Since the beginning of the 'seventies, upwelling research has become increasingly popular in the path of the Canary and Benguela Current, because of economic consideration, particularly in relation to fisheries and marine geology. Many expeditions were carried out between 1970 and 1977, including 8 cruises of the German R.V. "A. v. Humboldt" operating from Rostock. Measurements covered scales ranging in time from minutes to several years and in space from hundreds of metres to several thousands of kilometres. Zooplankton studies focussed on quantitative, metabolic, taxonomic, and parasitological aspects. Plankton was collected with a WP-2-UNESCO standard net to a maximum depth of 200 m. The epipelagic mesozooplankton consists mainly of copepods, especially calanoids with developmental times of about 20 to 23 days. After an upwetling event, zooplankton is able to double its biomass. This typical biomass increase is independent of coastal distance and depth. The upwetling response lasts about 3 weeks in nearsurface waters, and 6 to 8 weeks in depths below 75 m. A relationship was observed between the duration of seasonal upwelling (that means the numbers of single upwelling events) and the cumulative increase of biomass. This net growth rate of zooplankton biomass is most pronounced at the shelf break, the area with the highest fish biomass, and in the upper 25 m. Differences between the expected and the real rate values in conjunction with the known amount of nutritive demands of fishes allow the estimation of the fish biomass in a given area. The near coastal Ekman upwelling, which is an event in the time scale of about two weeks, also shows seasonality in some areas. Off Northwest Africa the largest expansion was recorded in the first half of the year, extending from 10 ~ N to 24 ~ N, more than 400 km offshore and at least down to 200 ml It contracts in the second half of the year to an area between 20 ~ N and 22 ~ N, 100 to 200 km off the coast and in an average depth of 25 m. These zooplankton biomass patterns are superimposed by mesoscale phenomena, originated by other than Ekman upwelling events. Those are, for example, long coastal parallel waves, producing cells of intensified upwelling and downwelling, and eddies, caused by instabilities in a frontal zone parallel to the coast. Different water masses can be distinguished by indicator species, species combinations or the significant absence of species. This was demonstrated for chaetognaths.

I n short-run experiments herring larvae at the end of the yolk sac stage (SL 6.5 t o 8.5 m) were fed with maize and potato starch to investigate the effect of particle size on food selection. About 20% of the larvae ingested these particles during the experiments.I n the case of maize starch (3 to 26 pm grain size) the size classes from 14 t o 25 pm and in the case of potato starch (5 to 80 pm) the size classes larger than 29 pm were preferred. The highest numbers of ingested grains per larva were 150 maize starch grains and 57 potato starch grains.The selective uptake of these size classes leads to the conclusion that planktonic organisms in this size range-in other words mostly protozoans-may play an important role as a first food source of herring larvae.

Plankton bioniass and indices of metabolism and growth [electron transport system (ETS), glutarnate dehydrogenase (GDH) and aspartatc transcarbarnylase ( A T C ) activities] were studied over a 2,800 km east-west section of the tropical North Atlantic Ocean (21°N) in <200,200-500 and >500 pm size classes. On the large-scale, zooplankton (>200 p) enzymatic activities increased westward in thestudysection, where large cyanobacteria chains (Trichodesmiumspp.) wereobserved. Parallel toit, an increase in rnediurn calanoids (1-2 mrn iength) was observed towards the western part o€ the transect, whereas srnall calanoids (<1 rnrn) were dominant throughout the boundary area of the subtropical gyre.Microplankton ETS and mesoplankton ETS and ATC activitiesseerned to match the wave length of low frequency waves. O u r results suggest that such waves a r e related to the observed enhancement of metabolic activity of rnicro-and mesoplankton. The large-scale and rnesoscale variability observed give evidence of the inadequacy of assurning a steadystate picture of the euphotic zone of tropical and subtropical waters.