Growth and maturation of two populations of Sargassum horneri (Fucales, Phaeophyta) in Hiroshima Bay, the Seto Inland Sea

Abstract

Seasonal growth and maturation patterns of two Sargassum horneri populations were surveyed in Hiroshima Bay on the western Seto Inland Sea. Both S. horneri populations began to exhibit rapid growth in autumn, exceeding a daily increase in plant length of 10 mm/day. However, there are several differences in seasonal timing for maturation and reaching maximum plant size. Plants of the Ohno-seto population, inhabiting the innermost area of Hiroshima Bay, reached their maximum plant size in December and became senescent after January. Plants of the Matsugahana population, inhabiting the mouth of the bay, continued to grow during winter and reached their maximum plant size in April. Senescence occurred after May. The largest difference in the seasonal patterns of the two S. horneri populations is most likely to be in the timing of maturation. In the Ohno-seto population, receptacle formation of the plants begins in November, and the eggs are released from late November to January. The plants settled as embryos spend the winter in an early stage of development. In the Matsugahana population, on the contrary, the plants spend the winter as adults and gradually produce receptacles. Abundant egg release of the Matsugahana population occurred in April and May.