Short-term response of fish assemblages to instream habitat restoration in heavily impacted streams

ABSTRACT Habitat homogenization has been a major impact in stream ecosystems, and it is considered one of the main drivers of biotic homogenization as well, leading to the loss of water quality and fish diversity. In this study, we added artificial woody structures and leaf packs in physically impacted streams to test if the additions can improve habitat complexity and change the taxonomic and functional structure of fish communities. The experiment was done in eight streams impacted by siltation, deforestation, and habitat homogeneization, inserted in an agricultural landscape from the Upper Paraná River Basin, and lasted 112 days. The provision of artificial microhabitats increased instream habitat diversity by creating patches of organic matter deposits, changing flow, and providing substrate for grass colonization of the instream habitat. The experimental manipulation also changed fish species abundance. Nine species contributed to these changes, five decreased and four increased in abundance, indicating species responded differently to the experimental manipulation. However, overall species richness, diversity, and community functional traits remained unaltered. These results indicate that short-term habitat restoration on a local scale may not be enough to promote changes in fish community attributes of streams that are heavily impacted.摘要 生境均质化是河流生态系统面临的主要干扰之一，同时也是驱动生物均质化的核心因素之一，进而导致水质下降与鱼类多样性丧失。本研究在受物理干扰的河流中布设人工木质结构与落叶袋，以验证此类生境添加措施能否提升河道生境复杂度，并改变鱼类群落的分类与功能结构。实验选取上巴拉那河流域农业景观内8条受泥沙淤积、森林砍伐与生境均质化干扰的河流作为研究样地，实验周期共计112天。人工微生境的布设通过形成有机质沉积斑块、调节水流以及为河道生境的草本定植提供底质，提升了河道内生境多样性。实验干预同时改变了鱼类物种丰度：共有9个物种的丰度发生变化，其中5个物种丰度下降，4个物种丰度上升，表明不同物种对实验干预的响应存在差异。然而，整体物种丰富度、群落多样性以及群落功能性状均未发生显著改变。上述结果表明，局域尺度下的短期生境修复，或不足以促使受严重干扰的河流鱼类群落属性发生明显变化。