The development of size structure in a young Fucus serratus population

Abstract

Artificial discs were used to monitor the settlement and development of Fucus serratus propagules in five areas cleared of an adult canopy, in order to test the assumptions that sizes of recently settled propagules are normally distributed but that over time plant sizes become more variable and hierarchical. Settlement was spatially (3–20 m) variable only at the beginning and end of the settlement period, and at the time when most settlement took place (88% in a fortnight) no differences between areas were found. Increases in the skewness coefficient, Gini coefficient and coefficient of variation confirmed that there was not a size hierarchy in the recently settled population, but 8 months later sizes of plants were variable and a positive skew in plant sizes (many small and few big) developed. Mortality was high at first (70% in 1 month) but fell considerably later. F. serratus behaves like most higher plants with respect to changing population structure. The observed change in population structure provided evidence of how a “seed bank” develops in an algal population, as 1 year after settlement an estimated 37 000 plants m^-1 are still <1 mm in length.

Key words :

• algal propagules
• density
• Fucus serratus
• seed bank
• settlement
• size structure