Temporal changes in secondary production of a population of the subtidal sand snail Umbonium costatum in Hakodate Bay, northern Japan: importance of annual change in age structure

Year-to-year changes in age structure, biomass (B), annual secondary production (P) and PB ratio are described of a population of the subtidal snail Umbonium costatum in Hakodate Bay, northern Japan, during a 6-y period (1982–1988). Population structure and values of biomass and production were highly variable from year to year; the ranges of the annual mean biomass, annual production and PB ratio were 3.71–9.22 g dry tissue m−2, 1.01–4.92 g dry tissue m−2 y−1 and 0.13–1.33 y−1 respectively. Change in the age structure was the most important single factor affecting temporal changes in annual production in this population. The annual production of the population was high when young individuals, which have a small body size and high growth rate, dominated the population. While annual PB ratios in 1983 and 1984 fell within the range of values reported for various other gastropods, those in 1985, 1986, 1987 and 1988 were markedly lower, if the relation between the population PB ratio and life span is taken into account. This demonstrates that production estimates from annual biomass and life-span values may lead to incorrect results in a recruitment-limited population.