The influence of grazing, sedimentation and phytoplankton cell lysis on the dynamics of a coastal pelagic ecosystem in the Southern Bight of the North Sea was studied during spring/summer 1992. Diatoms in the >8 mu m size fraction dominated during early spring, due to size-differential control by microzooplankton. This diatom spring bloom became silicate depleted and declined by sedimentation. A Phaeocystis bloom developed in early summer. Phytoplankton cell lysis was the major loss factor for Phaeocystis, accounting for 75% of the decline of the bloom. Bacterial production was positively correlated with phytoplankton cell lysis, and bacterial carbon demand could be supplied by cell lysis. This illustrates the importance of phytoplankton cell lysis in providing energy for the microbial loop. A new method (nicotine addition technique) was used to estimate mesozooplankton grazing on microzooplankton. Mesozooplankton appeared to prefer microzooplankton as a food source, though there occasionally was substantial grazing on phytoplankton. We conclude that grazing and sedimentation, as well as cell lysis, are structuring mechanisms for algal bloom dynamics.