Fish assemblages in a small temperate estuary on the Argentinian coast: spatial variation, environmental influence and relevance as nursery area

AbstractThe effects of different environmental variables on the fish community structure were evaluated in a small temperate estuary. The biological and environmental data were collected bimonthly between 2007 and 2009 along the main estuarine axis. Multivariate analyses were applied (CLUSTER, SIMPER, CCA) to determine the spatial structure of fish community and to estimate the environmental influence on it. A total of 48 species of "teleost" fishes were observed, with the families Characidae and Sciaenidae presenting the largest number of species, 90% of the catches being juveniles. The fish community was overwhelmingly dominated by one species (Micropogonias furnieri, 88.9%), and only four species contributed more than 1% of total catch (Odontesthes argentinensis5.4%, Brevoortia aurea 1.1%, Paralonchurus brasiliensis 1.1%, and Mugil platanus 1.0%). Estuarine and freshwater stragglers dominated in number of species, followed by freshwater migrants and marine migrants. Three areas with different fish assemblages, with distinctive species and functional guilds, were defined along the main axis. The occurrence and spatial spread of these areas were linked to spatial variation in salinity, which was consistently influenced by discharge from the Río de la Plata and local precipitation. The results highlight the importance of shallow environments as nursery areas and permit emphasis on their susceptibility to environmental changes.

摘要
本研究针对一处小型温带河口，探究不同环境变量对鱼类群落结构的影响。研究于2007至2009年间，沿河口主河道每两个月采集一次生物与环境数据。采用聚类分析（CLUSTER）、相似性百分比分析（SIMPER）及典范对应分析（CCA）等多元统计方法，解析鱼类群落的空间结构并评估环境因子的调控作用。本次调查共记录到48种硬骨鱼（teleost），其中脂鲤科（Characidae）与石首鱼科（Sciaenidae）的物种数量最多；捕获个体中90%为幼鱼。鱼类群落以阿根廷石首鱼（Micropogonias furnieri）占绝对优势，占总捕获量的88.9%；仅4个物种的捕获占比超过1%，分别为阿根廷银汉鱼（Odontesthes argentinensis，5.4%）、金油鲱（Brevoortia aurea，1.1%）、巴西副颈石首鱼（Paralonchurus brasiliensis，1.1%）以及阔额鲻（Mugil platanus，1.0%）。物种组成上以河口性和淡水偶见种居多，其次为淡水洄游种与海洋洄游种。沿河口主河道可划分出3个鱼类组合显著不同的区域，其物种组成与功能群均存在特异性差异。这些区域的分布与空间范围与盐度的空间异质性密切相关，而盐度变化始终受拉普拉塔河（Río de la Plata）径流与当地降水的共同影响。本研究结果凸显了浅水环境作为鱼类育幼场的重要性，并强调了这类生境对环境变化的脆弱性。