Ichthyoplankton density and zooplankton biomass in the Benguela upwelling system during MSM18/4 in July and August 2011

Ichthyoplankton density (fish eggs and larvae) and bulk zooplankton biomass in September 2010 were determined for 10 stations in the northern Benguela upwelling system, based on oblique Multinet hauls during the RRS Discovery D356 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 10 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]).

本数据集针对2010年9月本格拉上升流系统北部的10个站位，基于RRS探索号（RRS Discovery）D356航次中斜拖多层采样网（Multinet）的作业数据，测定了鱼卵仔鱼浮游生物（ichthyoplankton）密度与浮游生物总生物量。
所用设备为HYDROBIOS品牌Midi型多层采样网，其口面积为0.25 m²，配备5个孔径500 µm的网具、温氧探头以及内外流量计，用于监测采样网的运动轨迹（用于计算过滤水体体积）与网具堵塞情况。该采样网通过船舷布放，以2节的速度水平拖曳；下放时绞车速度为0.5或0.3 m/s，回收时起升速度为0.2~0.3 m/s。
本次作业在10个站位以斜向拖曳方式采集水柱上层200 m的样品，并根据温氧浓度深度剖面将该上层水柱划分为5个不同深度层。针对每个深度层（对应单个采样网），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与浮游生物总生物量，单位依次为个体/立方米与克湿重/立方米。
此外，通过对各采样网的计算结果求和，完成各站位的面积尺度密度与生物量积分，单位为个体/平方米，计算公式为：Σ（[个体/立方米] × （底层深度[m] - 表层深度[m]））。