Morphological and Anatomical Differences among Three Seagrass Species in a High-energy Coastal Area Typically Dominated by Surfgrass in a Rocky Coastal Area of Shandong Peninsula, China

Surfgrass Phyllospadix iwatensis is the dominant seagrass species in the coastal area of Mashanli, which lies at the east end of Shandong Peninsula, China. To our surprise, some Zostera marina and Zostera caespitosa patches have been recently found adjoining the surfgrass meadows. How the two Zostera species adapt to the high-energy habitats where Phyllospadix spp. thrive, and what kind of differences there are in the morphology and anatomy among the three species are unknown. To understand their adaptation strategies to the environment, we observed their morphological feature and anatomical structure of the three seagrass species by optical microscope. The results showed that much narrower leaves were observed in P. iwatensis, much higher plant density was observed in Z. caespitosa and Z. marina and much lower plant height was observed in Z. marina, which might have contributed to their adaptation in the environment. While for the supporting tissues (the epidermis, mesophyll cells, and vascular bundles for leaves, as well as the epidermis, exodermis and stele for rhizomes), the number of mesophyll cells in the leaves and the proportion of the other tissues in the cross sections in the leaves and rhizomes were significantly different among species. The results suggested that the three species adapt to the high-energy environment through different strategies.