Female prosome lengths of six calanoid copepod species from Helgoland Roads, North Sea

In temperate seas, multi-voltine copepods show a pronounced seasonal variability in body size, which affects both their reproductive capacity and their accessibility to size -selective predators. Here, we studied seasonal changes of female prosome length from six common copepods, Acartia clausi, Centropages hamatus, Centropages typicus, Paracalanus parvus, Pseudocalanus elongatus, and Temora longicornis between 2000 and 2005 at the time series station Helgoland Roads, southern North Sea. We observed no significant effect of food (measured as phytoplankton carbon content) with size of adult females. Moreover, in none of the species investigated was prosome length significantly correlated with temperature when considering the whole year. Instead, all species had a period of temperature-related size, but for the size distribution during the rest of the year we distinguished two groups of species. Group 1 (Acartia clausi, Centropages hamatus, and Pseudocalanus elongatus ) had a resting phase with females of the same size persisting for > half a year, while in group 2 the time after the temperature-related phase was characterized by irregular size distributions. A female resting phase of Acartia clausi, Centropages hamatus, and Pseudocalanus elongatus has been hitherto unknown. Size distribution control after the temperature-related phase in group 2 is as yet not understood, but the awakening/hatching of resting eggs and/or copepodids may be found to be involved.

在温带海域，多世代桡足类（copepods）的体型表现出显著的季节性变化，这既影响其繁殖能力，也影响其被选择性捕食者捕获的概率。本研究分析了2000-2005年间，北海南部赫尔戈兰航道（Helgoland Roads）时间序列站中六种常见桡足类雌性前体部长度（prosome length）的季节性变化，这六种桡足类分别为Acartia clausi、Centropages hamatus、Centropages typicus、Paracalanus parvus、Pseudocalanus elongatus和Temora longicornis。我们发现，食物（以浮游植物碳含量衡量）对成年雌性体型无显著影响。此外，就全年数据而言，所研究物种的前体部长度均与温度无显著相关性。相反，所有物种均存在一个体型与温度相关的时期，但在一年中的其余时间，我们将这些物种分为两组。第一组（Acartia clausi、Centropages hamatus和Pseudocalanus elongatus）存在一个休眠期，期间雌性个体保持相同体型超过半年；而第二组在温度相关阶段之后，体型分布呈现不规则特征。此前，Acartia clausi、Centropages hamatus和Pseudocalanus elongatus雌性个体的休眠期尚未被发现。第二组在温度相关阶段后的体型分布调控机制尚不清楚，但可能与休眠卵和/或桡足幼体的苏醒/孵化有关。