Development, Mortality and Sinking of Copepod Eggs, a Field Investigation

据报道，自由产卵的桡足类动物的卵具有极高的死亡率。孵化前的典型损失估计超过90%。大多数浮游卵在近水面产卵的浮游生物下沉，而不是上升。因此，预计随着数量的急剧减少，平均而言，水柱中的胚胎年龄将向下增加。这项研究将量化鸡蛋丰度作为发育进程的函数，从而产生鸡蛋死亡率的估计，并检查鸡蛋发育阶段的垂直分布。采样将使用MEGAPUMP进行，这是一个外置的2 m 3 min-1泵送系统，它有9个安装在传送带中的顺序过滤器和一个机载CTD系统。在关闭泵的情况下，通过水柱降低MEGAPUMP将产生温度和盐度分布。抽水取回将产生一个9级、分层的50毫米浮游动物丰度剖面，包括除最小的金枪鱼桡足类以外的所有浮游动物的卵。这项研究将在华盛顿州峡湾海湾平静的水域中进行，从联合国日内瓦办事处的R/V Barnes号船只上部署MEGAPUMP。在2003年和2004年的两年中，每年将进行四次巡航。第一年的两次巡航将与大学的一个团体合作。由布鲁斯·弗罗斯特博士领导。他们正在研究硅藻饮食对鸡蛋造成的死亡率。拟议的OSU工作将补充UW项目，因为他们不建议对鸡蛋进行水柱采样。达博湾的UW采样计划于2月至4月每周进行，目的是在3月份这个峡湾发生可靠的硅藻水华之前、期间和之后进行采样。这两个程序在国外是兼容的。2004年拟举办两次俄亥俄州立大学春季航行，2003年和2004年各拟举办两次夏季航行。在夏季，雌性桡足类仍将大量繁殖，但水柱中不会有丰富的硅藻。OSU和UW计划的目标物种都将是达博湾主要的自由产卵的桡足类动物--太平洋水蚤和太平洋甲虫。这两个物种通常的丰度和繁殖力都很高，足以从几个立方米的样本中产生大量的卵，这很容易用MEGAPUMP完成。这些桡足类动物有巨大的、特别可识别的卵。卵子的发育将根据形态和DNA含量进行分类，DNA含量是细胞数量的函数。在孵化时，这些以及至少其他一些桡足类动物的细胞数量约为2000个。因此，DNA应该通过10倍增加，并提供一个精细划分的发育阶段序列。死亡率将根据对每个阶段卵子丰度的估计来计算。更广泛的含义：桡足类是海洋和沿海水域的主要浮游动物。它们是从初级生产到适合捕捞的鱼类的主要管道，通常作为微生物环路中大型动物一侧的第一消费者。很可能，这条管道中的大部分转移是通过桡足类动物的卵进行的。例如，桡足虫卵和早期无节幼体是北大西洋鳕鱼幼体的主要食物。产卵的雌性桡足类动物不仅仅是为后代提供食物，它们还在喂食它们上方的大部分食物网。准确量化的卵死亡率将是准确模拟桡足类动物种群动态的关键数据，而目前对这一比率的估计很少。在达博湾进行的一项研究将是在更复杂的沿海和海洋栖息地进行研究的前奏。这项工作将为当今浮游学的总体目标做出贡献，正如美国和国际GLOBEC计划所证明的那样。该项目对学生的培训将有助于浮游学的未来。

Eggs of free-spawning copepods are reported to have extremely high mortality rates. Typical estimates of losses before hatching exceed 90%. Most planktonic eggs of near-surface spawning plankton sink, rather than rise. Thus, it is expected that embryo age will, on average, increase downward in the water column as numbers sharply decrease. This study will quantify egg abundance as a function of developmental progress, thus producing estimates of egg mortality rates, and to examine the vertical distribution of egg development stage. Sampling will be carried out with MEGAPUMP, an overside, 2 m 3 min -1 pumping system that has nine sequential filters mounted in a carousel and an onboard CTD system. Lowering MEGAPUMP through the water column with the pump off will produce temperature and salinity profiles. Pumping on retrieval will produce a 9-level, stratified abundance profile of 50 mm zooplankton, including the eggs of all but the smallest calanoid copepods. The study will be conducted in the calm waters of Dabob Bay, a fjord arm in Washington State, deploying MEGAPUMP from the UNOLS vessel R/V BARNES. Four cruises will be conducted in each of two years, 2003 and 2004. Two cruises in the first year will be in cooperation with a group at the Univ. of Washington headed by Dr. Bruce Frost. They are studying the mortality imposed on eggs by a diatom diet. Proposed OSU work will complement the UW project, since they do not propose water column sampling of eggs. UW sampling in Dabob Bay is scheduled weekly for February through April, intending to sample before, during and after the reliable diatom bloom that occurs in this fjord in March. The two programs are compatible aboard. Two OSU spring cruises are proposed for 2004, and two summer cruises are proposed in each of 2003 and 2004. In summer, female copepods will still be abundant and reproducing, but the water column will not have abundant diatoms. Target species for both OSU and UW programs will be Calanus pacificus and Metridia pacifica, the dominant free-spawning copepods in Dabob Bay. Usual abundances and fecundities of both species are high enough to produce large numbers of eggs from samples of only a few cubic meters, readily done with MEGAPUMP. These copepods have large, specifically recognizable eggs. Egg development will be classified morphologically and by DNA content, which is a function of cell number. Cell number in these, and at least some other copepods, is around 2000 at hatching. Thus, DNA should increase through 10 doublings and provide a finely divided development stage series. Mortality rates will be calculated from estimates of egg abundance in each stage. Broader Implications: Copepods are the dominant zooplankters in both oceanic and coastal waters. They are a main pipeline from primary production to fish suitable for harvest, often perhaps as the first consumers at the large-animal side of the microbial loop. It is likely that a major part of the transfer in that pipeline is via copepod eggs. For example, copepod eggs and early nauplii are the main food for larvae of North Atlantic cod. Spawning female copepods are not just stocking future generations; they are feeding much of the food web above them. Well quantified egg mortality rates will be data essential to accurate modeling of copepod population dynamics, rates for which few estimates exist. A study in Dabob Bay will be a prelude to studies in more complex coastal and oceanic habitats. The work will contribute to the overall goals of planktology at the present day, as exemplified in the U.S. and International GLOBEC programs. Training of a student by the project will contribute to the future of planktology.