Hopp til hovedteksten
Calanoid and harpactocoid copepods
Zooplankton from a Multinet catch, including calanoid and harpactocoid copepods, apparently also an ostracod, as well as an unidentified individual.
Print friendly version

7th Cruise Diary: Surveillance of plankton and environmental variables in the coastal waters of northwest Africa

The continental shelf of northwest Africa is a well-known upwelling area, sustaining large fisheries on pelagic species. The upwelling implies cool nutrient-rich sub-surface waters replacing the warmer nutrient-poor waters in the coastal surface layers. Phytoplankton primary production takes place in the upper waters since light-levels there are sufficient for photosynthesis.

Hence, nutrient additions to upper layers may boost primary production as well as the secondary production of the zooplankton community that grazes on the phytoplankton. Zooplankton is important food for larger invertebrates such as krill, amphipods and jellyfish, as well as planktivorous fish. By transferring energy from the primary producers to higher trophic levels such as fish, the zooplankton plays a key role in the pelagic ecosystem.

Management of commercial fisheries is presently moving towards an ecosystem-approach. This underlines the importance of understanding the dynamics of the main biological components of the system, and how these are interrelated and affected by physical forcing. During our coastal cruise along northwest Africa we supplement traditional monitoring of fish with sampling of zooplankton, phytoplankton and various types of environmental data. The resulting dataset will become a reference for the autumn-situation in the study-area. This will facilitate future analyses of effects of climate fluctuations and human impacts, and improve the knowledge-basis for resource management.

We left Nouadhibou in Mauritania the 16th November, have now reached 26 °N, and are continuing northwards. From the start, we organized ourselves into different shifts to cover the diel cycle, and within each work-field we have established the routines. Following transects perpendicular to the coastline we collect both zoo- and phytoplankton. Zooplankton is collected from different depth-strata using the Kiel Multinet, and each sample is split in two equal parts. One part is preserved for later taxonomical identification, while the other part is filtered on different sieves and dried to obtain size-fractioned biomass. The phytoplankton is collected with a fine-meshed net, and conserved for later taxonomical identification. Water-samples for analyzes of chlorophyll, nutrient and oxygen concentrations are taken from various depths. Real-time vertical profiles of in situ salinity, temperature, density, oxygen concentrations and fluorescence are collected by CTD-mounted instruments that are calibrated with standard methods.

At this time, Bouya Abderrahmane Mbengue (IMROP, Mauritania) and Agouzouk Abdelaaziz (INRH, Morocco) are in charge of sampling plankton and environmental data on their respective shifts. Our tasks on this cruise cover a wide range of biological and chemical methods, and there is something to learn for everyone.
 

Contact

Kathrine Michalsen
454 29 971