Grange Laura J, Smith Craig R, Lindsay Dhugal J, Bentlage Bastian, Youngbluth Marsh J
Department of Oceanography, University of Hawai'i at Mānoa, Honolulu, Hawaii, United States of America.
Japan Agency of Marine-Earth Science and Technology (JAMSTEC), Natsushima-cho, Yokosuka, Kanagawa, Japan.
PLoS One. 2017 Jan 4;12(1):e0168648. doi: 10.1371/journal.pone.0168648. eCollection 2017.
Medusae can be conspicuous and abundant members of seafloor communities in deep-sea benthic boundary layers. The epibenthic trachymedusa, Ptychogastria polaris Allman, 1878 (Hydrozoa: Trachylina: Ptychogastriidae) occurs in the cold, high latitude systems of both the northern and southern hemispheres, with a circumpolar distribution in Arctic and sub-Arctic areas, and disjunct reports of a few individuals from Antarctica. In January-February 2010, during benthic megafaunal photosurveys in three subpolar fjords along the West Antarctic Peninsula (Andvord, Flandres and Barilari Bays), P. polaris was recorded in Antarctic Peninsula waters. The trachymedusa, identified from megacore-collected specimens, was a common component of the epifauna in the sediment floored basins at 436-725 m depths in Andvord and Flandres Bays, reaching densities up to 13 m-2, with mean densities in individual basins ranging from 0.06 to 4.19 m-2. These densities are 2 to 400-fold higher than previously reported for P. polaris in either the Arctic or Antarctic. This trachymedusa had an aggregated distribution, occurring frequently in Andvord Bay, but was often solitary in Flandres Bay, with a distribution not significantly different from random. Epibenthic individuals were similar in size, typically measuring 15-25 mm in bell diameter. A morphologically similar trachymedusa, presumably the same species, was also observed in the water column near the bottom in all three fjords. This benthopelagic form attained abundances of up to 7 m-2 of seafloor; however, most P. polaris (~ 80%), were observed on soft sediments. Our findings indicate that fjords provide a prime habitat for the development of dense populations of P. polaris, potentially resulting from high and varied food inputs to the fjord floors. Because P. polaris resides in the water column and at the seafloor, large P. polaris populations may contribute significantly to pelagic-benthic coupling in the WAP fjord ecosystems.
水母体可能是深海底栖边界层海底群落中显著且数量众多的成员。浅海底栖硬水母，极地褶胃水母（Ptychogastria polaris Allman，1878年）（水螅虫纲：硬水母目：褶胃水母科）分布于北半球和南半球寒冷的高纬度系统中，在北极和亚北极地区呈环极地分布，在南极洲也有少数个体的分散报道。2010年1月至2月，在南极半岛西部沿三个亚极地峡湾（安德沃德湾、佛兰德斯湾和巴里拉里湾）进行大型底栖动物照片调查期间，在南极半岛水域记录到了极地褶胃水母。从大型岩芯采集的标本中鉴定出的这种硬水母，是安德沃德湾和佛兰德斯湾436 - 725米深度的沉积盆地中浅海动物区系的常见组成部分，密度高达13个/平方米，单个盆地的平均密度在0.06至4.19个/平方米之间。这些密度比之前在北极或南极报道的极地褶胃水母密度高2至400倍。这种硬水母呈聚集分布，在安德沃德湾频繁出现，但在佛兰德斯湾通常单独出现，其分布与随机分布无显著差异。浅海底栖个体大小相似，钟形直径通常为15 - 25毫米。在所有三个峡湾底部附近水域也观察到一种形态相似的硬水母，推测为同一物种。这种底栖浮游形态在海底的丰度高达7个/平方米；然而，大多数极地褶胃水母（约80%）是在软沉积物上观察到的。我们的研究结果表明，峡湾为极地褶胃水母密集种群的发展提供了主要栖息地，这可能是由于峡湾底部有丰富多样的食物输入。由于极地褶胃水母生活在水柱和海底，大量的极地褶胃水母种群可能对南极半岛峡湾生态系统中的水层 - 底栖耦合有显著贡献。
