Phenology of Codium cylindricum (Ulvophyceae, Bryopsidales) on the central Pacific coast of Japan

Abstract

Abstract Codium cylindricum is a large green alga distributed along the temperate Northeast Pacific coasts. Although the species is edible and contains pharmaceutical substances, little is known about its ecology. In this study, we characterized the phenology of C. cylindricum by monthly observations in Tateyama on the central Pacific coast of Japan from March 2018 to February 2019. The average length of attached thalli in three quadrats (2 × 2 m) was 5 cm from April to July. After disappearing in August, recruits appeared in November and the maximum density (1.08 ± 3.5 inds·m−2) was reached in February. On the sea bottom, detached thalli were present from April to October; the biomass monitored in a single quadrat (2 × 20 m) was high from June to August. Based on monthly observations of 50–100 utricles in each of 18–25 thalli, gametangium formation started in June and reached a peak (i.e., gametangia detected in 75% of thalli and 63.4% of utricles) in September, before the disappearance of the detached thalli. These results strongly suggest that C. cylindricum is annual and reproduces mainly while they are drifting. Therefore, growth during detached stage is critically important to increase biomass and dispersal.