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Influence of environmental factors on the development of bottom ice protist communities during the winter–spring transition

机译：冬春过渡期环境因素对底层冰生物界发育的影响

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ABSTRACT: Seasonal changes in the abundance and taxonomic composition of bottom ice protists (i.e. diatoms, flagellates, and dinoflagellates) were assessed in the first-year landfast ice of Franklin Bay (Canadian Beaufort Sea) from 24 February to 20 June 2004. On each sampling day, bottom sea-ice protists were collected at sites of high (10 cm) and low (10 cm) snow cover. The net observed growth rates of diatoms and nanoflagellates were significantly higher during the pre-bloom (24 February to 25 March) than the bloom (ca. 3 April to 23 May) period under low snow cover but were not different under high snow cover. In contrast, dinoflagellates showed relatively constant net observed growth rate before and during the bloom period under both snow covers. These results indicate that the 3 protist groups responded differently to changes in the light regime during the growth period. The decline of the protist community after the bloom period was related to a combination of factors including nitrogen deficiency and melting processes. Prior to the bloom, flagellated cells, likely heterotrophic, dominated numerically under high snow cover, whereas autotrophic protists, especially solitary diatoms, prevailed under low snow cover. During the bloom period, colonial diatoms such as Nitzschia frigida, N. promare, Navicula sp. 6, N. pelagica, and Fragilariopsis cylindrus dominated the bottom ice community irrespective of snow depth, although abundances were higher under low snow cover. The arborescent colonial N. frigida, a key species of landfast ice across circumarctic regions, was the most abundant bottom ice algal diatom throughout the entire season. During the post-bloom period, colonial and solitary diatoms declined more rapidly than nanoflagellates, suggesting that nanoflagellates, presumably heterotrophic, were better adapted to melting sea-ice conditions. Our results demonstrated that the availability of nitrate in the surface water limits the accumulation of algal biomass in the bottom horizon of Arctic landfast ice during the vernal growth season.
机译：摘要：于2004年2月24日至6月20日在富兰克林湾（加拿大波弗特海）的第一年陆生冰中评估了底层冰原生生物（即硅藻，鞭毛和鞭毛鞭毛）的丰度和生物分类组成的季节性变化。采样日，在高（> 10厘米）和低（<10厘米）积雪的地点收集了海底生物。在低积雪条件下，在开花前（2月24日至3月25日），硅藻和纳米鞭毛虫的净观测增长率明显高于开花（4月3日至5月23日），但在高积雪条件下没有变化。相反，在两种雪盖下，鞭毛藻在开花期之前和期间都显示出相对恒定的净观测增长率。这些结果表明，在生长期间，3个原生生物群体对光照变化的反应不同。开花期后，原生生物群落的减少与氮缺乏和融化过程等多种因素有关。在开花之前，鞭毛状细胞（可能是异养的）在高积雪的情况下在数量上占优势，而自养生物（尤其是孤立的硅藻）在低积雪的情况下占优势。在开花期，殖民地硅藻如 Nitzschia frigida ， N。 Promare ， Navicula sp.。 6， N。不论积雪深度如何，尽管中低层积雪的丰度较高，但远洋白桦林和西洋樱草仍在底冰群落中占主导地位。树木状殖民地N。 frigida 是整个环冰地区的陆地冰的重要种类，是整个季节中最丰富的底冰藻硅藻。在开花后的时期，殖民和孤立的硅藻比纳米鞭毛虫下降得更快，这表明可能是异养的纳米鞭毛虫更适合于融化海冰条件。我们的结果表明，在春季生长季节，地表水中硝酸盐的可用性限制了北极陆生冰底地平线中藻类生物量的积累。

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