Abstract
Historically, various types of shellfish inhabited the Jeju area to the extent that large mounds of shells were found. However, the most endangered of such species, Mactra chinensis, currently inhabits only a few villages on Jeju Island. This pioneering study aimed to explore the effect of the environment on M. chinensis larval growth on Jeju Island. First, we assume that the findings of this study are based on the specific environmental situations and conditions of Jeju Island. This study mostly explored the effects of environment and food diversity (microalgal species) on the growth and survival of M. chinensis (hen clam) larvae. The average seawater temperature ranges between 19 and 22 °C during the summer season. We tested analogous seawater temperature conditions specific to the Jeju coastal environment: 17, 22, 27 and 32 °C. M. chinensis larvae reared at higher temperatures experienced higher growth but lower survival rates, reaching shell lengths of >220 μm at 15 days after hatching. The larvae exhibited the lowest growth (149.3 μm shell length) at 17 °C. Moreover, the M. chinensis larvae had the highest daily growth and survival rate of 10.3 μm and 75.5%, respectively, at a salinity of 30 practical salinity units (psu). For breeding Jeju hen clams, we found that the optimal water temperature and salinity for larval rearing were 22 °C and 30–35 psu, respectively. Larvae fed only I. galbana or Isochrysis sp. also exhibited high growth and survival rates. However, larvae restricted to a diet containing only P. lutheri exhibited low growth and survival rates. Therefore, the optimal diet of M. chinensis larvae should include more than one species of microalga, particularly I. galbana and Isochrysis sp., to increase their growth and survival rates, and hence the productivity of this clam species.
Highlights
Hen clam (Mactra chinensis) is a clam species widely found in the soft sandy bottom of the upper subtidal and intertidal zones of the coastal areas of Russia, Korea, Taiwan and Japan [1]
The growth rate of the larvae increased as the water temperature increased from 17 to 32 ◦C (Table 1)
At water temperatures >22 ◦C, the larvae had grown by 220 μm on day 15 of rearing, but at 17 ◦C, the average shell length was only 149.3 ± 6.29 μm by day 15
Summary
Hen clam (Mactra chinensis) is a clam species widely found in the soft sandy bottom of the upper subtidal and intertidal zones of the coastal areas of Russia, Korea, Taiwan and Japan [1]. The hen clam is the main source of income for the villagers in Gwakjiri, and more than 300 kg of hen clams is produced annually. This shellfish only inhabits the Gwakjiri village, but the catch has recently been decreasing since the average water temperature in the coastal waters of Jeju Island has risen by 1.5 ◦C over the past 40 years due to climate change [3].
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