Development, Settlement, and Post-settlement Growth

Summary The sea cucumber Apostichopus japonicus is an economically important species along the northwest Pacific Coast, including China, Democratic People’s Republic of Korea, Republic of Korea, Russia, and Japan. In the present chapter, we summarize knowledge on the embryonic and larval development of A. japonicus , as well as the impacts of various environmental factors on these processes. A. japonicus is a dioecious broadcast spawner. Its life cycle can be divided into eight major stages: fertilization, blastula, gastrula, auricularia, doliolaria, pentactula, juvenile, and adult. The fertilized, mainly demersal eggs measure ∼165 μm in diameter, and develop into freely rotating blastulae in 14 h at 20–21 °C. The embryos then develop into auricularia larvae over the following 34 h, at which time they gain the ability to feed. When the auriculariae grow to their maximum size of ∼800–950 μm, they shrink and transform into doliolariae, and subsequently into pentactulae after completion of metamorphosis. The development of buccal and ambulacral podia indicates the onset of the juvenile stage. It takes almost two years for A. japonicus to reach sexual maturity, and the life span of this species is commonly estimated to be at least five years. The influence of environmental factors, such as temperature, salinity, and planktic food, on larval development and growth, as well as substrate selection during metamorphosis are discussed. Transitional functions of locomotory and feeding organs in larvae, behavioral characteristics during settlement, and interindividual variations in early growth rates are also examined.