Long term marine biodiversity monitoring in coastal Antarctica: Are fewer rare species recruiting?

The physical environment of nearshore Southern Ocean (coastal Antarctica) is altering rapidly in response to climate change, but also has other long cyclicity due to El Nino Southern Oscillation and Southern Annular Mode. Detecting biological responses to such physical change, which is complex in time and space, is very challenging not least because of remoteness, difficulty of access, frequency of iceberg destruction and short funding cycles but also the paucity of research stations with SCUBA (or ROV) facilities. At one of those few, Rothera, Adelaide Island on the West Antarctic Peninsula, we immersed arrays of artificial substrata (settlement panels) for 1 year repeatedly for over two decades. Whilst many ‘mature assemblages’ monitored at nearshore sites around the world, there are few of similar duration for recruitment and colonisation. We report the variability in annual biodiversity descriptive statistics with the crucial context of also recording adjacent long (here defined as >1 decade) term seabed disturbance and biophysical oceanography at Rothera. We ask how variable is annual colonisation, recruitment and early community development in Antarctica's shallows, what aspect of recruitment changes over two decades and in what way? Of 40 recorded, most species recruiting to our panels at 12 m depth at Adelaide Island (67.568° S, 68.127° W) were rare, comprising cheilostome and cyclostome bryozoans, polychaetes, calcarea and demosponge sponges, hydroid cnidarians and ascidians. The most striking finding was a sustained decrease in total richness of recruits over time, mainly due to loss of rare species. Unlike losses of seasonal sea ice, iceberg disturbance and benthos mortality, such findings are unlikely to be climate-forced responses. This raises important questions of whether this is a chance finding, (the data only spans 20 years), driven by a recent complex of stressors and most of all is losing rare species a wider polar problem?

受气候变化影响，近南大洋（南极沿海）的物理环境正快速改变，同时还存在由厄尔尼诺-南方涛动（El Nino Southern Oscillation）与南方环状模（Southern Annular Mode）驱动的长周期波动。探测此类时空格局复杂的物理变化所对应的生物响应极具挑战，这不仅缘于区域偏远、实地作业困难、冰山破坏频发与资助周期短促，更因配备水肺潜水（SCUBA）或遥控水下机器人（ROV）设施的科考站极为匮乏。在西南极半岛阿德莱德岛的罗瑟拉站——此类稀缺站点之一，研究团队在二十余年间反复投放人工基质（附着板），每次部署时长为1年。尽管全球近岸区域已有诸多成熟群落的监测研究，但针对物种招募与定殖过程、且时长与之相当的调查却寥寥无几。本研究结合罗瑟拉站长期（本文定义为时长超10年）的海底扰动与生物物理海洋学观测背景，报告了年度生物多样性描述统计量的变化特征。我们旨在厘清三个核心问题：南极浅海区域的年度定殖、招募与早期群落发育过程存在多大程度的变异？二十余年间，物种招募的哪些特征发生了变化，又是以何种方式变化的？在阿德莱德岛（南纬67.568°，西经68.127°）12米水深处的附着板上，共记录到40种招募物种，其中绝大多数为稀有种，涵盖唇口目与环口目苔藓虫、多毛类、钙质海绵与寻常海绵、水螅刺胞动物以及被囊动物。最显著的研究结果为：随时间推移，招募物种的总丰富度持续下降，这主要源于稀有种的消失。与季节性海冰减少、冰山扰动以及底栖生物死亡等现象不同，该结果不太可能是气候驱动的响应。这引发了一系列关键问题：该现象是否为偶然发现（本研究数据仅覆盖20年）？是否由近期一系列复合胁迫因子所驱动？而最为核心的是，稀有种消失是否为一个广泛存在的极地生态问题？