The phenology of epiphytic diatoms and epifauna observed on Zostera marina of Arikawa Bay, Nagasaki Prefecture, Japan

We present a descriptive account of the dynamics of epiphytic diatoms, epifauna, and the leaf surface area of Zostera marina in a shallow water ecosystem. We hypothesized that the growth stage of the host macrophyte (i.e., leaf surface area) influenced the presence of epiflora and epifauna, as well as that the leaf surface area and epifaunal population density affected the cell density and species composition of epiphytic diatoms. To evaluate this hypothesis, we quantified the leaf surface area of a host macrophyte (Zostera marina), the presence of epifauna, and the community of epiphytic diatoms that could be observed on the leaves of Z. marina during the period from May 2017 to December 2018. We conducted a descriptive analysis of the time-series observations of leaf surface area, epiphytic diatom density, and epifauna population density. Epiphytic diatom density was low and epifauna density was high during the growing season of Z. marina. Epiphytic diatom density was high and epifauna density was low during the maturation and senescence periods of Z. marina. Our analysis shows that epifauna densities lagged epiflora densities by at least four months, and that epiflora densities lagged leaf area by four months. Therefore, we hypothesized that herbivorous gastropods and amphipods could alter species composition via their preference of food items (active choice) or by ingesting more of the species that were structurally more available (passive preference).