Primary production by phytoplankton along the Kenyan coast during the SE monsoon and November intermonsoon 1992, and the occurrence of Trichodesmium

Phytoplanktonic primary production was measured during the SE monsoon in June–July and during the intermonsoon period in November–December 1992. Primary production was highest on the northernmost transect during the SE monsoon, whereas during the intermonsoon it was highest on the southernmost transect. In general primary production was higher during the intermonsoon, and highest productivity was measured along the southern coast of Kenya. The more stable hydrodynamical conditions during the intermonsoon period promoted the occurrence of the nitrogen-fixing cyanobacterium Trichodesmium, primarily at the shallower stations. Nitrogen fixation assays suggested that this cyanobacterium was responsible for most of the new production. Comparison between net primary productivity, bacterial productivity and benthic respiration suggests that rates of primary production should be higher than measured, implying that primary production can be as high as that in tropical upwelling systems, despite the fact that a regular and well-developed upwelling period does not always seem to occur.