Washington State Department of Natural Resources, Olympia, WA, United States of America.
Olympia, WA, United States of America.
PLoS One. 2021 Feb 17;16(2):e0229703. doi: 10.1371/journal.pone.0229703. eCollection 2021.
Kelp forests form an important biogenic habitat that responds to natural and human drivers. Global concerns exist about threats to kelp forests, yet long-term information is limited and research suggests that trends are geographically distinct. We examined distribution of the bull kelp Nereocystis luetkeana over 145 years in South Puget Sound (SPS), a semi-protected inner basin in a fjord estuary complex in the northeast Pacific Ocean. We synthesized 48 historical and modern Nereocystis surveys and examined presence/absence within 1-km segments along 452 km of shoreline. Compared to the earliest baseline in 1878, Nereocystis extent in 2017 decreased 63%, with individual sub-basins showing up to 96% loss. Losses have persisted for decades, across a range of climate conditions. In recent decades, Nereocystis predominantly occurred along shorelines with intense currents and mixing, where temperature and nutrient concentrations did not reach thresholds for impacts to Nereocystis performance, and high current speeds likely excluded grazers. Losses predominated in areas with elevated temperature, lower nutrient concentrations, and relatively low current velocities. The pattern of long-term losses in SPS contrasts with stability in floating kelp abundance during the last century in an area of the Salish Sea with greater wave exposure and proximity to oceanic conditions. These findings support the hypothesis that kelp beds along wave-sheltered shorelines exhibit greater sensitivity to environmental stressors. Additionally, shorelines with strong currents and deep-water mixing may provide refugia within sheltered systems.
巨藻林形成了一个重要的生物栖息地，对自然和人为驱动因素有响应。全球对巨藻林所受到的威胁表示担忧，但长期信息有限，研究表明这些趋势在地理上是不同的。我们调查了太平洋东北岸峡湾复合港的半保护内湾南普吉特海峡（South Puget Sound，SPS）中，巨藻 Nereocystis luetkeana 在 145 年间的分布情况。我们综合了 48 项历史和现代 Nereocystis 调查，并在 452 公里长的海岸线沿线的 1 公里长的地段上检查了有无 Nereocystis。与 1878 年最早的基线相比，2017 年 Nereocystis 的范围减少了 63%，个别亚流域的损失高达 96%。在几十年的时间里，这种损失一直在持续，经历了各种气候条件。在最近几十年，Nereocystis 主要出现在水流湍急、混合强烈的海岸线，那里的温度和养分浓度没有达到影响 Nereocystis 性能的阈值，而高速水流可能排除了食草动物。损失主要发生在温度较高、养分浓度较低、水流速度相对较低的地区。SPS 中这种长期损失的模式与上世纪在 Salish 海一个波浪暴露程度更高、更接近海洋条件的地区中，漂浮巨藻数量的稳定性形成了对比。这些发现支持了这样一种假设，即沿受波浪保护的海岸线的巨藻床对环境胁迫因素更为敏感。此外，水流强劲和深水混合的海岸线可能为受保护系统内提供避难所。
