Abundance and biomass of planktonic diatom Proboscia alata and associated species, chlorophyll a, organic carbon and nitrogen concentrations in waters over the Bering Sea middle shelf in August 2001

During most of the vegetation season from late May to early September large-sized diatom alga Proboscia alata forms local patches with high abundances and biomasses in different oceanographic domains of the eastern Bering Sea shelf. For 0-25 m layer average abundance and biomass of species in these patches are 700000 cells/l and 5 g/m**3 (wet weight), while corresponding estimates for the layer of maximal species concentrations are 40000000 cells/l and 38 g/m**3 (wet weight) or 1.6 g C/m**3. These levels of abundance and biomass are typical for the spring diatom bloom in the region. Outbursts of P. alata mass development are important for the carbon cycle in the pelagic zone of the shelf area in the summer season. The paradox of P. alata summertime blooms over the middle shelf lies in their occurrences against the background of the sharp seasonal pycnocline and deficiency in nutrients in the upper mixed layer. Duration of the outbursts in P. alata development is about two weeks and size of patches with high abundances can be as large as 200 km across. Degradation of the P. alata summertime outbursts may occur during 4-5 days. Rapid sinking of cells through the seasonal pycnocline results in intense transport of organic matter to bottom sediments. One of possible factors responsible for rapid degradation of the blooms is affect on the population by ectoparasitic flagellates. At terminal stages of the P. alata blooms percentage of infected cells can reach 70-99%.

在5月末至9月初的大部分植被生长期内，大型硅藻长鼻长棘藻（Proboscia alata）会在白令海东部陆架的不同海洋学区域形成高密度、高生物量的局地斑块。在0-25米水层中，该斑块内该物种的平均丰度与生物量分别为700000个/升与5克/立方米（湿重）；而在物种浓度最高的水层，对应数值可达40000000个/升与38克/立方米（湿重），或1.6克碳/立方米。这类丰度与生物量水平，与该区域春季硅藻水华的典型特征相一致。夏季时节，长鼻长棘藻的大规模暴发对该陆架区远洋带（pelagic zone）的碳循环具有重要意义。中层陆架区长鼻长棘藻夏季水华的悖论之处在于，其发生于显著的季节性密度跃层（pycnocline）背景之下，且上层混合层存在营养盐匮乏的情况。长鼻长棘藻暴发的持续时长约为两周，高密度斑块的跨度可达200千米。夏季暴发的长鼻长棘藻种群可在4至5天内完成降解。藻细胞通过季节性密度跃层快速沉降，会将大量有机质快速输送至海底沉积物中。导致水华快速降解的潜在因素之一，是外寄生鞭毛虫（ectoparasitic flagellates）对其种群的侵染。在长鼻长棘藻水华的末期阶段，被侵染细胞的比例可达到70%-99%。