The thecosome pteropods Limacina helicina and L. retroversa are important contributors to the zooplankton community in high-latitude environments but little is known about their distribution and life cycle under polar conditions. We collected the early life stages (< 1 mm) of the thecosome population in 2012 and 2013 at a bi-weekly to monthly resolution in fjord highly influenced by Arctic waters as well as Atlantic inflows (Adventfjorden, Svalbard, 78°N), together with environmental parameters. L. retroversa only occurred episodically, in association with the inflow of Atlantic water, with low numbers and random size distributions. This suggests that this boreal species does not fulfill its life cycle in Adventfjorden. In contrast, young specimens of L. helicina were present during the entire study. Veligers hatched in late summer/autumn and measured 0.14 mm on average. They grew with rates of 0.0006 mm day⁻¹ over the 10–11 months of development. Only thereafter, growth accelerated by one order of magnitude and maximal rates were reached in autumn (0.0077 mm day⁻¹). Our results indicate that L. helicina reaches a size of 1 mm after approximately 1.5 years in Adventfjorden. We therefore suggest that L. helicina overwinters the first year as a small juvenile and that it needs at least 2 years to reach an adult size of 5 mm in Adventfjorden. This reveals an complex and delicate aspect of the life-cycle of L. helicina and further research is needed to determine if it makes the population especially vulnerable towards climate changes.

Thecosome pteropods Limacina helicina和L . 逆流是高纬度环境中浮游动物群落的重要贡献者，但对其在极地条件下的分布和生命周期知之甚少。我们在 2012 年和 2013 年以每两周到每月一次的分辨率收集了 2012 年和 2013 年在受北极水域和大西洋流入（Adventfjorden，斯瓦尔巴群岛，78°N）影响很大的峡湾中的早期生命阶段（<1 毫米），一起与环境参数。升。逆反仅偶尔发生，与大西洋水的流入有关，数量少且大小分布随机。这表明这种北方物种并没有在 Adventfjorden 完成其生命周期。相比之下，L 的年轻标本。在整个研究过程中都存在螺旋藻。Veligers 在夏末/秋季孵化，平均长 0.14 毫米。在 10-11 个月的发育过程中，它们以 0.0006 mm day ^{-1 的}速度增长。仅此后，生长速度加快了一个数量级，并在秋季达到最大速率（0.0077 mm 天^-1）。我们的结果表明L . 螺旋藻在 Adventfjorden 大约 1.5 年后达到 1 毫米的大小。因此，我们建议L。helicina在第一年作为一个小幼鱼越冬，它需要至少 2 年才能在 Adventfjorden 达到 5 毫米的成年大小。这揭示了L生命周期的一个复杂而微妙的方面。helicina和进一步的研究需要确定它是否使人口特别容易受到气候变化的影响。