Seaweed communities are important coastal ecosystems representing good indicators of environmental variation related to climate change and other long-term changes. Long-term variation in the distribution of seaweed communities and individual seaweed species has been intensively investigated; however, long-term studies considering the whole seaweed flora of a geographical area have been infrequently produced, despite of their potential to unravel major changes. The macroalgal flora of a coastal area subjected to urban influences (Conero Riviera, Mediterranean Sea) was investigated comparing the contemporary flora with historical data available for three periods (1941–1946; 1964–1976; 1997–1999). The most evident change was the disappearance of 25–30 species that were present in 1941–1946 (and, in some cases, still in 1964–1976). Such losses are not recent and took place mainly in the years 1940–1960. A general environmental deterioration due to the urbanization of the area of Ancona is suggested as main cause of their disappearance; there is no evidence that their loss was related to climate change. Another major change was the introduction of 9 non-indigenous species, which were probably introduced from the Lagoon of Venice by maritime traffic. One of them, Melanothamnus japonicus, is now very abundant on the Conero Riviera. The results show that present floristic patterns may result from changes that took place at the time scale of many decades, which are rarely considered in studies on benthic vegetation. We suggest that future floristic studies of benthic macroalgae should be based on large-scale programs of DNA barcoding, in order to avoid overlooking invasive cryptic species.

海藻群落是重要的沿海生态系统，是与气候变化和其他长期变化有关的环境变化的良好指标。深入研究了海藻群落和单个海藻物种分布的长期变化；然而，很少考虑到地理区域的整个海藻区系的长期研究，尽管它们有可能揭示重大变化。研究了受城市影响的沿海地区（地中海沿海地区，Conero Riviera）的大型藻类植物区系，并将其与三个时期（1941-1946； 1964-1976； 1997-1999）的历史数据进行了比较。最明显的变化是1941年至1946年（甚至在1964年至1976年）存在的25至30个物种的消失。这种损失不是最近发生的，主要发生在1940年至1960年之间。人们认为，由于安科纳地区的城市化而导致的总体环境恶化是其消失的主要原因；没有证据表明他们的损失与气候变化有关。另一个重大变化是引入了9种非本地物种，这些物种很可能是通过海上交通从威尼斯泻湖引入的。其中之一，日本黑嘴the（Melananothamnus japonicus）现在在Conero Riviera上非常丰富。结果表明，当前的植物区系可能是由于几十年来时间尺度的变化所致，而在底栖植物研究中很少考虑到这种变化。我们建议，对底栖大型藻类的未来植物学研究应基于大规模的DNA条形码程序，以避免忽视侵入性隐性物种。