Weak Concordance between Fish and Macroinvertebrates in Mediterranean Streams

Although anthropogenic degradation of riverine systems stimulated a multi-taxon bioassessment of their ecological integrity in EU countries, specific responses of different taxonomic groups to human pressure are poorly investigated in Mediterranean rivers. Here, we assess if richness and composition of macroinvertebrate and fish assemblages show concordant variation along a gradient of anthropogenic pressure in 31 reaches across 13 wadeable streams in central Italy. Fish and invertebrate taxonomic richness was not correlated across sites. However, Mantel test showed that the two groups were significantly, albeit weakly, correlated even after statistically controlling for the effect of environmental variables and site proximity. Variance partitioning with partial Canonical Correspondence Analysis showed that the assemblages of the two groups were influenced by different set of environmental drivers: invertebrates were influenced by water organic content, channel and substratum features, while fish were related to stream temperature (mirroring elevation) and local land-use. Variance partitioning revealed the importance of biotic interactions between the two groups as a possible mechanisms determining concordance. Although significant, the congruence between the groups was weak, indicating that they should not be used as surrogate of each other for environmental assessments in these Mediterranean catchments. Indeed, both richness and patterns in nestedness (i.e. where depauperate locations host only a subset of taxa found in richer locations) appeared influenced by different environmental drivers suggesting that the observed concordance did not result from a co-loss of taxa along similar environmental gradients. As fish and macroinvertebrates appeared sensitive to different environmental factors, we argue that monitoring programmes should consider a multi-assemblage assessment, as also required by the Water Framework Directive.尽管河流生态系统的人为退化推动了欧盟各国开展多类群生态完整性生物评估（multi-taxon bioassessment），但地中海河流中不同分类群对人类活动压力的特异性响应仍鲜有研究。本研究针对意大利中部13条可涉水溪流的31个河段，探究大型无脊椎动物（macroinvertebrate）与鱼类群落的物种丰富度和组成是否沿人为压力梯度呈现协同变化。各采样点的鱼类与无脊椎动物分类群丰富度并无显著相关性。然而，曼特尔检验（Mantel test）结果显示，即便在统计控制环境变量与样点空间邻近性的影响后，两类群仍存在显著但微弱的相关性。采用偏典范对应分析（partial Canonical Correspondence Analysis）进行方差分解的结果表明，两类群的群落分别受不同的环境驱动因子调控：无脊椎动物群落受水体有机质含量、河道与底质特征影响，而鱼类群落则与溪流水温（与海拔呈镜像关联）及当地土地利用类型相关。方差分解结果还揭示，两类群间的生物交互作用可能是决定群落协同性的潜在机制。尽管两类群间的一致性显著，但强度较弱，这表明在这些地中海流域的环境评估中，二者无法互为替代类群。事实上，物种丰富度与嵌套性格局（即物种贫乏样点仅包含物种丰富样点中类群的一个子集）均受不同环境驱动因子影响，这说明观测到的协同性并非源于两类群沿相似环境梯度的协同物种丧失。鉴于大型无脊椎动物与鱼类对不同环境因子具有敏感性，我们认为监测方案应纳入多类群群落评估，这也是水框架指令（Water Framework Directive）的明确要求。