Effects of temperature on fertilization, hatching, larval growth, ingestion, metabolism, and metamorphosis of the purple sea urchins, Heliocidaris crassispina

It is crucial to understand the role of temperature in rearing sea urchin larvae for large-scale production of sea urchin seeds. The development of purple sea urchins, Heliocidaris crassispina, such as fertilization, hatching, embryonic development, larval growth, ingestion, metabolism, and metamorphosis, was investigated at four temperatures: 20, 24, 28, and 32 °C. In the four temperatures, fertilization and hatching of sea urchins first increased with temperature and then decreased. The optimal condition was found at a temperature of 28 °C, where the fertilization and hatching rates exceeded 90%, and embryonic development was highly synchronized. This condition did not differ from the results observed at a temperature of 24 °C (P > 0.05). The fertilization and hatching rates were lower at 20 °C and 32 °C, among which 32 °C had the fastest embryo development but the second highest mortality. In contrast, 20 °C had the slowest embryo development and the most increased mortality. The optimal growth temperature for larvae is 28 °C, at which their growth and development rate are the fastest. However, at 24 °C, it is the second highest. At 20 °C, the growth rate is the lowest, with sluggish physiological responses and the lowest digestion and metabolism capacity. The metamorphosis rate did not differ between 28 and 32 °C (P < 0.05), with 50.0% and 61.1%, respectively, while remaining below 4% at 20 °C. This indicates that temperature significantly impacts the early development of Heliocidaris crassispina sea urchins, whose larvae may be sensitive to low temperatures but have higher temperature tolerance.