Spatio‐temporal variability of zooplankton biomass and environmental control in the Northern Benguela Upwelling System: field investigations and model simulation

Abstract

Spatial and temporal distribution patterns of zooplankton are highly variable in the Northern Benguela Upwelling System. We studied the distribution of zooplankton (size class ≥ 0.33 mm) and used field data from four cruises that took place between March 2008 and February 2011, as well as simulation results of a regional ecosystem model. Remotely sensed sea surface temperatures (SST) and surface chlorophyll concentrations were analysed to investigate environmental influences on zooplankton biomass. The Intense Benguela Upwelling Index showed a distinct seasonal signal throughout the years and the highest upwelling peaks in August/September. Even though surface chlorophyll concentrations were very variable throughout the year, the highest concentrations were always detected in September, following the upwelling of nutrient‐rich water. In field catches, zooplankton biomass concentration in the upper 200 m was highest above the outer shelf and shelf‐break in December 2010 and February 2011, i.e. 6 months after the upwelling peaks. In contrast, zooplankton biomass simulated by the model in the surface water was highest in September. In March/April, biomass maxima were typically measured in the field at intermediate water depths, but the vertical distribution was also affected by extensive oxygen minimum zones. The ecosystem model reproduced this vertical pattern. Although general trends were similar, simulation data of zooplankton standing stocks overestimated the field data by a factor of 3. In upwelling systems, food webs are generally considered to be short and dominated by large cells. However, our field data indicate more small‐sized zooplankton organisms above the shelf than offshore.

Active Carbon Flux of Mesozooplankton in South China Sea and Western Philippine Sea

“…Previous study in western Pacific showed that Chl a concentration could be a crucial factor influencing the abundance and biomass of zooplankton (Sun and Wang, 2017;Yang et al, 2017). In our study, the Chl a concentration at Station B in the SCS was higher than that at station A in the WPS, and it could possibly provide abundant food resources for zooplankton growth and reproduction (Martin et al, 2015), resulting in higher abundance and biomass of mesozooplankton in the SCS. Moreover, the temperature and salinity variation may contribute to the difference in species richness between two stations.…”

Phytoplankton Stimulation in Frontal Regions of Benguela Upwelling Filaments by Internal Factors

“…Irigoien et al (2005) detected nano-and microzooplankton biomass between 200 and 800 mg C m −3 near the shore and less than 100 mg C m −3 in the offshore waters. However, the average zooplankton biomass in the northern Benguela system amounts to 1.3 g C m −2 (Martin et al, 2015). The copepod biomass in maturing water of the southern Benguela upwelling area ranged from 11 to 86 mg C m −3 , which accounted for 5 to 28% of the phytoplankton biomass, and its percentage increased with further aging of the water (Painting et al, 1993).…”

The tropical-subtropical coupling in the Southeast Atlantic from the perspective of the northern Benguela upwelling system

“…Their Lagrangian trajectory analysis is continued here with an analysis of upwelling trajectories. In addition, we use passive tracers [13, 72, 73] which follow the same advection-diffusion equation as potential temperature and salinity (with exception of a specific source term) and do not alter ocean dynamics. Such passive tracers have already been successfully used to track the origin of upwelled water masses in the Californian upwelling system [74].…”