Population dynamics of the intertidal barnacle Semibalanus balanoides at three European locations: spatial scales of variability

Spatial variability in the population dynamics of the intertidal acorn barn acle Semibalanus balanoides was investigated using a hierarchical sampling programme. Variability in a number of population parameters (size distribut ion, density, % cover, absolute growth and instantaneous mortality) was det ermined separately for new recruits and adults over 3 spatial scales. Three locations, SW Ireland, the Isle of Man and the west coast of Sweden, which cover a large part of the European range of this species, were selected to investigate variability over a large spatial scale (100s of kilometres). T wo smaller scales, shore (1000s of metres) and site (10s of metres) nested within each location were also used. In addition, temporal variation over t wo 6 mo periods was also examined in the Isle of Man and Ireland. Most vari ability for all population parameters occurred over the largest spatial sca le (location). This was a direct result of differences between Sweden and t he other 2 locations, the Isle of Man and Ireland, which showed highly simi lar levels of all population parameters. The population of S, balanoides at the Swedish location was characterised by high growth rates, large size, h igh levels of mortality and a large turnover of bare space. At the spatial scale 'shore', only 1 population parameter, the growth rate of recruits, sh owed variability. At the smallest scale of 'site', all parameters showed si gnificant variability except growth rate of adults. Calculation of variance components showed that differences between replicates (spatial scale: <0.5 m) accounted for little of the overall variability, in general less than t he scales of site and shore. Examination of temporal variability over two 6 mo periods revealed no difference between time periods and no significant interaction between temporal and spatial scales, Thus, there was consistenc y of spatial variability over time. The potential causes of variability in population parameters of S, balanoides at different spatial scales and the implications for future studies are discussed.