Ecological divergence in estuarine transition zone fishes

河口通常被描述为恶劣的环境，在那里，物理特征的陡峭梯度和强烈的潮汐混合只允许少数容忍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)的观察结果，使人们对这种一般范式的有效性产生了怀疑。首先，在一些主要河口的ETZ中，鱼类和浮游动物数量丰富，表明ETZ是一个重要的苗圃地带。在圣劳伦斯河，ETZ支持所有生活史阶段的冶炼和白鳕鱼的高度集中，冶炼的早期生活史阶段在ETZ浑浊的水域中享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。消费者对当地初级生产量表现出很强的选择性，而当地初级生产量只占总碳生产量的一小部分。第三，尽管ETZ是分散的，但我们已经证明了种内栖息地划分和分化的程度令人惊讶。这些观察表明，ETZ促进了比之前猜测的更大程度的生物多样性的存在。我的长期发现资助研究计划的最终目标是评估种内群体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作为不同的种群分化。我们将扩大我们对鱼类种群的研究，并将研究范围扩大到包括其他种类的鱼类，以验证我们主要假设的普遍性。此外，我们还将检验这样一种假设，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分配。该项目的结果将提供与河口生境划分相关的自然选择强度的第一次估计，对于指定关键生境和保护加拿大最重要的河流之一的生物多样性将是无价的。

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.