Ichthyoplankton density and zooplankton biomass in the Benguela upwelling system during MSM17/3 in January and February 2011

Ichthyoplankton density (fish eggs and larvae) and bulk zooplankton biomass in January/February 2011 were determined for 38 stations in the northern Benguela upwelling system, based on oblique Multinet hauls during the FS Maria S. Merian MSM17/3 cruise. A HYDROBIOS Multinet, type Midi (0.25 m**2 mouth area) was equipped with five nets of 500 µm-mesh size, temperature and oxygen probes, and an inner and outer flow meter to monitor the net's trajectory (for volume filtered calculations) as well as net clogging. The Multinet was handled over the side, towed horizontally at 2 knots. Winch speed when fearing was 0.5 or 0.3 m/s, heaving velocity 0.2 - 0.3 m/s. The Multinet was towed obliquely at 38 stations sampling the upper 200 m of the water column, which were divided into five different depth strata after inspection of temperature and oxygen concentration depth profiles. Ichthyoplankton densities and zooplankton biomass were calculated for each depth stratum (=single net) from total abundance and the volume of water filtered [individuals per m**3 and g wet weight per m**3, respectively]. In addition, densities and biomass were integrated over the area for each station [individuals per m**2], as sum of calculations for each net: Sum ([individuals per m**3]*Delta (depth bot[m]-depth top [m]).2011年1-2月，研究人员针对本格拉上升流系统（Benguela upwelling system）北部38个站位，通过“玛丽亚·S·梅里安号”（FS Maria S. Merian）MSM17/3航次期间的倾斜式多网拖网作业，测定了鱼卵仔鱼浮游生物（Ichthyoplankton）密度与大型浮游动物总生物量。本研究采用HYDROBIOS公司Midi型多网浮游生物网（口面面积0.25 m²），该网配备5张网目尺寸为500 µm的网具、温氧传感器，以及内置与外置流量计，用于监测拖网运动轨迹以计算过滤水体体积，并监控网具堵塞情况。该多网拖网通过舷侧下放，以2节的航速水平拖曳；下放作业时绞车速度为0.5或0.3 m/s，起升速度为0.2~0.3 m/s。研究人员在38个站位开展倾斜拖网，对水柱上层200 m进行采样，并结合温氧浓度深度剖面的分析结果，将采样水柱划分为5个不同的深度分层。针对每个深度分层（即对应单张网），基于总个体数与过滤水体体积，分别计算得到鱼卵仔鱼浮游生物密度（单位：个/m³）与浮游动物生物量（单位：g 湿重/m³）。此外，针对每个站位，通过对各分层计算结果求和完成区域尺度的密度与生物量整合（单位：个/m²），计算公式为：Σ（[个体数/立方米] × （底层水深 - 表层水深））。