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死亡率极高。典型的估计是孵化前的损失超过90%。大多数近地表产卵的浮游生物的卵下沉而不是上升。因此，预计随着数量的急剧减少，胚胎年龄将在水柱中平均向下增加。本研究将量化卵丰度作为发育进程的函数，从而产生卵死亡率的估计，并检查卵发育阶段的垂直分布。采样将使用MEGAPUMP进行，MEGAPUMP是一个2米3分钟1分钟的外置泵送系统，在旋转传送带和板载CTD系统中安装了9个顺序过滤器。在关闭泵的情况下，通过水柱降低MEGAPUMP将产生温度和盐度剖面。抽取后将得到一个9层的50毫米浮游动物的丰度分层剖面，包括除最小的鱿鱼类桡足类动物外的所有动物的卵。这项研究将在华盛顿州的一个峡湾——达布湾的平静水域进行，部署UNOLS船只R/V BARNES上的MEGAPUMP。二零零三年及二零零四年将分别有四次邮轮航行。第一年的两次巡航将与华盛顿大学的一个由布鲁斯·弗罗斯特博士领导的小组合作。他们正在研究硅藻饮食对鸡蛋造成的死亡率。俄勒冈州立大学提出的工作将补充威斯康星大学的项目，因为他们不建议对鸡蛋进行水柱取样。从2月到4月，UW在Dabob湾的采样计划每周进行一次，目的是在3月份海湾出现可靠的硅藻华之前、期间和之后进行采样。这两个程序在船上是兼容的。俄勒冈州立大学建议在2004年进行两次春季巡航，2003年和2004年分别进行两次夏季巡航。在夏季，雌性桡足类仍会大量繁殖，但水柱中不会有大量的硅藻。俄勒冈州立大学和威斯康星大学项目的目标物种将是太平洋Calanus pacificus和太平洋Metridia pacifica，这是达博布湾主要的自由产卵桡足类动物。通常，这两个物种的丰度和繁殖力都很高，足以从几立方米的样本中产生大量的卵，用MEGAPUMP很容易做到。这些桡足类动物的卵很大，很容易辨认。卵子发育将根据形态和DNA含量进行分类，DNA含量是细胞数量的函数。这些，至少其他一些桡足类动物，在孵化时大约有2000个细胞。因此，DNA应该增加10倍，并提供一个精细划分的发育阶段系列。死亡率将根据每个阶段的卵丰度估算来计算。更广泛的含义：桡足类动物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，通常可能是微生物循环中大型动物一侧的第一批消费者。这条管道的主要转移很可能是通过桡足类动物的卵。例如，桡足类卵和早期nauplii是北大西洋鳕鱼幼虫的主要食物。产卵的雌性桡足动物不仅仅是为后代储备；它们为上面的大部分食物网提供食物。良好量化的卵死亡率将是精确建模桡足动物种群动态至关重要的数据，这方面的估计很少。在Dabob湾的研究将是在更复杂的沿海和海洋栖息地进行研究的前奏。这项工作将有助于实现当今浮游生物学的总体目标，美国和国际GLOBEC项目就是例证。通过该项目培训学生将有助于浮游生物学的未来。

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.