Physical control of plankton population abundance and dynamics in intertidal rock pools

Little is known about the population structure and dynamics of plankton of intertidal rock pools. A numerical model was developed for rock pool plankton with growth limited by both tidal washout and the stress associated with adverse conditions in high-shore pools. This model predicts that a stress tolerant species will tend to have maximum population densities in high-short pools and that populations will fluctuate in opposite phase to the spring-neap tidal cycle. Conversely, where a species is susceptible to stress in high-shore pools, the maximum population density is likely to occur lower on the short, and numbers in upper shore pools will cycle in phase with the spring-neap cycle. These two alternative predictions were sufficient to classify the dynamics of the most abundant species in time series taken from rock pools in the isle of Man, The dinoflagellate Oxyrrhis marina followed the predictions of the stress tolerant model. In comparison. the spatiotemporal patterns of other taxa, including a ciliate, a dinoflagellate and cryptophytes, suggested stress-susceptible lifts histories.