Published online by Cambridge University Press: 05 December 2011
Data from the Continuous Plankton Recorder survey are used to compare the distribution and seasonal and year-to-year variations in the abundance of the plankton of the area of the Rockall Channel with both the shelf and the adjacent oceanic areas. It is argued that the distribution and size of overwintering stocks of zooplankton provide the key to understanding the dynamics of the plankton of this area.
It would appear that, due to inherent limitations to the net rate of increase of zooplankton populations, the distribution of the overwintering stocks has an influence on the distribution and abundance of most species through the rest of the year. This affects the dynamics of the seasonal cycle and also influences the form of year-to-year changes in abundance
The plankton of the area of the Rockall Channel is characterised by low overwintering stocks, coupled in spring with higher rates of population increase as compared with the adjacent shelf. There is a pronounced spring bloom of phytoplankton, which does not appear to be controlled by grazing, followed by a period of nearly five months of relative stability of stocks of both phytoplankton and zooplankton. It is suggested that during this period the zooplankton graze the daily production of phytoplankton, the growth of which is determined to a large extent by nutrients recycled from the zooplankton. The effects of this pattern of dynamics on the form of year-to-year changes in the abundance of the plankton over the last few decades is discussed.