A cost-effective approach to decreasing the disease transmission of the sea urchin Strongylocentrotus intermedius: New information for seed production and longline culture

Developing a cost-effective approach to effectively removing problematic (dead, diseased and asymptomatic) individuals is important to decrease the disease transmission in seed production and longline culture of the sea urchin Strongylocentrotus intermedius. A simple facility, which was divided into areas M (the upper 70 mm part) and W (the lower 70 mm part), was proposed to separate the problematic and healthy sea urchins based on the differences in their behavioral performances. The V-shaped plastic corridor was inside these two unseparated areas and connected by an upper platform.In experiment 1, fresh kelp was placed in the platform of area M, twenty-five healthy small sea urchins (~10 mm of test diameter) and another twenty-five problematic individuals (previously exposed to the bacteria liquid) were put on the area W of the facility. The present study found that the average proportion of sea urchins distributed in areas M and W was 0.47/0.53. Significantly higher morbidity (~9 times) and poorer performances in righting behavior, foraging behavior, Aristotle's lantern reflex and adhesion force were consistently found in area W than those in area M. The number of sea urchins with diseased Aristotle's lantern was significantly higher (~24 times) than that of those without diseased Aristotle's lantern, among sea urchins without the black-month disease performances in area W. This approach, therefore, is effective in separating problematic sea urchins (including asymptomatic infectors).In experiment 2, five problematic sea urchins (previously exposed to the bacteria liquid but without disease symptoms) and thirty-five healthy sea urchins were maintained in both the new facility group (group S) and the control group (group C) for 7 days. This study found significantly higher morbidity (~2 times) and significantly poorer performances in adhesion force, righting behavior and Aristotle's lantern reflex occurred in group C compared to those in group S. These results indicate that the new facility greatly decreases disease transmission and leads to better performance in fitness-related behaviors of cultured sea urchins.The present study provides valuable information on effectively decreasing the disease transmission in seed production and longline culture of sea urchins.