Seasonal and Long-term Fluctuations in a Population of Patelloida heroldi (Mollusca: Gastropoda) on a Boulder Shore in Japan

Abstract

Population density and size composition of the limpet Patelloida heroldi were investigated over a 6-year period on a boulder shore at Amakusa, western Kyushu. The vertical distribution range extended from the low to the mid intertidal zone. The density on the shore showed an increasing trend over the 6-year period, with a clear seasonal fluctuation: high in spring-summer and low in fall-winter. The size frequency histogram of each sampling occasion had 1-3 peaks. The maximum shell length was 17.80 mm. By following the temporal changes of the size frequency histograms, the recruitment and growth of cohorts were estimated. Recruitment of new cohorts (3-5 mm in shell length) occurred mainly in winter. They grew up to 10 mm within 8 months. Longevity of cohorts was variable, but always less than one and half years. Previous ecological studies on this genus are reviewed in relation to recent taxonomic work.