Data_Sheet_1_State of the California Current 2019–2020: Back to the Future With Marine Heatwaves?.pdf

The California Current System (CCS) has experienced large fluctuations in environmental conditions in recent years that have dramatically affected the biological community. Here we synthesize remotely sensed, hydrographic, and biological survey data from throughout the CCS in 2019–2020 to evaluate how recent changes in environmental conditions have affected community dynamics at multiple trophic levels. A marine heatwave formed in the north Pacific in 2019 and reached the second greatest area ever recorded by the end of summer 2020. However, high atmospheric pressure in early 2020 drove relatively strong Ekman-driven coastal upwelling in the northern portion of the CCS and warm temperature anomalies remained far offshore. Upwelling and cooler temperatures in the northern CCS created relatively productive conditions in which the biomass of lipid-rich copepod species increased, adult krill size increased, and several seabird species experienced positive reproductive success. Despite these conditions, the composition of the fish community in the northern CCS remained a mixture of both warm- and cool-water-associated species. In the southern CCS, ocean temperatures remained above average for the seventh consecutive year. Abundances of juvenile fish species associated with productive conditions were relatively low, and the ichthyoplankton community was dominated by a mixture of oceanic warm-water and cosmopolitan species. Seabird species associated with warm water also occurred at greater densities than cool-water species in the southern CCS. The population of northern anchovy, which has been resurgent since 2017, continued to provide an important forage base for piscivorous fishes, offshore colonies of seabirds, and marine mammals throughout the CCS. Coastal upwelling in the north, and a longer-term trend in warming in the south, appeared to be controlling the community to a much greater extent than the marine heatwave itself.

加利福尼亚流系(California Current System, CCS)近年来经历了环境条件的剧烈波动，对其生物群落造成了显著影响。本研究整合了2019至2020年整个加利福尼亚流系范围内的遥感、水文及生物调查数据，旨在评估近期环境变化如何影响多个营养级的群落动态。2019年北太平洋形成了一次海洋热浪，至2020年夏末时，其覆盖面积达到有记录以来的第二高值。然而2020年初的高大气压力驱动了加利福尼亚流系北部区域较强的埃克曼沿岸上升流，而暖温异常则持续停留在远海区域。加利福尼亚流系北部的上升流与较低水温营造了相对高生产力的环境：富含脂质的桡足类生物量上升、成年磷虾体型增大，且多种海鸟的繁殖成功率呈正向表现。尽管存在上述环境条件，加利福尼亚流系北部的鱼类群落组成仍为暖水关联物种与冷水关联物种的混合体。在加利福尼亚流系南部海域，海水温度已连续第七年高于平均水平。与高生产力环境关联的幼鱼物种丰度相对偏低，而鱼卵仔鱼浮游生物群落以远洋暖水物种与广布种的混合类群为主。加利福尼亚流系南部海域中，暖水关联海鸟物种的种群密度也高于冷水关联海鸟。自2017年以来种群复苏的北方鳀鱼，仍为整个加利福尼亚流系内的食鱼鱼类、远洋海鸟群落以及海洋哺乳动物提供了重要的饵料基础。相较于本次海洋热浪本身，加利福尼亚流系北部的沿岸上升流与南部海域长期增温的趋势，对群落结构的调控作用更为显著。