Data from: Oxygen limitations on marine animal distributions and the collapse of epibenthic community structure during shoaling hypoxia

Deoxygenation in the global ocean is predicted to induce ecosystem-wide changes. Analysis of multidecadal oxygen time-series projects the northeast Pacific to be a current and future hot spot of oxygen loss. However, the response of marine communities to deoxygenation is unresolved due to the lack of applicable data on component species. We repeated the same benthic transect (n = 10, between 45 and 190 m depths) over 8 years in a seasonally hypoxic fjord using remotely operated vehicles equipped with oxygen sensors to establish the lower oxygen levels at which 26 common epibenthic species can occur in the wild. By timing our surveys to shoaling hypoxia events, we show that fish and crustacean populations persist even in severe hypoxia (<0.5 mL L−1) with no mortality effects but that migration of mobile species occurs. Consequently, the immediate response to hypoxia expansion is the collapse of community structure; normally partitioned distributions of resident species coalesced and localized densities increased. After oxygen renewal and formation of steep oxygen gradients, former ranges re-established. High frequency data from the nearby VENUS subsea observatory show the average oxygen level at our site declined by ~0.05 mL L−1 year−1 over the period of our study. The increased annual duration of the hypoxic (<1.4 mL L−1) and severely hypoxic periods appears to reflect the oxygen dynamics demonstrated in offshore source waters and the adjacent Strait of Georgia. Should the current trajectory of oxygen loss continue, community homogenization and reduced suitable habitat may become the dominant state of epibenthic systems in the northeast Pacific. In situ oxygen occurrences were not congruent with lethal and sublethal hypoxia thresholds calculated across the literature for major taxonomic groups indicating that research biases toward laboratory studies on Atlantic species are not globally applicable. Region-specific hypoxia thresholds are necessary to predict future impacts of deoxygenation on marine biodiversity.全球海洋脱氧作用预计将引发全生态系统层面的改变。对数十年尺度的氧气时间序列进行分析后可知，东北太平洋目前及未来都将成为氧气流失的热点区域。然而，由于缺乏针对各组分物种的有效观测数据，海洋群落对脱氧作用的响应机制尚未明确。我们在一处季节性低氧峡湾中，使用搭载氧气传感器的遥控水下机器人（Remotely Operated Vehicles），在8年间重复开展了同一条底栖样带（样本量n=10，布设水深范围45至190米）的调查，以此确定26种常见底上生物在野外环境下可存续的最低氧气浓度。通过将调查时段与抬升的低氧事件同步开展，我们发现鱼类和甲壳类种群即便在严重低氧（<0.5 mL·L⁻¹）环境中仍可存活，未出现死亡效应，但移动性物种会发生迁移行为。由此可见，低氧扩张的直接响应是群落结构的崩溃：原本分区分布的定居物种的分布范围发生重合，局域种群密度随之升高。待氧气恢复并形成陡峭的氧气梯度后，各物种原有的分布范围得以重新建立。来自附近VENUS海底观测站的高频监测数据显示，在本研究周期内，研究区域的平均氧气浓度以约0.05 mL·L⁻¹·年⁻¹的速率持续下降。低氧（<1.4 mL·L⁻¹）与严重低氧时段的年持续时长有所增加，这一现象似乎反映了外海水体及邻近乔治亚海峡的氧气动态变化特征。若当前的氧气流失趋势持续，群落均质化与适宜栖息地缩减或将成为东北太平洋底上生物系统的主导状态。原位观测得到的氧气浓度与现有文献中针对主要分类群计算得出的致死及亚致死低氧阈值并不相符，这表明偏向大西洋物种的实验室研究结论并不具备全球普适性。要精准预测脱氧作用对海洋生物多样性的未来影响，必须建立区域特异性的低氧阈值标准。