating the impact of human activities on these ecosystems.
在过去的几十年里，北海经历了剧烈的环境变化，这些变化导致了所有营养级都受到影响的生态系统状态的转变。自 20 世纪 70 年代以来，北海不同地区都报告了浮游植物生物量和生产力的增加和减少。这种相互矛盾的观察结果可能部分是由于方法上的差异，但也反映了与水深、水动力、气候、河流和大西洋影响有关的区域差异。受人类强烈影响的北海比利时部分（BPNS）是一个水动力和水深复杂的区域，其特点是富营养化（直到 20 世纪 80 年代）和去富营养化（20 世纪 90 年代以来），以及浊度和水温的长期显著变化。我们使用了一个新恢复和标准化的历史数据集，即比利时浮游植物数据库（Nohe 等人，2018 年），来比较 BPNS 浮游生物的两个关键组成部分，即硅藻和甲藻组合的生物量、组成和季节性，在 20 世纪 70 年代至 2000 年代之间。硅藻，特别是大型分类群，从冬末到夏季增加，导致 2000 年代生长季节更加剧烈和延长。甲藻全年增加，但尤其是在夏季。硅藻和甲藻的爆发都明显提前开始。此外，虽然在 20 世纪 70 年代存在明显的季节性群落类型，但到 2000 年代，群落结构已经明显趋于均匀化。最后，我们观察到有害硅藻和甲藻属的丰度显著增加。所观察到的变化很可能是由于海表温度和水透明度的增加，以及营养物负荷和比例的变化所致。我们的研究强调了恢复以前无法获得的历史数据的重要性，因为它们可以为海洋生态系统的长期变化提供前所未有的见解，这对于正确评估人类活动对这些生态系统的影响至关重要。
