Animals on marine flowers: does the presence of flowering shoots affect mobile epifaunal assemblage in an eelgrass meadow?
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Eelgrass, Zostera marina, produces two types of shoots: morphologically simple vegetative shoots and highly branched flowering (reproductive) shoots, the latter found only in summer months. We examined whether the abundance and diversity of mobile epifaunal assemblage are affected by the presence of flowering shoots in an eelgrass meadow of Otsuchi Bay, northeastern Japan. Comparisons of epifauna in natural vegetation revealed that density and species richness did not differ significantly between sites consisting of both flowering and vegetative shoots, and those only of vegetative shoots. A transplant experiment, conducted to examine the colonization rates of epifauna to defaunated eelgrass planted with different combination of vegetative and flowering shoots, showed no obvious variation in abundance and species richness. At species level, the density of some species such as a tanaid Zeuxo sp. and a polychaete Platynereis sp. was higher at sites and/or treatments with flowering shoots, whereas that of some gastropods, such as Lirularia iridescens and Siphonacmea oblongata was higher at sites without flowering shoots. The species-specific response led to dissimilarity of epifaunal assemblage between sites and among treatments with different densities of vegetative and flowering shoots. Similar patterns observed for natural vegetation and the transplant experiment suggest that the variation in assemblage structure is caused by habitat selection of each species, for example, the utilization of flowering shoots as feeding ground and nursery by Zeuxo sp.
KeywordsMacrophyte Assemblage Structure Transplant Experiment Shoot Density Vegetative Shoot
We wish to thank the staff of the Otsuchi Marine Research Center, Ocean Research Institute, University of Tokyo, for facilitation of our research. We are specially indebted to B. Nyden, K. Morita, K. Hirano, K. Sado, M. Kurosawa and Y. Iwama for their help in the fieldwork. We are grateful to Y. Hashiguchi and Y. Okuzaki for laboratory assistance, and to M. Shimanaga for taxonomic identification of copepods. The research is partially supported by grants from the Ministry of Science, Education and Culture, Japan to M. N. (nos. 08740954 and 08680594), and by the research fellowship program by Japan Society for the Promotion of Science to S. L. W. (no. S-97122).
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