Abstract The West Antarctic Peninsula (WAP) region encompasses numerous fjords known to be hotspots of benthic biodiversity and biomass. These ecosystems are undergoing rapid climate warming and oceanographic change; consequent glacial melt and retreat may dramatically alter benthic communities and ecosystem functions in WAP fjords. In addition, there is extreme variability in seasonal productivity and phytodetrital food input to the deep shelf benthos of the WAP. Here we document the flux and utilization of phytodetritus at 530 m depth in Andvord Bay, a WAP glaciomarine fjord, using seafloor time-lapse images spanning a 10-month period, from December 2015 to September 2016. To explore the relationship between sea-surface conditions and detrital export, we developed a color-based method to quantify seafloor phytodetritus cover in time-lapse images, and correlated phytodetritus cover with sea-ice cover and surface wind speed. During the most rapid period of phytodetritus accumulation in early January 2016, approximately 3 cm of phytodetritus was deposited on the fjord floor over six days, representing a large input of organic carbon to the benthos. The timing of this rapid export event was not related to overlying wind conditions and occurred when the fjord was ice-free. To assess the response of the megafaunal community, we measured fecal-pellet production by the dominant surface deposit-feeder, the ampharetid polychaete Amythas membranifera. The deposit-feeding rate of A. membranifera increased substantially during high seafloor phytodetritus cover and returned to background levels for the rest of the autumn and winter. Ampharetids and mobile megafauna were observed to feed throughout the entire time-series, including beneath winter sea ice, suggesting that the delivery of phytodetritus from surface phytoplankton blooms in spring/summer sustains these abundant populations year-round with a sediment food bank. A. membranifera can reach densities of >37 m−2 and, as a population, processes a volume equivalent to the top 1.05 cm of sediment annually. The maximum individual feeding rates measured are comparable to some temperate intertidal deposit feeders. Nonetheless, phytodetritus on 31–73% of the seafloor was consumed by macrofauna or microbial populations not visible in time-lapse photographs, suggesting that recently deposited phytodetritus is processed primarily by these smaller size classes. This study demonstrates the seasonal coupling and subsequent decoupling of detritivore activity in response to a massive detrital deposition event in a deep, subpolar WAP fjord. This work indicates that both megafaunal deposit feeders and smaller size classes play important roles in processing labile organic matter in WAP fjord ecosystems.

中文翻译：

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安德沃德湾（南极洲）冰川峡湾中海底植物碎屑的强烈沉积和快速处理

摘要 西南极半岛 (WAP) 地区包含众多已知是底栖生物多样性和生物量热点的峡湾。这些生态系统正在经历迅速的气候变暖和海洋变化；随之而来的冰川融化和退缩可能会极大地改变 WAP 峡湾的底栖群落和生态系统功能。此外，WAP 深海陆架底栖动物的季节性生产力和植物碎屑食物输入存在极大的可变性。在这里，我们使用 2015 年 12 月至 2016 年 9 月期间 10 个月期间的海底延时图像记录了 WAP 冰川峡湾 Andvord Bay 530 m 深度处植物碎屑的通量和利用。条件和碎屑出口，我们开发了一种基于颜色的方法来量化延时图像中的海底植物碎屑覆盖，以及将植物碎屑覆盖与海冰覆盖和地表风速相关联。在 2016 年 1 月上旬植物碎屑积累最快的时期，大约 3 厘米的植物碎屑在 6 天内沉积在峡湾底部，代表大量有机碳输入底栖动物。这种快速出口事件的发生时间与上覆风况无关，而是在峡湾无冰时发生。为了评估巨型动物群落的反应，我们测量了占主导地位的表面沉积物饲养者（ampharetid polychaete Amythas membranifera）产生的粪便颗粒。A. membranifera 的沉积物摄食率在高海底植物碎屑覆盖期间显着增加，并在秋季和冬季的其余时间恢复到背景水平。观察到两栖类动物和移动巨型动物在整个时间序列中觅食，包括在冬季海冰下，这表明春季/夏季表面浮游植物大量繁殖的植物碎屑通过沉积物食物库全年维持这些丰富的种群。A. membranifera 可以达到 >37 m-2 的密度，并且作为一个种群，每年处理相当于顶部 1.05 cm 沉积物的体积。测得的最大个体喂食率可与一些温带潮间带沉积喂食器相媲美。尽管如此，海底 31-73% 的植物碎屑被大型动物群或延时照片中不可见的微生物群所消耗，这表明最近沉积的植物碎屑主要是由这些较小尺寸的类别处理的。这项研究证明了碎屑动物活动的季节性耦合和随后的解耦，以响应深水、亚极地 WAP 峡湾中的大规模碎屑沉积事件。这项工作表明，大型动物沉积饲养者和较小规模的物种在处理 WAP 峡湾生态系统中的不稳定有机物方面都发挥着重要作用。