Metapopulation dynamics of Tigriopus brevicornis (Harpacticoida) in intertidal rock pools

Abstract

Rock pools above the level of mean high tide are frequently occupied by harpacticoid copepods of the genus Tigriopus. The network of populations in separate pools can be viewed as a metapopulation. However, in a dynamic environment subject to rainfall, tidal flushing and wave wash, there may be no particular structure to rock pool populations. Time series samples from pools at different levels on the shore were used to test for the presence of separate local population dynamics of T. brevicornis (Müller). Sample counts taken from the same pool 2 d apart showed autocorrelation in pools from the upper and middle of the range occupied by T. brevicornis. However, the dynamics of different pools were not strongly correlated. For counts of copepodites and adults, the degree of coupling between pools was a function of distance. The height of high tide affected counts in pools. Copepodite and adult numbers fell in pools at the lower end of the species range during spring tides. In comparison, there were spring-tide-associated increases in copepodite and adult numbers in pools above the mean height of high tide. Persistence of populations on the shore may therefore be aided by upshore movement of copepodites and adults during spring tides. Multivariate analysis of stage structure in pools suggested that pools acted as individual systems over a period of 31 d. The results indicate a degree of local population dynamics in separate pools, but the inferred metapopulation structure does not follow the classical model, since extinction events were rare in pools above the mean high tide level.