Temporal and multiple scale spatial variation in juvenile and adult abundance of the brown alga Ascophyllum nodosum

Observation of spatial and temporal variation in the distribution and abundance of organisms is often the starting point from which questions and hypotheses about ecological processes arise. This study was designed to investigate spatial variability in abundance of macrorecruits and adults of the brown alga Ascophy11um nodosum using hierarchical sampling programs. Five spatial scales ranging from 10-' to 106 m used, where the largest scale was represented by the distance between 2 areas, Tjarno on the Swedish west coast and the Isle of Man in the Irish Sea. Temporal variation was investigated separately over 3 spat~al scales as comparisons among the years from 1992 to 1995. Significant variation in abundance of 1.5 yr old juveniles was found on 2 spatial scales, 0.1 to 1.5 m and 2 to 30 m. A large variation among replicates suggested substantial variation on a smaller scale (10.15 m). There was no significant variation in the abundance of juveniles among years as suggested by earlier studies. The abundance of the adult population varied between areas but not on smaller spatial scales. There was a significant variation in the abundance of the adult population among years. The potential egg production in female individuals was also investigated as a means of relating the abundance of juveniles to fertility estimates. The number of eggs per conceptacle and the number of conceptacles per receptacle did not vary significantly among indiv~duals and the mean number of eggs per receptacle was estimated to be 7 X 10"he potential egg production was estimated to be 2.5 X log eggs a value much higher than previously reported for fucoids. Given the mean value of 40 juveniles m-', the transition probability from egg to juvenile was estimated to be 2 X 10-'