Plankton is a collective name for organisms that float freely in the water column and are strongly dependent on the current for their propulsion. Plankton can be divided into two groups: phyto- and zooplankton. Phytoplankton includes organisms that perform photosynthesis, such as diatoms, dinoflagellates and cyanobacteria (blue algae). Zooplankton, on the other hand, consists of heterotrophic organisms that need organic components as food. These include copepods and heterotrophic protozoa, but also larger marine animals such as jellyfish and fish larvae.  

Plankton is of great importance in marine ecosystems, also in the BNS. Firstly, they form the basis of the marine food pyramid. In addition, the plankton acts as a key piece between habitats on the seabed and in the higher water column for the exchange of energy, biomass and nutrients. In addition, phytoplankton is responsible for half of the global oxygen production, which also absorbs enormous amounts of CO2. However, plankton can also have a negative impact on the surrounding habitats. For example, a high supply of nutrients can cause phytoplankton population growth that is too rapid, resulting in algae blooms. If the phytoplankton dies, the water can temporarily become deoxygenated, which is detrimental to bottom-dwellers and can mean food shortages for both fish and birds. 

The plankton in the Belgian part of the North Sea (BNS) is typically coastal. Occasionally, the plankton community is also influenced by species that come along via the influx of Atlantic water (Van Ginderdeuren 2013). As phytoplankton is the most important food source of zooplankton, a change in the dynamics of phytoplankton can strongly influence the presence of zooplankton. The presence of phytoplankton is mainly determined by temperature and the availability of light and nutrients.

Research on plankton teaches us more about the biodiversity of seawater. Within the framework of the LifeWatch project, the composition of the plankton community and how it is influenced by environmental factors such as temperature, nutrients, pH and pollution are studied in the long term. The different taxonomic groups in a water sample are determined with the ZooSCAN (zooplankton) and the FlowCAM (phytoplankton). On board of the RV Simon Stevin, this diversity is also observed directly in the water with the Video Plankton Recorder (VPR) and the Flow cytometer, for zooplankton and phytoplankton respectively. This data on the composition of the plankton in the BNS is available via the LifeWatch data explorer.