Ecological divergence in estuarine transition zone fishes

河口通常被描绘成一个恶劣的环境，在那里，陡峭的物理特征和强烈的潮汐混合允许只有少数的耐受性，但丰富的常驻物种共存。在淡水首先与海水混合的河口过渡带（ETZ）的观测结果使人们对这种一般范例的有效性产生了怀疑。首先，在一些主要河口的经济贸易区内鱼类和浮游动物丰富，表明经济贸易区内是一个重要的育苗区。在圣劳伦斯河，经济贸易试验区支持高浓度的所有生活史阶段的胡瓜鱼和小鳕鱼，早期生活史阶段的胡瓜鱼在经济贸易试验区的浑浊水域中具有显著的生长和生存优势。其次，ETZ食物网在水生生态系统中似乎是独一无二的。消费者对只占总碳产量很小一部分的当地初级产品表现出很强的选择性。第三，尽管经济特区具有分散的性质，但我们已经证明了种内栖息地划分和分化的惊人程度。这些观察结果表明，东太平洋经济区促进了生物多样性的存在，其程度远高于以前的推测。我的长期探索基金研究项目的最终目标是评估种内种群开发不同资源的潜力，适应不同的栖息地，并最终在圣劳伦斯经济特区高度动态的环境中分化为不同的种群。我们将扩大对胡瓜鱼种群的研究，并将研究范围扩大到其他鱼类，以验证我们主要假设的普遍性。此外，我们将验证这样一个假设，即这些相同的环境梯度有助于构建整个鱼类群落。最后，碳、氮和硫的稳定同位素分析也将用于评估种内栖息地的划分。该项目的结果将首次提供与河口栖息地划分相关的自然选择强度的估计，并将对加拿大最重要的河流之一的关键栖息地的指定和生物多样性的保护具有宝贵的价值。

Estuaries are often depicted as hostile environments where steep gradients in physical characteristics and strong tidal mixing permit the co-existence of only a small number of tolerant, yet abundant, resident species. Observations in the estuarine transition zone (ETZ), where freshwater first mixes with seawater, cast doubt on the validity of this general paradigm. Firstly, fishes and zooplankton are abundant in the ETZ of a number of major estuaries, indicating that the ETZ is an important nursery zone. In the St. Lawrence River, the ETZ supports high concentrations of all life-history stages of smelt and tomcod, with the early-life history stages of smelt enjoying significant growth and survival advantages in the turbid waters of the ETZ. Secondly, the ETZ food web appears to be unique among aquatic ecosystems. Consumers show strong selectivity for local primary production that constitutes only a minor fraction of total carbon production. Thirdly, we have demonstrated a surprising degree of intraspecific habitat partitioning and divergence in spite of the dispersive nature of the ETZ. These observations suggest that the ETZ fosters the existence of a far greater degree of biodiversity than previously surmised. The ultimate objective of my long-term Discovery-funded research program is to assess the potential for intraspecific groups to exploit different resources, to adapt to distinct habitats and ultimately to diverge as distinct populations within the highly dynamic environment of the St. Lawrence ETZ. We will extend our studies of the smelt populations and expand the scope of the study to include other species of fish to verify the generality of our major hypothesis. In addition, we will test the hypothesis that these same environmental gradients serve to structure the entire fish community. Finally, stable isotope analyses of carbon, nitrogen and sulphur will also be used to evaluate intraspecific habitat partitioning. The results of this program will provide the first estimates of the strength of natural selection associated with the partitioning of habitat in estuaries and will be invaluable for the designation of critical habitat and the conservation of biodiversity in one of Canada's most important rivers.