Effects of temporal dynamics and vertical structure of the seagrass Zostera caulescens on distribution and recruitment of the epifaunal encrusting bryozoa Microporella trigonellata |
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| Authors: | Naoko Kouchi Masahiro Nakaoka & Hiroshi Mukai |
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| Institution: | Akkeshi Marine Station, Hokkaido University, Aikap, Akkeshi, Hokkaido, Japan; Graduate School of Science and Technology, Chiba University, Inage, Chiba, Japan |
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| Abstract: | Seagrass is an ephemeral habitat for epifaunal sessile invertebrates attaching on seagrass leaves, and spatial and temporal dynamics of seagrasses strongly affect the distribution of epifauna. Zostera caulescens Miki, a seagrass species endemic to Japan, provides a complex habitat for epifauna with two types of shoots: vegetative, less than 1 m tall, and flowering, 5–7 m tall. We conducted monthly field observations and a manipulative field experiment to investigate the effects of the seagrass vertical structure and its temporal variation on the distribution and recruitment of the encrusting bryozoan Microporella trigonellata. The density of M. trigonellata on the leaves of flowering shoots, located at the seagrass canopy, varied temporally, reaching maximum in summer and minimum in winter. In contrast, M. trigonellata density on the leaves of vegetative shoots near the sea floor was consistently low throughout the study period. Early recruit bryozoans also showed this temporal and vertical variation in density; thus spatial and temporal variation in recruitment determined the distribution of the whole colonies. The field experiment revealed that the recruitment rate of M. trigonellata was significantly higher at the higher position of the water column (3 m above the sea floor) than at the lower position (0.5 m) in June. However, the recruitment rate was higher at the lower position in October when most of the flowering shoots started falling down. The temporal change in bryozoan habitat selection is considered to be adaptive to maintain their population on the seagrass leaves that show complex temporal dynamics. |
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| Keywords: | Microporella trigonellata recruitment seagrass epifauna temporal variation vertical distribution Zostera caulescens |
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