Natural gradients in temperature, nutrient loading, and primary productivity contribute to broad scale regional differences in the food web structure of large lakes, such as Lake Michigan. These factors influence spatial patterns of primary production and resource reliance of high trophic level consumers. Secondary consumers, such as larval fish and predatory zooplankton represent an important intermediate link within large lake food webs, but spatial patterns in their density and physiological condition have not been as thoroughly assessed. To analyze the spatial and temporal condition of secondary consumers in Lake Michigan, we sampled the ubiquitous spiny water flea, Bythotrephes cederströmii during the 2015 Cooperative Science and Monitoring field year in Lake Michigan. Monthly estimates of density, instar frequency, length-at-age, and RNA content of Bythotrephes were compared between the eastern and western shores of southern Lake Michigan. Condition indices differed seasonally between the eastern and western shores. During June-August, Bythotrephes were more abundant and in better condition along the eastern shore of Lake Michigan, but in September, all indices were comparable between transects. While this study focused on a single year, other studies across multiple years have demonstrated consistent upwellings and cooler temperatures along the western shore of southern Lake Michigan relative to the eastern shore. A temporal lag in preferable environmental conditions along the western shore may be common and lead to delayed growth and reduced physiological condition of secondary consumers, such as predatory zooplankton and late spring emerging larval fish.

温度、养分负荷和初级生产力的自然梯度导致大型湖泊（如密歇根湖）食物网结构的广泛区域差异。这些因素影响初级生产的空间格局和高营养级消费者的资源依赖。次级消费者，如幼鱼和捕食性浮游动物是大型湖泊食物网中的重要中间环节，但其密度和生理条件的空间模式尚未得到彻底评估。为了分析密歇根湖二级消费者的时空状况，我们对无处不在的刺水蚤Bythotrephes cederströmii进行了采样在密歇根湖的 2015 年合作科学和监测领域年期间。在密歇根湖南部的东岸和西岸之间比较了Bythotrephes的密度、龄龄、年龄长度和 RNA 含量的月度估计值。东海岸和西海岸的状况指数季节性不同。在 6 月至 8 月期间，Bythotrephes沿密歇根湖东岸更丰富，条件更好，但在 9 月，样带之间的所有指数都具有可比性。虽然这项研究只关注一年，但多年的其他研究表明，相对于东岸，密歇根湖南部西岸沿线的上升流和气温较低。西海岸沿线较佳环境条件的时间滞后可能很常见，并导致次级消费者的生长延迟和生理状况降低，例如捕食性浮游动物和晚春出现的幼鱼。