Temporal variability of viruses, bacteria, phytoplankton and zooplankton in the western English Channel off Plymouth

The temporal distribution of autotrophic and heterotrophic components of th e planktonic community was studied from samples collected weekly at station L4, located to the south of Plymouth, UK, from October 1992 to January 199 4. Phytoplankton succession followed the typical pattern of temperate water s. the development of a summer Gyrodinium aureolum bloom being the most pro minent feature. Bacterial numbers were significantly correlated with temper ature during autumn and winter, whereas resource availability and predation , including viruses, appear to be the most important controlling factors in spring and summer. High mesozooplankton densities, mainly copepods, were o bserved throughout most of the study associated with a series of diatom blo oms, and also during autumn when low phytoplankton biomass was measured. Th is data set was analysed in order to build up conceptual trophodynamic mode ls whereby the role of biological communities on the cycling of organic mat ter could be inferred. The results obtained in this study provide empirical evidence supporting the existence of a succession of trophic organization patterns in a coastal temperate environment. Classical models (herbivorous or microbial webs) appeared episodically whereas transition models (multivo rous web) dominated throughout most of the seasonal cycle.