Larval euphausiids collected using a 1 x 1 m square frame net with 333-μm mesh aboard Palmer LTER annual cruises off the coast of the Western Antarctic Peninsula, 1993-2013

Euphausiids (krill) are abundant along the Western Antarctic Peninsula where they have important impacts on the marine ecosystem and biogeochemical cycling. Euphausiids develop through a series of morphologically distinct larval stages within the first year of their life cycle. The calyptopis stages are followed by the furcilia stages before individuals recruit to the post-larval population. Larvae collected during Janury were most likely spawned during the preceding weeks or months of Antarctic spring/summer. Euphausia superba and Thysanoessa macrura are the most abundant euphausiid species along the Western Antarctic Peninsula. Euphausia crystallorophias, Euphausia frigida, and Euphausia triacantha are present but less abundant in the region. Samples were collected with a 1 x 1 m square frame net with 333-μm mesh towed obliquely to a depth of typically 300 m. Density of total calyptopis and furcilia larvae (all species combined) was determined for a subset of samples collected on the annual Palmer LTER cruises to cover the latitudinal and cross-shelf gradients of the study region. Larval euphausiid abundance varies spatially as spawning output is not homogeneous across the region. Larval euphausiid abundance also varies year-to-year due to changes in population demographics and environmental conditions.

磷虾目动物（Euphausiids，俗称krill，即磷虾）在南极半岛西部沿岸分布极为繁盛，对该区域的海洋生态系统与生物地球化学循环均具有重要影响。磷虾在生命周期的第一年中，会历经一系列形态特征迥异的幼体发育阶段，依次经历盔形幼体阶段（calyptopis）与褶幼体阶段（furcilia），随后个体便补充进入后幼体种群。1月采集的幼体，其产卵事件大概率发生于南极春季/夏季此前的数周或数月内。南极半岛西部沿岸最为繁盛的磷虾物种为南极大磷虾（Euphausia superba）与长额磷虾（Thysanoessa macrura）；冰磷虾（Euphausia crystallorophias）、冷水磷虾（Euphausia frigida）以及三棘磷虾（Euphausia triacantha）在该区域亦有分布，但种群丰度相对较低。本次研究采用规格为1×1米的方形框架网（网孔孔径333微米）进行样本采集，该网以斜拖方式作业，常规作业深度可达300米。本研究针对年度帕尔姆长期生态研究（Palmer LTER）航次采集的部分样本进行了分析，计算得到所有物种的盔形幼体与褶幼体总密度，以覆盖研究区域的纬度梯度与跨陆架环境梯度。由于该区域的产卵量并非均匀分布，磷虾幼体的丰度存在显著空间异质性。同时，受种群结构动态与环境条件的年度变化影响，磷虾幼体丰度也会呈现逐年波动的特征。