Stream macroalgal flora from Parnaíba River Basin, Brazil: reducing Wallacean shortfall

Abstract: The global biodiversity loss is a consensus. The biodiversity conservations shortfalls make conservation of biological diversity even more challenging. For many taxa, the knowledge about their distributions is deficient, and this is called the Wallacean shortfall. This situation is no different within algae biodiversity, especially in Brazil. There is still an enormous inequity of sample effort, as is the case of the Parnaíba River Basin (Northeast region), which had only 10 algal species in published (the lowest number of algal species reported among the main Brazilian basins). The present work had the objective of increasing the knowledge of algal flora in Brazil by conducting a taxonomic study of the stream macroalgal species of the Parnaíba River Basin. The sampling of macroalgae was carried out in 21 segments of streams from the Middle and Lower Parnaíba Basin, in the Piauí and Maranhão states. Macroalgae were manually removed and preserved in 4% formaldehyde. Environmental characteristics of each segment were measured in order to describe the sampling sites. The taxonomic survey of the macroalgal communities resulted in the identification of 38 taxa in total, of which 32 at a specific level; three vegetative groups; two sporophytic stages of red algae and one unidentified species. Among the 38 species recorded, 37 are new records for the Parnaíba River Basin. Following the same pattern, 23 species are new records for the Brazilian Northeast region, and Microcoleus lacustris represented the first report in Brazil. Despite the fact that it remains the Brazilian basin with the lowest number of algal species documented, this study contributed to the increase of almost five times the number of species sampled in the Parnaíba River Basin (from only 10 to 47 species). These data reinforce that the differences presented in algal diversity in the Brazilian regions are more related to the sampling effort than other factors (e.g. environmental characteristics, geographic distribution, biomes, among others). In addition, this survey illustrates not only the group's lack of information in the region but also shows the importance of this type of study as a tool for expanding the knowledge about biodiversity and its conservation.

摘要：全球生物多样性丧失已是学界共识，生物多样性保护缺口使得生物多样性保护工作更具挑战。对多数分类单元（taxa）而言，其分布相关的认知仍存在显著匮乏，这一现象被称为瓦勒氏分布缺失（Wallacean shortfall），藻类生物多样性领域亦无例外，在巴西尤为突出。当前样本投入仍存在极大不均衡，以帕纳伊巴河流域（Parnaíba River Basin，巴西东北部区域）为例，已发表的藻类物种记录仅10种，是巴西主要流域中藻类物种报道最少的流域。本研究旨在通过对帕纳伊巴河流域溪流大型藻类（macroalgae）物种开展分类学研究，以增进学界对巴西藻类区系的认知。研究于皮奥伊州与马拉尼昂州境内的帕纳伊巴河中下游流域的21个溪流河段开展大型藻类采样：研究人员手动采集藻类样本，并以4%甲醛（formaldehyde）进行固定保存；同时测定各河段的环境特征，以完整描述采样点位信息。针对大型藻类群落的分类学调查共鉴定出38个分类单元，其中32个鉴定至物种水平，另有3个营养类群、2个红藻类孢子体阶段（sporophytic stages）以及1个未鉴定物种。在所记录的38个物种中，37种为帕纳伊巴河流域的新记录物种；23种为巴西东北部地区的新记录物种，而湖生微鞘藻（Microcoleus lacustris）更是巴西境内的首次报道。尽管帕纳伊巴河流域仍是巴西已记录藻类物种最少的流域，但本研究将该流域的采样物种数从仅10种提升至47种，增幅接近五倍。本次研究数据进一步佐证，巴西各区域间藻类多样性的差异更多与采样投入强度相关，而非其他因素（如环境特征、地理分布、生物群系（biomes）等）。此外，本调查不仅凸显了该区域藻类类群研究信息的匮乏，更彰显了此类研究作为拓展生物多样性认知及其保护相关知识的工具的重要价值。