Mesopelagic Sound Scattering Layers of the High Arctic: Seasonal Variations in Biomass, Species Assemblage, and Trophic Relationships
Mesopelagic Sound Scattering Layers of the High Arctic: Seasonal Variations in Biomass, Species Assemblage, and Trophic Relationships
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DOI：
10.3389/fmars.2019.00364
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发表时间：
2019-07-12
影响因子：
3.7
通讯作者：
Falk-Petersen, Stig
中科院分区：
文献类型：
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作者：
Geoffroy, Maxime;Daase, Malin;Falk-Petersen, Stig
中层海洋声散射层普遍存在于所有海洋中。作为较高营养水平的猎物和通过生物碳泵在气候调节中，SSL内的远洋生物发挥着重要作用。然而，北冰洋表层沉积物的生物量和物种组成仍然没有得到充分的记录，尤其是在冬季。2016年1月、2016年8月和2017年1月，一台多频超声波探测仪在斯瓦尔巴群岛北部探测到北纬79.8度至81.4度的SSL值。水中拖网采样证实，该水域由北方和北极起源的浮游动物和中上层鱼类组成。北极鳕鱼在8月份的鱼群中占主导地位，1月份的幼鱼喙红鱼占主导地位。大型浮游动物群落主要由8月的蓝藻水母、双足类Themisto libelula和褐褐潮间甲藻等组成，1月份的大型浮游动物群落主要由Thysanoessa inermis组成。SSL位于大西洋水团，8月份在200-700米之间，1月份在50-500米之间。今年1月，SSL在较深的盆地上方较浅和较弱，那里穿透大西洋水较少。夏季以脂类形式存在的能量含量显著高于冬季。夏季水生生物量是冬季的12倍，鱼类多样性略高于冬季(12种对9种)。我们认为，这些差异主要与生活史和个体发育变化有关，导致冬季向中深海层外的海底下降。此外，一些起源于北方的鱼类，如斑点梭鱼，在从大西洋平流到北极时，似乎没有在极地之夜幸存下来。其他种类，主要是幼喙红鱼，在夏季和冬季都很丰富，这意味着该物种可以在极地之夜生存下来，并可能将其活动范围扩大到北极高地。脂肪酸营养标记物表明，北极鳕鱼主要摄食甲壳类桡足类动物，而幼鱼喙红鱼则以磷虾(Thysanoessa spp.)为目标。因此，8月份北极鳕鱼和1月份红鱼的生物量相对较高，表明在SSL内部发生了转变，从夏季以Calanus为基础的食物网转变为冬季以磷虾为基础的食物网。
Mesopelagic sound scattering layers (SSL) are ubiquitous in all oceans. Pelagic organisms within the SSL play important roles as prey for higher trophic levels and in climate regulation through the biological carbon pump. Yet, the biomass and species composition of SSL in the Arctic Ocean remain poorly documented, particularly in winter. A multifrequency echosounder detected a SSL north of Svalbard, from 79.8 to 81.4 degrees N, in January 2016, August 2016, and January 2017. Midwater trawl sampling confirmed that the SSL comprised zooplankton and pelagic fish of boreal and Arctic origins. Arctic cod dominated the fish assemblage in August and juvenile beaked redfish in January. The macrozooplankton community mainly comprised the medusa Cyanea capillata, the amphipod Themisto libellula, and the euphausiids Meganyctiphanes norvegica in August and Thysanoessa inermis in January. The SSL was located in the Atlantic Water mass, between 200-700m in August and between 50-500m in January. In January, the SSL was shallower and weaker above the deeper basin, where less AtlanticWater penetrated. The energy content available in the form of lipids within the SSL was significantly higher in summer than winter. The biomass within the SSL was >12-fold higher in summer, and the diversity of fish was slightly higher than in winter (12 vs. 9 species). We suggest that these differences are mainly related to life history and ontogenetic changes resulting in a descent toward the seafloor, outside the mesopelagic layer, in winter. In addition, some fish species of boreal origin, such as the spotted barracudina, did not seem to survive the polar night when advected from the Atlantic into the Arctic. Others, mainly juvenile beaked redfish, were abundant in both summer and winter, implying that the species can survive the polar night and possibly extend its range into the high Arctic. Fatty-acid trophic markers revealed that Arctic cod mainly fed on calanoid copepods while juvenile beaked redfish targeted krill (Thysanoessa spp.). The relatively high biomass of Arctic cod in August and of redfish in January thus suggests a shift within the SSL, from a Calanus-based food web in summer to a krill-based food web during winter.