MEPS 240:39-48 (2002)  -  doi:10.3354/meps240039

ABSTRACT: Rocky shore monitoring around the Sullom Voe Oil Terminal in Shetland has produced a 20 yr dataset of population fluctuations for 40-plus species at 15 to 20 sites separated by distances up to 30 km. Synchrony in population changes was quantified by correlation among series of abundance categorised on quantitative scales. Two periods were analysed separately, pre- and post-1992, following changes in methods and extent of monitoring. Positive average correlations among sites were found for 10 out of 16 species pre-1992 and for 23 out of 26 post-1992, statistically significant for 4 and 8 species for the 2 periods, respectively. The intertidal barnacle Semibalanus balanoides showed most synchrony among sites for both periods, while dogwhelks Nucella lapillus and macroalgae (Fucus vesiculosus, F. serratus, Mastocarpus stellatus) had very low average correlations among sites. Littorina saxatilis was the only other species with significant positive correlation among sites in both periods. Corallinaceae, Verrucaria maura and V. mucosa, and Littorina neglecta were less synchronised pre-1992 than post-1992, while L. obtusata showed less synchrony post-1992. Differences in reproductive biology and ecology failed to explain patterns of synchrony among species. Species with planktonic larvae were no more likely to be synchronised than those without. There was a tendency for species living higher on the shore to be more synchronised post-1992, but species predominant on wave-exposed shores were no more synchronous than sheltered-shore species. The more synchronised species in this study need to be monitored at relatively few sites to detect change, whereas more sites may be needed for species in which change occurs on a local scale. Population synchrony also suggested usefulness of species as indicators of large-scale change: the barnacle S. balanoides is the best indicator among species in the study area.

KEY WORDS: Population synchrony · Rocky shore communities · Monitoring methods