This study sheds light on the influence of dissolved oxygen (DO) and temperature on fine-scale zooplankton vertical distribution in a seasonally stratified, enclosed marine lake on the Croatian island of Mljet. Unusually high precipitation during the spring and summer of 2014 caused extended hypoxia above the bottom in the autumn. Nauplii, copepodites, Oithona nana and appendicularians strictly avoided the layers of reduced DO. Copepods Oithona similis, Mesaiokeras hurei, oncaeids, and polychaeta trochophore comprised a community adapted to the hypoxic bottom layer (10%-14% dissolved oxygen). Oncaeids were the most abundant and were presented by two small species: Oncaea zernovi and the more numerous Monothula subtilis. Polychaeta larvae were extraordinary numerous, too. Proliferation of ocaeids and polychaeta larvae in hypoxic zone could be related to their ability to feed on detrital matter and associated microbial community. Contrary, low abundance of other copepod developmental stages were found in the whole water column suggesting that the high load of organic material and hypoxic events inhabited their reproduction. Our study has documented the dramatic impact of local environmental changes on the planktonic community, providing additional evidence that low oxygen has an effect on the distribution and abundance of zooplankton.

这项研究揭示了克罗地亚Mljet岛上一个季节性分层，封闭的海洋湖中溶解氧（DO）和温度对小型浮游动物垂直分布的影响。2014年春季和夏季异常高的降水量导致秋季缺氧现象扩展至底部以上。Nauplii，copepodite，Oithona nana和阑尾虫严格避免了溶解氧降低的层。pe足类的Oithona similis，Mesaiokeras hurei， oncaeids和polychaeta trochophore组成了一个适应低氧底层的群落（10％-14％的溶解氧）。Oncaeids数量最多，有两个小物种：Oncaea zernovi和数量更多的Monothula subtilis。Polychaeta幼虫也非常多。低氧区的油性和多壳幼虫的增殖可能与其摄食碎屑物质和相关微生物群落的能力有关。相反，在整个水柱中发现了其他co足类动物发育阶段的低丰度，表明有机物质的高负荷和缺氧事件使它们繁殖。我们的研究记录了局部环境变化对浮游生物的巨大影响，提供了其他证据表明低氧对浮游动物的分布和丰富度有影响。